Scopus
EXPORT DATE: 9 June 2011

Sun, Z.a  b  c , Zhou, H.a  d , Yang, Q.d , Sun, Z.e , Bao, S.f , Yao, H.g 
Hydrothermal Fe-Si-Mn oxide deposits from the Central and South Valu Fa Ridge, Lau Basin
(2011) Applied Geochemistry, 26 (7), pp. 1192-1204. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79956275698&partnerID=40&md5=917b23fba99ab2015e5065f5e8ae01c4
AFFILIATIONS: Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 
Graduate University of Chinese Academy of Sciences, 100049 Beijing, China; 
Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao 266071, China; 
National Key Lab of Marine Geology, Tongji University, Shanghai 200092, China; 
School of Petroleum Engineering, China University of Petroleum, Qingdao 266555, China; 
Wuhan University of Technology, Wuhan 430070, China; 
Guangzhou Marine Geological Survey, Guangzhou 510075, China
ABSTRACT: A series of samples from the Hine Hina hydrothermal field (HHF) and the Mariner hydrothermal field (MHF) in the Central and Southern Valu Fa Ridge (VFR), Lau Basin were examined to explain the source origin and formation of the hydrothermal Fe-Si-Mn oxide deposits. The mineralogy was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, and energy-dispersive spectroscopy (EDS). For the Fe-Mn oxide crusts in the HHF, varying amounts of volcanic fragments and some seawater contributions were recognized, along with higher concentrations of Mn, Al, Co, Ni, Zn, Sr, Mo, elevated ∑REE and negative Ce anomalies. In contrast, the Si-rich oxide samples of the MHF were enriched in Cu, Pb and Ba, indicative of proximity to a hydrothermal jet. Moreover, conductive cooling of hydrothermal fluid evoked the Si-rich deposit formation in the MHF. The Sr, Nd and Pb isotope data provided further constraints regarding the source and formation of the Fe-Si-Mn deposits in the VFR by showing that the samples of the HHF are a mixture of three components, namely, hydrothermal fluid, seawater and volcanic materials, whereas the samples of the MHF were dominated by hydrothermal fluids. The seawater had a minor influence on the Nd isotope data, and the Pb isotope data exhibited a close association with the substrate rock and preformed volcaniclastic layers in this area. The occurrence of relatively high Mn/Fe ratios in the hydrothermal deposits of this area may be a good indicator of the propagating activities of the VFR over geological time. © 2011 Elsevier Ltd.
DOCUMENT TYPE: Article
SOURCE: Scopus

Padoan, M.a , Garzanti, E.a , Harlavan, Y.b , Villa, I.M.a  c 
Tracing Nile sediment sources by Sr and Nd isotope signatures (Uganda, Ethiopia, Sudan)
(2011) Geochimica et Cosmochimica Acta, 75 (12), pp. 3627-3644 begin_of_the_skype_highlighting              3627-3644      end_of_the_skype_highlighting. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955978245&partnerID=40&md5=7f2c3b76f1c94867952e37bc3d9cf351
AFFILIATIONS: Laboratory for Provenance Studies, Geological Sciences and Geotechnology Department, Milano-Bicocca University, Piazza della Scienza 4, 20216 Milano, Italy; 
Geological Survey of Israel, 30 Malkhei Israel St., 95501 Jerusalem, Israel; 
Institut für Geologie, Universität Bern, Erlachstrasse 9a, 3012 Bern, Switzerland
ABSTRACT: Strontium and neodymium isotopes, measured on diverse mud and sand fractions of sediment in transit along all major Nile branches, identify detritus sourced from Precambrian basements, Mesozoic strata, and Tertiary volcanic rocks exposed along the shoulders of the East African rift and in Ethiopian highlands. Sr and Nd isotopic ratios reflect the weighted average of detrital components generated in different catchments, allowing us to discriminate provenance, calculate sediment budgets, and investigate grain-size and hydraulic-sorting effects.87Sr/86Sr and 143Nd/144Nd range, respectively, from as high as 0.722 and as low as 0.5108 for sediment derived from Archean gneisses in northern Uganda, to 0.705 and 0.5127 for sediment derived from Neoproterozoic Ethiopian and Eritrean basements. 87Sr/86Sr and 143Nd/144Nd, ranging 0.705-0.709 and 0.5124-0.5130 for Blue Nile tributaries, are 0.704-0.705 and 0.5127-0.5128 for largely volcaniclastic sediments of River Tekeze-Atbara, and 0.705-0.706 and 0.5126-0.5127 for main Nile sediments upstream Lake Nasser.Model mantle derivation ages (tDM), oldest in Uganda where sediment is principally derived from the Congo Craton (3.4-3.0Ga for Victoria and Albert Nile), progressively decrease northward across the Saharan Metacraton, from 2.6Ga (Bahr el Jebel in South Sudan), to 2.4-2.2Ga (Bahr ez Zeraf across the Sudd), and finally 1.6-1.3Ga (White Nile upstream Khartoum). Instead, tDM ages of Sobat mud increase from 0.9 to 1.5Ga across the Machar marshes. TDM ages are younger for sediments shed by Ethiopian (1.2-0.7Ga) and Eritrean basements (1.5-1.2Ga), and youngest for sediments shed from Ethiopian flood basalts (0.3-0.2Ga).Integrated geochemical, mineralogical, and settling-equivalence analyses suggest influence on the Nd isotopic signal by volcanic lithic grains and titanite rather than by LREE-rich monazite or allanite. Because contributions by ultradense minerals is subordinate, intrasample variability of Sr and Nd ratios is minor. In Blue Nile, Atbara and main Nile sediments of mixed provenance, however, the Nd ratio tends to be higher and tDM ages lower in largely volcaniclastic mud than in mixed volcaniclastic/metamorphiclastic sand.The complete geochemical database presented here, coupled with high-resolution bulk-petrography and heavy-mineral data, provides a key to reconstructing erosion patterns and detrital fluxes across the whole Nile basin, and to investigate and understand how sources of sediment have changed in the historical and pre-historical past in relation to shifting climatic zones across arid northern Africa. © 2011 .
DOCUMENT TYPE: Article
SOURCE: Scopus

Stallard, R.F.
Weathering, landscape, and carbon in four paired research watersheds in eastern Puerto Rico
(2011) Applied Geochemistry, 26 (SUPPL.), pp. S370-S372. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955947154&partnerID=40&md5=e5047669187bff80865b2db58a2ba15c
AFFILIATIONS: US Geological Survey, 3215 Marine St. (Ste E127), Boulder, CO 80303, United States
ABSTRACT: The U.S. Geological Survey Water, Energy, and Biogeochemical Budgets Program in eastern Puerto Rico involves a double pair-wise comparison of humid-tropical montane streams on granitic bedrock and fine-grained volcaniclastic bedrock. For each bedrock type, one catchment is covered with mature rainforest, and the other catchment is affected by grazing, cropping, and minor urbanization. Biogeochemical budgets were monitored for fifteen years and included water, major dissolved constituents, nutrients, carbon, and sediment. To adjust for differences in runoff, the relation between annual runoff and annual yield were used to project the yields for all the rivers to an intermediate common runoff. Observed and adjusted rates of physical denudation greatly exceed rates expected for a dynamic equilibrium, except for the forested river on volcaniclastic bedrock. Deforestation and agriculture can explain the accelerated physical erosion in the two developed catchments. Something else, possibly climate or forest-quality change, must explain the excessive erosion in the forested river on granitic bedrock. Particulate organic carbon yields are closely linked to sediment yields, which are in turn, far in excess of equilibrium yields. This implies that much of the particulate carbon transport in the four rivers is being caused by enhanced erosion perhaps due to human activities or environmental change. Dissolved organic and inorganic carbon show a weak runoff signal, and there is no evidence of human perturbations to dissolved carbon production or silicate weathering in the four watersheds. © 2011.
DOCUMENT TYPE: Article
SOURCE: Scopus

Kirkland, C.L.a , Spaggiari, C.V.a , Pawley, M.J.a , Wingate, M.T.D.a , Smithies, R.H.a , Howard, H.M.a , Tyler, I.M.a , Belousova, E.A.b , Poujol, M.c 
On the edge: U-Pb, Lu-Hf, and Sm-Nd data suggests reworking of the Yilgarn craton margin during formation of the Albany-Fraser Orogen
(2011) Precambrian Research, 187 (3-4), pp. 223-247. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955738975&partnerID=40&md5=2838ed8f49d7c6c4248b76623132e298
AFFILIATIONS: Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia; 
GEMOC, Macquarie University, Sydney, NSW 2109, Australia; 
Géosciences Rennes UMR CNRS 6118, Université Rennes 1, 35042 Rennes Cedex, France
ABSTRACT: The Albany-Fraser Orogen is considered to be a response to Mesoproterozoic continent-continent collision between the combined North and West Australian Cratons and the combined East Antarctic and South Australian Cratons. However, the tectonic history of the orogen and its components remain enigmatic. Recently, the Kepa Kurl Booya Province has been defined as the crystalline basement of the orogen and divided into the Fraser, Biranup, and Nornalup Zones. New geochronology shows that the Biranup Zone includes 1710-1650. Ma granitic to gabbroic intrusions and is a substantial crustal component extending at least 1200. km along the southern and southeastern margins of the Yilgarn Craton. Previous models interpreted the Biranup Zone as an exotic terrane accreted to the Yilgarn Craton during Mesoproterozoic collision, but new data presented here indicate a strong link to the craton margin during the Paleoproterozoic. Proterozoic magmatism commenced in the Biranup Zone at 1708 ± 15. Ma with metasyenogranite emplacement. This granite has e{open}Hf values of -10 to -8 and whole rock e{open}Nd of -15, consistent with a reworked Archean Yilgarn source. Volcaniclastic deposition in the Biranup Zone occurred at 1689 ± 6. Ma, and was rapidly followed by granitic intrusion at 1686 ± 8. Ma. Deformation during the Zanthus Event is constrained by 1676 ± 6. Ma folded migmatitic leucosomes and 1679 ± 6. Ma cross-cutting axial planar leucosomes. A younger suite of granitic and gabbroic rocks, which exhibit distinct mingling and hybridization textures, is dated at 1665 ± 4. Ma. Magmatism in the eastern Biranup Zone displays high-K, calc-alkaline chemistry and a trend towards more juvenile compositions from 1710 to 1650. Ma. Based on the rapidly evolving tectonomagmatic history, modification of the original Yilgarn-like source by juvenile material, and the geochemical evolution of the melts, a feasible tectonic scenario for the Biranup Zone is an arc to back-arc setting on the active Yilgarn Craton margin. Such a model is supported by the 2684 ± 11. Ma magmatic crystallization age of an isolated Archean fragment, which has clear Yilgarn affinity, within the Biranup Zone. The region was subsequently compressed and tectonically dismembered during Stages I (1345-1260. Ma) and II (1215-1140. Ma) of the Albany-Fraser Orogeny. Stage I was dominated by voluminous mafic and granitic magmatism, represented by the Fraser Zone intrusions and the Recherche Supersuite. Two granites from the Fraser Zone, dated at 1298 ± 4. Ma, have e{open}Hf values overlapping Biranup Zone compositions, indicative of a reworked Biranup source. The Biranup Zone was dominated by granulite facies metamorphism during Stage II. Zircons from the northeastern edge of the Fraser Zone are overgrown by two generations of zircon rims. The earlier rims, at c. 1270 ± 11. Ma, are broken and overgrown by a low-uranium fracture-filling phase at 1193 ± 26. Ma. This indicates uplift and brittle deformation between Stages I and II. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Albany-Fraser Orogen;  Baddeleyite;  Biranup Zone;  Fraser Zone;  Lu-Hf;  Sm-Nd;  U-Pb;  Zircon
DOCUMENT TYPE: Article
SOURCE: Scopus

Esteban, F.a , Tassone, A.a , Menichetti, M.b , Rapalini, A.E.a , Remesal, M.B.c , Cerredo, M.E.c , Lippai, H.a , Vilas, J.F.a 
Magnetic fabric and microstructures across the Andes of Tierra del Fuego, Argentina [Fábrica Magnética y Microestructuras a través de los Andes de Tierra del Fuego, Argentina]
(2011) Andean Geology, 38 (1), pp. 64-81. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955701895&partnerID=40&md5=c0cfd5656871cf1a60fa6c1cd618cd15
AFFILIATIONS: CONICET-INGEODAV, Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, C1428EHA Ciudad Autónoma de Buenos Aires, Argentina; 
Istituto di Scienze della Terra, Università di Urbino, Campus Scientífico Universitario, 61029 Urbino, Italy; 
CONICET-Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, C1428EHA Ciudad Autónoma de Buenos Aires, Argentina
ABSTRACT: An anisotropy of magnetic susceptibility (AMS) transect was carried out across the Fuegian Andes, in Argentina, with the aim of studying its tectonic evolution. Two-hundred and forty oriented samples were collected from 27 sites distributed between the Paso Garibaldi to the north and the Canal Beagle to the south. The study was restricted to the Upper Jurassic Lemaire Formation, with a single site located in the Lower Cretaceous Yahgán Formation. Studied rocks comprised basaltic, andesitic, volcaniclastic and sedimentary rocks affected by low-grade metamorphism. AMS measurements were complemented with thin section analyses of representative samples in order to characterize the microstructures and metamorphic assemblages. In general, the magnetic fabric shows dominant oblate shapes and a large variation in the anisotropy degree from 1.04 up to 2. The anomalously high values were observed to be associated to growth of secondary pyrrhotite, which was identified by rock magnetic tests. Magnetic foliation was generally consistent with slaty cleaveage as observed in the field, confirming the tectonic origin of the magnetic fabric. Three geographic domains were distinguished in the study region on the basis of the pattern of the AMS axes distribution. In the northern domain, from Paso Garibaldi to Valle Carbajal, the orientation of the maximum susceptibility axis (k1), or magnetic lineation, is N-S to NE-SW with moderate plunge towards the S-SW and coincides with previous determination of mineral lineations associated with the Andean deformation and very low grade metamorphism. The magnetic fabric pattern can be correlated with the main deformational phase responsible for the development of slaty cleavage (main Andean deformational phase) and the tectonic transport due to progression of the Fuegian fold and thrust belt in the Late Cretaceous. A different character is shown along the Valle Carbajal domain, where subvertical E-W magnetic foliation planes and roughly E-W to ESE-WNW subhorizontal magnetic lineations are more difficult to correlate with the main folding phase and suggest its relation to an E-W, possibly localized, strike-slip regime during the main deformational and metamorphic phase. The magnetic fabrics in the third domain, close to the Canal Beagle, displays a more heterogeneous character with both E-W and N-S striking foliations; in this case a population of subhorizontal E-W magnetic lineation (k1) suggests the existence of a significant component of strike-slip deformation.
AUTHOR KEYWORDS: AMS;  Andean tectonics;  Argentina;  Mesozoic;  Microstructures;  Tierra del Fuego
DOCUMENT TYPE: Article
SOURCE: Scopus

Muravchik, M., D'Elia, L., Bilmes, A., Franzese, J.R.
Syn-eruptive/inter-eruptive relations in the syn-rift deposits of the Precuyano Cycle, Sierra de Chacaico, Neuquén Basin, Argentina
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955676312&partnerID=40&md5=03574d10d39cac06f5578f4f69b6e22b
AFFILIATIONS: Centro de Investigaciones Geológicas, Universidad Nacional de La Plata-CONICET, Calle 1 #644, B1900TAC, La Plata, Argentina
ABSTRACT: The syn-rift volcanic successions of the Upper Triassic-Lower Jurassic Precuyano Cycle (i.e. the Lapa Formation) from the Sierra de Chacaico in the Neuquén Basin, Argentina, were studied in order to address the distinctive characteristics of accumulation during syn-eruptive and inter-eruptive periods in a depocentre associated with active volcanism and extensional tectonics. In particular, the syn-rift fill in this area comprises a wide range of compositions, as well as of transport and depositional processes. Lava flows coexist with pyroclastic and epiclastic deposits in the same accumulation space. In order to analyse the complexities inherent in a volcanic environment subjected to extension, five different accumulation units were identified in the area: Lava Flow/Shallow Intrusion Units, Pyroclastic Units, Volcaniclastic Alluvial Units, Polymictic Alluvial Units, and Lacustrine Units. The analysis of each of these units and of the relationship between them provided meaningful insights into the evolution of the syn-rift sedimentary environments and the identification of different stages of effusive activity, explosive activity and relative quiescence, determining syn-eruptive and inter-eruptive rock units. The relationship between these units was examined, and two accumulation stages were defined. The underfilled stage originates when the material supplied to the depocentre during the eruptive events is not enough to level the existent topography, allowing the development of high-gradient alluvial systems during the next inter-eruptive period. The overfilled stage occurs when extensive pyroclastic density current deposits choke the accumulation space during syn-eruptive periods, causing low-gradient sedimentary systems to develop during the subsequent inter-eruptive periods. © 2011 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Inter-eruptive;  Neuquén Basin;  Syn-eruptive;  Syn-rift;  Volcanic rifts
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Nishiki, K.a , Takahashi, K.b , Matsumoto, A.a , Miyake, Y.c 
Quaternary volcanism and tectonic history of the Suwa-Yatsugatake Volcanic Province, Central Japan
Journal of Volcanology and Geothermal Research, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955550367&partnerID=40&md5=b0ce0e01c4ee11acba27eb06ed47b67d
AFFILIATIONS: Geological Survey of Japan (GSJ), AIST, Tsukuba Central 7th, 1-1-1, Higashi, Tsukuba, Ibaraki, 305-8567, Japan; 
Graduate School of Science and Technology, Shinshu University, 3-1-1, Asahi, Matsumoto, Nagano, 390-8621, Japan; 
Department of Geology, Faculty of Science, Shinshu University, 3-1-1, Asahi, Matsumoto, Nagano, 390-8621, Japan
ABSTRACT: Beneath central Japan, where three island arcs meet, the Pacific and Philippine Sea plates are both subducting, resulting in a complex tectonic history. The Suwa-Yatsugatake Volcanic Province (SYVP) consists of five groups of volcanoes (the Circum-Lake Suwa, Utsukushigahara, Kirigamine, Yabashira, and Yatsugatake volcanoes). The province is characterized by an enormous amount of volcanic activity, with lava flows and volcaniclastic rocks spread over a vast area of more than 1200 km2, and with a total eruption volume exceeding 400 km3. We determined the K-Ar ages of 41 samples of the SYVP with the aim of elucidating temporal and spatial changes in the tectonic and volcanic activities of central Japan. According to these new dates and previously reported radiogenic ages, we lead to conclude that volcanic activity has been occurring intermittently in the province since ca. 2.2 Ma. Volcanic activity in the SYVP can be classified into three phases, separated by dormant periods. Among these three phases, the volcanism during Phase II (1.6-0.7 Ma) is characteristic of an extensional stress field, such as voluminous outpourings of andesitic lava, and the existence of the WNW-ESE Oiwake Graben. Since ca. 5 Ma, Central Japan has been situated in a regional compressional stress field. However, in the SYVP, the stress field was locally extensional during Phase II. Here we propose a model in which the Izu Block, which lies above the Philippine Sea Plate, collided with Central Japan, resulting in enhanced NW-SE regional compressional stresses, but local extensional stresses in the SYVP due to the existence of a massive quantity of magma, and the geometry of the Itoigawa-Shizuoka Tectonic Line. We consider the volcanic activity in the SYVP to have been pulse-like, resulting from successive, intermittent collisions between Central Japan and blocks on the Philippine Sea Plate. © 2011 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: K-Ar ages;  Quaternary volcanism;  spatial and temporal changes;  Suwa-Yatsugatake Volcanic Province;  volcano-tectonic interactions
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Guo, Q.a  b , Xiao, W.a , Windley, B.F.c , Mao, Q.d , Han, C.a , Qu, J.a , Ao, S.a , Li, J.a  b , Song, D.a  b , Yong, Y.a 
Provenance and tectonic settings of Permian turbidites from the Beishan Mountains, NW China: Implications for the Late Paleozoic accretionary tectonics of the southern Altaids
Journal of Asian Earth Sciences, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955402253&partnerID=40&md5=9b46177f4118f78f3c783297175dd6a5
AFFILIATIONS: State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 
Graduate University of Chinese Academy of Sciences, Beijing 100049, China; 
Department of Geology, University of Leicester, Leicester LE1 7RH, UK; 
Beijing Institute of Geology for Mineral Resources, Beijing 100012, China
ABSTRACT: The Beishan orogenic belt, which connects the Tianshan suture on the west and Solonker suture on the east, contains key evidence for the termination time of the southern Altaids. Critical for evaluating different controversial tectonic models are Permian marine volcaniclastic arenites in the Liuyuan and Heishankou areas, which are dominated by greywackes and lenticular pebbly litharenites that contain grading, groove marks, and erosional bases, which provide evidence of turbidity action. Sandstones from the Liuyuan section are dominated by angular basaltic, andesitic, and feldspar fragments, but sandstones from the Heishankou section mainly consist of andesitic and felsic volcanic fragments. These relations suggest derivation from two different sources. Major element compositions suggest that the source rocks of the Heishankou litharenites were more SiO2-rich than those at Liuyuan. Sandstones at Heishankou are characterized by lower Ni-Co-Cr-V and slightly higher Th and La contents than those at Liuyuan. This indicates that the litharenites in the Liuyuan and Heishankou areas were derived from intermediate-mafic and intermediate-felsic source rocks, respectively. Tectonic setting discrimination plots suggest that the Liuyuan sandstones were deposited as detritus from an oceanic island arc, but the Heishankou sediments from an Andean continental margin. Our petrological and geochemical data from these two types of Permian turbidites suggest that an arc-continent collision took place in the Early Permian, and this is consistent with the Permian termination of the southern Altaids. © 2011 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Beishan Mountains;  Geochemistry;  Permian turbidites;  Provenance;  Southern Altaids;  Tectonic setting
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Amato, V.a , Aucelli, P.P.C.b , Cesarano, M.a , Pappone, G.b , Rosskopf, C.M.a , Ermolli, E.R.c  d 
The Sessano intra-montane basin: New multi-proxy data for the Quaternary evolution of the Molise sector of the Central-Southern Apennines (Italy)
(2011) Geomorphology, 128 (1-2), pp. 15-31. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952248193&partnerID=40&md5=a4e0ef31534eba85803d083026977a07
AFFILIATIONS: Dipartimento S.T.A.T., Università degli Studi del Molise, Contrada Fonte Lappone, 86090 Pesche (IS), Italy; 
Dipartimento DiSAm, Università degli Studi di Napoli Parthenope, Centro Direzionale, 80100 Napoli, Italy; 
Dipartimento di Arboricoltura Botanica e Patologia vegetale, Università di Napoli Federico II, Via Università 100, 80055 Portici (NA), Italy; 
Dept. de Prehistoire du Museum National d'Histoire Naturelle-USM103, MNHN-UMR7194, CNRS-Institut de Paleontologie Humaine, 1 rue René Panhard, 75013 Paris, France
ABSTRACT: An integrated geomorphological, geological-structural and stratigraphic approach was applied to the Sessano intra-montane basin (Molise, Central-Southern Apennines) to understand the Quaternary environmental and sedimentary evolution of the basin and the surrounding areas. The morpho-evolutionary and sedimentary changes were mainly controlled by tectonics and strongly influenced by the huge amount of volcaniclastic input from the Roccamonfina volcano (located ca. 50km to the south-west) as well as by climatic changes. Chronological constraints, supported by 40Ar/39Ar ages of tephra layers, archaeo-tephro-stratigraphy and pollen analysis, permit identification of the main phases of the geological-geomorphologic evolution of the Sessano basin from the Middle Pleistocene onwards. The sedimentation within the basin was controlled by NE-SW extensional tectonics and occurred from the end of Oxygen Isotope Stage (OIS) 15 to the beginning of OIS 11 allowing the deposition of ca. 85m of fluvial to lacustrine sediments, mainly made up of reworked volcaniclastic material. The first phase of sedimentation was lacustrine, while an important sedimentary change from lacustrine to fluvial-marshy environment occurred during OIS 14. After this phase, the variable input of volcaniclastic material from the Roccamonfina volcano together with climatic influences caused repeated changes from palustrine to fluvial sedimentation, and the formation of various palaeosols present mainly in the upper portion of the infill. Towards the end of OIS 11, NNW-SSE extensional tectonics caused the tilting of the fill succession and the drying up of the basin. The fill succession was then affected by fluvial erosion and denudation that generated an erosion surface nowadays hanging at 700-720m asl. This surface can be related to the limbs of a palaeo-surface at about 600m asl present in the adjacent Carpino-Le Piane intra-montane basin and referred to a fourth order, Tyrrhenian-ward oriented palaeo-landscape. This palaeo-landscape can be dated to ca. 350-300ky and, therefore, represents an important morpho-chronological stage. It provides a robust maximum and minimum age framework for reconstructing the geological and geomorphological evolution of the study area and, in general, of the Molise Apennines including the Boiano, Carpino-Le Piane and Sessano intra-montane basins. In particular, the morpho-chronological data from the Sessano basin allow us to date more precisely the main tectonic phases that occurred during the Middle Pleistocene in this sector of the Apennine chain. Finally, the multi-proxy data derived from the Sessano basin can be compared and integrated with those referring to other proximal intra-montane basins in order to improve our knowledge on the relationships between tectonics, volcanism and climate and the stratigraphic-sedimentary features, geomorphologic evolution and palaeoenvironmental changes that characterized the Central-Southern Apennines during Middle Pleistocene. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Central-Southern Apennines;  Extensional tectonic;  Intra-montane basins;  Palaeoenvironments;  Quaternary evolution;  Stratigraphy
DOCUMENT TYPE: Article
SOURCE: Scopus

Kwon, C.W.a , Jeong, J.O.b , Sohn, Y.K.a 
Sedimentary records of rift to pull-apart tectonics in the Miocene Eoil Basin, SE Korea
(2011) Sedimentary Geology, 236 (3-4), pp. 256-271. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952701724&partnerID=40&md5=fa055607bff7bbd5797a865d89d95ec8
AFFILIATIONS: Department of Earth and Environmental Sciences, Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, South Korea; 
Central Instrument Facility, Gyeongsang National University, Jinju 660-701, South Korea
ABSTRACT: The Miocene Eoil Basin, SE Korea, is a pull-apart basin formed by dextral crustal deformation during the backarc opening of the East Sea. The Gampo Conglomerate, the lowermost formation of the basin, provides significant information on how a pull-apart basin initiates and is filled by sedimentary strata. The formation consists of nonmarine conglomerates, sandstones, mudstones, and a variety of volcaniclastic deposits that were deposited in alluvial fans, delta slopes, braided streams, mouth bars, and lakes. These deposits are organized into several stratal packages (SP) with contrasting geometries. SP I at the base consists of mouth-bar to delta-front and volcaniclastic deposits, and shows rapid facies variations along the southeastern normal fault margins. SP I suggests that the early basin was bounded by multiple, incipiently developed normal faults with variable displacement and accommodation creation. SP II consists of thick alluvial-fan conglomerates and overlies SP I abruptly, suggesting sudden input of coarse-grained sediment from the uplifted footwalls. It is thickest near the central part of the southeastern normal fault margins, suggesting development of a large alluvial fan near a transfer zone. SP III consists mostly of mouth-bar sandstones, indicating abrupt subsidence of the basin and the transition from subaerial to subaqueous environments. SP IV consists of braided-stream conglomerates, suggesting gradual progradation of coarse-grained fluvial systems toward the basin when the extension and subsidence of the basin was slowed. SP V shows upward-deepening facies changes from braided-stream to mouth-bar deposits, suggesting resumption of basin subsidence. Notably, the cumulative thickness of SP III to SP V is thickest near the northeastern and southwestern strike-slip margins, suggesting migration of the loci of maximum subsidence from the normal fault margins towards the strike-slip margins after deposition of SP II. The change in stratal architecture suggests that the activity of the normal faults was dominant in the early stage of the basin evolution whereas the activity of the strike-slip faults became more pronounced afterwards. Overall, the stratal architecture of the Gampo Conglomerate appears to record the transition tectonics from rift to pull-apart during the incipient stage of a pull-apart basin development. The Eoil Basin is thus interpreted to have been hybrid in nature, influenced by the dynamic changes of the basin-margin faults, which were either normal or strike-slip. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Basin evolution;  Eoil Basin;  Gampo Conglomerate;  Pull-apart basin;  Stratigraphic development
DOCUMENT TYPE: Article
SOURCE: Scopus

Stiegler, M.T.a , Lowe, D.R.a , Byerly, G.R.b 
Fragmentation and dispersal of komatiitic pyroclasts in the 3.5-3.2 Ga Onverwacht group, Barberton greenstone belt, South Africa
(2011) Bulletin of the Geological Society of America, 123 (5), pp. 1112-1126. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953803436&partnerID=40&md5=ef932578b1459748f0eaf140c89ce1bf
AFFILIATIONS: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, United States; 
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, United States
ABSTRACT: The 3.5-3.2 Ga Onverwacht Group of the Barberton greenstone belt, South Africa, contains thick sequences of komatiitic tuff, lapilli tuff, and lapillistone representing proximal to distal volcanic settings. Volcaniclastic komatiites in the southern part of the belt include: (1) areally extensive sheets of silicified, massive to normally graded ash and accretionary lapilli interpreted as pyroclastic fall deposits, and (2) thick, widespread, carbonatized beds of lapilli and minor ash deposited by subaqueous sediment flow and pyroclastic fallout. Lithofacies 1 clasts are aphyric and poorly to nonvesicular, implying rapid quench rates and fragmentation primarily through magma-water contact. Low water/magma ratios, initial melt fracturing through minor volatile exsolution, and high magma fluxes were probably the main factors that enabled the production of buoyant eruption columns and widespread ash distribution. These tuffs were generated during vent shoaling in water that was probably <10 m deep and were preferentially preserved in distal settings on komatiitic platforms. Lithofacies 2 contains both coarse, blocky microphyric and porphyritic grains indicative of low-energy hydroclastic fragmentation and fluidal, ragged clasts formed during vigorous subaqueous explosions. These were deposited mainly in proximal to medial settings prior to vent emergence. In the northern part of the belt, 2-60-m-thick sections of serpentinized, fine-grained komatiitic tuff were deposited by pyroclastic fallout into subaqueous environments and were widely reworked by moderate- to low-energy currents. Komatiites throughout the Onverwacht Group were produced in multivent volcanic fields in marine settings that were starved of clastic input, making explosive komatiitic volcanism one of the main sediment-generating processes. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Sorrentino, L., Cas, R.A.F., Stilwell, J.D.
Evolution and facies architecture of Paleogene Surtseyan volcanoes on Chatham Islands, New Zealand, Southwest Pacific Ocean
(2011) Journal of Volcanology and Geothermal Research, 202 (1-2), pp. 1-21. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953164662&partnerID=40&md5=981d4825e7f134084dcec4ef932fce2f
AFFILIATIONS: School of Geosciences, Monash University, Australia
ABSTRACT: This paper reports for the first time phreatomagmatic deposits and preserved Surtseyan tuff cones in the Chatham Islands, New Zealand. Fieldwork has located the relicts of at least six, closely-spaced, Paleogene Surtseyan-cones and associated volcaniclastic sediments within the Red Bluff Tuff Formation. The complete stratigraphic section of the cones consists of two parts: 1) the lower part represents volcanic aggradational processes that constructed tuff cones in a short period of time, and is composed of a bedded interval of explosively fragmented, vesicular glassy basaltic pyroclasts (ash and lapilli sizes) as well as feeder-dykes, pillow-lavas and pillow-sills and 2) the upper part represents the rapid denudation of these cones by shallow marine currents or gravity-flows reflecting the instability of the tephra-pile forming the cones, and a much later marine faunal colonization stage (e.g. corals, brachiopods, molluscs, etc.). Erosion could have occurred almost immediately after (or even during) the emplacement of the volcanic pile, similar to what occurred at Surtla vent, a satellite submerged cone of the basaltic island volcano Surtsey, Iceland; the Waiareka-Deborah Volcanics Bridge Point, Aorere Point, and Lookout Bluff Surtseyan-cones (Otago, New Zealand); and Marion and Prince Edward islands (Southwest Indian Ocean), amongst others. By contrast, the complete faunal colonization and stabilization of a diverse marine community could have taken hundreds, or perhaps even thousands of years to reach their acme following the volcanic pulses. The structural, textural and compositional characteristics of the Red Bluff Tuff Formation support a phreatomagmatic mode of fragmentation similar to that at Surtsey Volcano, Iceland. The Red Bluff Tuff sequence represents one of the most complete marine tuff cones described in the geologic record. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Basaltic;  Chatham Island;  Phreatomagmatic;  Pyroclastic surge;  Surtseyan;  Tuff cones
DOCUMENT TYPE: Article
SOURCE: Scopus

Belousov, A.a , Behncke, B.a  b , Belousova, M.a  c 
Generation of pyroclastic flows by explosive interaction of lava flows with ice/water-saturated substrate
(2011) Journal of Volcanology and Geothermal Research, 202 (1-2), pp. 60-72. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953163717&partnerID=40&md5=26d93e2e5b21c1093cec14261ec766a2
AFFILIATIONS: Earth Observatory of Singapore, Nanyang Technological University, Singapore; 
Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, Italy; 
Institute of Volcanology and Seismology, Petropavlovsk, Russian Federation
ABSTRACT: We describe a new type of secondary rootless phreatomagmatic explosions observed at active lava flows at volcanoes Klyuchevskoy (Russia) and Etna (Italy). The explosions occurred at considerable (up to 5 km) distances from primary volcanic vents, generally at steep (15-35°) slopes, and in places where incandescent basaltic or basaltic-andesitic lava propagated over ice/water-saturated substrate. The explosions produced high (up to 7 km) vertical ash/steam-laden clouds as well as pyroclastic flows that traveled up to 2 km downslope. Individual lobes of the pyroclastic flow deposits were up to 2 m thick, had steep lateral margins, and were composed of angular to subrounded bomb-size clasts in a poorly sorted ash-lapilli matrix. Character of the juvenile rock clasts in the pyroclastic flows (poorly vesiculated with chilled and fractured cauliflower outer surfaces) indicated their origin by explosive fragmentation of lava due to contact with external water. Non-juvenile rocks derived from the substrate of the lava flows comprised up to 75% in some of the pyroclastic flow deposits. We suggest a model where gradual heating of a water-saturated substrate under the advancing lava flow elevates pore pressure and thus reduces basal friction (in the case of frozen substrate water is initially formed by thawing of the substrate along the contact with lava). On steep slope this leads to gravitational instability and sliding of a part of the active lava flow and water-saturated substrate. The sliding lava and substrate disintegrate and intermix, triggering explosive "fuel-coolant" type interaction that produces large volume of fine-grained clastic material. Relatively cold steam-laden cloud of the phreatomagmatic explosion has limited capacity to transport upward the produced clastic material, thus part of it descends downslope in the form of pyroclastic flow. Similar explosive events were described for active lava flows of Llaima (Chile), Pavlof (Alaska), and Hekla (Iceland) indicating that this type of explosions and related hazard is common at snow/ice-clad volcanoes and sometimes happens also on fluid-saturated hydrothermally altered slopes. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Etna;  Klyuchevskoy;  Lava flow;  Phreatomagmatic explosion;  Pyroclastic flow;  Secondary explosion
DOCUMENT TYPE: Article
SOURCE: Scopus

Tagiri, M.a , Dunkley, D.J.b , Adachi, T.c , Hiroi, Y.d , Fanning, C.M.e 
SHRIMP dating of magmatism in the Hitachi metamorphic terrane, Abukuma Belt, Japan: Evidence for a Cambrian volcanic arc
Island Arc, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955135454&partnerID=40&md5=92c951f5b887e2a2b118be9c55f5088b
AFFILIATIONS: Hitachi City Museum, Miyatacho 5-2-22, Hitachi 317-0055, Japan.; 
National Institute of Polar Research, Midori-cho 10-3, Tachikawa 190-8518, Japan.; 
Graduate School of Social and Cultural Studies, Kyushu University, Motooka 744, Nishiku, Fukuoka 819-0395, Japan.; 
Department of Earth Sciences, Chiba University, Yayoi-cho 1-33, Inageku, Chiba 263-8522, Japan.; 
Research School of Earth Sciences, The Australian National University, Canberra 0200 ACT, Australia.
ABSTRACT: Ion microprobe dating of zircon from meta-igneous samples of the Hitachi metamorphic terrane of eastern Japan yields Cambrian magmatic ages. Tuffaceous schist from the Nishidohira Formation contains ca 510Ma zircon, overlapping in age with hornblende gneiss from the Tamadare Formation (ca 507Ma), and meta-andesite (ca 507Ma) and metaporphyry (ca 505Ma) from the Akazawa Formation. The latter is unconformably overlain by the Carboniferous Daioin Formation, in which a granite boulder from metaconglomerate yields a magmatic age of ca 500Ma. This date overlaps a previous estimate for granite that intrudes the Akazawa Formation. Intrusive, volcanic, and volcaniclastic lithologies are products of a Cambrian volcanic arc associated with a continental shelf, as demonstrated by the presence of arkose and conglomerate in the lowermost Nishidohira Formation. Granitic magmatism of Cambrian age is unknown elsewhere in Japan, except for a single locality in far western Japan with a similar geological context. Such magmatism is also unknown on the adjacent Asian continental margin, with the exception of the Khanka block in far northeastern China. A 'great hiatus' in the Paleozoic stratigraphy of the Sino-Korean block also exists in the Hitachi terrane between Cambrian volcanic arc rocks and Early Carboniferous conglomerate, and may indicate a common paleogeographic provenance. © 2011 Blackwell Publishing Asia Pty Ltd.
AUTHOR KEYWORDS: Abukuma Belt;  Cambrian volcanic arc;  Hitachi metamorphic terrane;  North China block;  SHRIMP zircon age;  Unconformity
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Perriello Zampelli, S.a , Bellucci Sessa, E.b , Cavallaro, M.a 
Application of a GIS-aided method for the assessment of volcaniclastic soil sliding susceptibility to sample areas of Campania (Southern Italy)
(2011) Natural Hazards, pp. 1-14. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955122401&partnerID=40&md5=a744b70211ab5317e850cc992e7641be
AFFILIATIONS: Dipartimento di Scienze della Terra, Università di Napoli Federico II, Naples, Italy; 
Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Vesuviano, Naples, Italy
ABSTRACT: A significant part of Campania is extensively covered by volcaniclastic soils, deriving from the alteration of airfall-sedimented formations of layered ashes and pumices that were ejected by Campi Flegrei and Mt. Somma-Vesuvius during explosive eruptions. Where such soils cover steep slopes cut in carbonate bedrock, landforms depend essentially on the morpho-evolution of such slopes prior to the deposition of the volcaniclastic soils, because these are generally present only as thin veneers, up to a few meters of total thickness. Historical records and local literature testify that, in this part of Campania, landslides that originate on carbonate slopes covered by such soils and terminate at their foot or at gully outlets are frequent, following critical rainfall events. Such landslides can be classified as complex, occurring initially as debris slides, but rapidly evolving into debris avalanches and/or debris flows. The localization of the initial sliding areas (i.e. "sources") on the slopes depends on both the spatial distribution of characters of the soil cover and the spatial distribution of the triggering rainfall events. It therefore appears reasonable to separate the two aspects of the problem and focus on the former one, in order to attempt an assessment of soil sliding susceptibility in the event of landslide-triggering rainfall. In this paper, some results of the application of a method aimed at such an assessment are presented. The method, called SLIDE (from SLiding Initiation areas DEtection), is based on the concept that, for a spatially homogeneous soil cover and a spatially homogeneous landslide-triggering rainfall sequence, different values of threshold slope gradient for limit equilibrium conditions exist, depending on morphological characters of the soil cover, such as its continuity and planform curvature. The method is based on the assessment of (1) soil cover presence, (2) discontinuities within soil cover, (3) slope gradients and curvature, by means of good resolution DEMs. It has been applied to sample carbonate slopes of Campania, where landslides originated either repeatedly or recently. Results are encouraging, and a soil sliding susceptibility map of a large area, based on a simplified version of method, is also presented. © 2011 Springer Science+Business Media B.V.
AUTHOR KEYWORDS: Debris-slide susceptibility;  Planform curvature;  Soil cover discontinuities;  Volcaniclastic soil cover
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Kralj, P.
Eruptive and sedimentary evolution of the Pliocene Grad Volcanic Field, North-east Slovenia
(2011) Journal of Volcanology and Geothermal Research, 201 (1-4), pp. 272-284. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953043390&partnerID=40&md5=09cade4e48a85aa8b7c4329bd16b52e3
AFFILIATIONS: Geological Survey of Slovenia, Dimiceva 14, SI-1000 Ljubljana, Slovenia
ABSTRACT: Middle to Upper Pliocene (~3Ma) Grad Volcanic Field (SW Pannonian basin system) encompasses an area of about 3km2, of which some 1.7km2 belong to the outcropping volcanics. Pyroclastic and syn-eruptively reworked volcaniclastic deposits are the most widespread in occurrence. Remains of an autobrecciated lava flow, a residual neck and their peperites are partially reworked by a large debris flow. Volcanic activity occurred in a continental depositional environment dominated by alluvial fan and braided river systems. Streams draining from the north-west to the south-east were infilling a rapidly subsiding Radgona Depression. The style of volcanic activity was mainly explosive and was reinforced by hydrovolcanic processes. Three volcanic centres probably existed, and they migrated spatially and temporally from the north to the south over a distance of some 5.6. km. The rocks of the northernmost volcanic centre are fairly eroded and contain abundant, up to 10. cm sized lherzolite xenoliths. The largest crater developed about 2.5. km to the south. From an early maar stage, a tuff-cone, and subsequently, a tuff-ring evolved. The crater was filled with eroded pyroclastic material and stream load. A new vent became active some 500. m to the south. Initial stage was mainly magmatic and produced pyroclastic flow and fall deposits. Late-stage eruptions were predominantly hydrovolcanic (phreatomagmatic and phreatic), and built up a small tuff-cone having some 300. m in diameter. Trachybasaltic and subordinate basanitic magmas erupting in the Grad Volcanic Field are geochemically distinguishable from the neighbouring occurrences in the South Styrian Basin and the South Burgenland Swell. Relatively lower abundance of TiO2, MgO, Sc, V and Cu, and higher abundance of MnO, P2O5, Zn, Sr, Zr, Hf, Nb, Ba, Ta and U indicate somewhat different source and/or evolutionary pattern. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Alkaline basaltic volcanism;  Maar deposits;  Reworked volcaniclastic deposits;  Tuff-ring deposits
DOCUMENT TYPE: Article
SOURCE: Scopus

Seghedi, I.
Permian rhyolitic volcanism, changing from subaqueous to subaerial in post-Variscan intra-continental Sirinia Basin (SW Romania-Eastern Europe)
(2011) Journal of Volcanology and Geothermal Research, 201 (1-4), pp. 312-324. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953041733&partnerID=40&md5=e53524f033a92da10ad807bb3c5db028
AFFILIATIONS: Institute of Geodynamics, Romanian Academy 19-21, Jean-Luis Calderon str., Bucharest 020032, Romania
ABSTRACT: The Sirinia Basin is a well-exposed, Upper Carboniferous-Lower Permian intra-continental extensional basin, containing 1-2. km of Permian interbedded terrigeneous sediments and primary volcanic and volcaniclastic rocks of rhyolitic composition. These are mostly the products of subaqueous volcanism passing into a subaerial volcanism. The intra-continental basin lies on the Danubian metamorphic units in the south westernmost part of the Carpathians (SW Romania) and is N-S oriented (18 × 8. km), as result of Alpine tectonic evolution and deformation. The Sirinia Basin setting formed a dynamic closed intra-continental sedimentary system that experienced a successive subsidence; it started with lacustrine sediments and then with large volumes of rhyolitic volcanic and volcaniclastic material dominantly sited in the central part of the basin. Volcanism included (1) subaqueous extrusion of domes surrounded by hyaloclastite deposits closely associated with secondary sedimentation, (2) extrusive and explosive Surtseyan-type and subaerial eruptions from shallow water to emergent volcanoes on dome-cap and associated reworked deposits, towards the southern side of the basin, and (3) subaerial extrusive domes. Fluvial erosion and deposition completed the evolution of the emerged marginal part of the basin. Most of the erupted material of the first and second phase filling the central part of the basin along extensional normal faults was rapidly transported on sides of the basin by turbidite sedimentation, debris flows, slumping and sliding. While turbidites prevail toward the central part of the basin, the debris flow sedimentation predominated at the margin of the basin, infrequently interrupted by deposition of fallout ash from hydromagmatic explosive eruptions related to the dome-cap tuff and pumice cones. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Debris flow;  Hyaloclastite;  Hydromagmatic;  Lower Permian;  Rhyolite domes;  Turbidite
DOCUMENT TYPE: Article
SOURCE: Scopus

Ross, P.-S.a , Delpit, S.a , Haller, M.J.b , Németh, K.c , Corbella, H.d 
Influence of the substrate on maar-diatreme volcanoes - An example of a mixed setting from the Pali Aike volcanic field, Argentina
(2011) Journal of Volcanology and Geothermal Research, 201 (1-4), pp. 253-271. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953040914&partnerID=40&md5=b5118e93fbb3a8308d57699f89c32641
AFFILIATIONS: Institut national de la recherche scientifique, 490 rue de la Couronne, Québec (QC), G1K 9A9, Canada; 
CentroUniversidad Nacional Patagónico-UNPSJBde la Patagonia San Juan Bosco-CONICET, Avda. Boulevard Brown 35003700, (9120) Puerto Madryn Chubut, Argentina; 
Volcanic Risk Solutions, Massey University, Private Bag 11 222, Palmerston North, New Zealand; 
Museo Argentino de Ciencias Naturales, Avenida Angel Gallardo 470, Buenos Aires, Argentina
ABSTRACT: The morphologic parameters, pyroclastic deposits and evolution of maar-diatreme volcanoes are affected by the type of environment in which they are emplaced. End-member cases are a hard substrate (rocks) and a soft substrate (unconsolidated volcaniclastic or sedimentary deposits). In this paper, we present an example of a volcanic complex emplaced in a mixed hard-soft setting from the Pali Aike volcanic field (PAVF) near the Argentina-Chile border. The Plio-Pleistocene PAVF is an alkaline, mafic, back-arc monogenetic field which contains over 100 phreatomagmatic volcanoes. The studied volcanic complex contains two large coalescent maars overlain by scoria and spatter. The 1.4 × 1.3. km East Maar has better exposures than the shallower, 1.9. km-wide West Maar and seems to have been less modified by post-eruptive processes. The tephra rim of the East Maar was studied in detail and we infer it was produced mostly by base surges from phreatomagmatic eruption columns, with rare instances of intercalated scoria fall layers. Based on regional information, the general pre-maar stratigraphy is dominated by sedimentary and volcaniclastic rocks of the Magallanes Basin, including a thick poorly consolidated upper unit dating from the Miocene. These are overlain by Plio-Pleistocene fluvio-glacial deposits and PAVF lavas, some of which are exposed in the East Maar just below the phreatomagmatic deposits. All of these units are represented as lithic clasts in the tephra rim of the East Maar, the most abundant being the clasts from the earlier basaltic lavas and rock fragments derived from the glacial deposits. There is no specific evidence for a deep diatreme under the East Maar, and in this particular case, the mixed environment seems to have produced a maar-diatreme volcano typical of a soft substrate. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Argentina;  Hard substrate;  Maar;  Phreatomagmatism;  Soft substrate
DOCUMENT TYPE: Article
SOURCE: Scopus

Gebhardt, A.C.a , De Batist, M.b , Niessen, F.a , Anselmetti, F.S.c , Ariztegui, D.d , Haberzettl, T.e , Kopsch, C.f , Ohlendorf, C.g , Zolitschka, B.g 
Deciphering lake and maar geometries from seismic refraction and reflection surveys in Laguna Potrok Aike (southern Patagonia, Argentina)
(2011) Journal of Volcanology and Geothermal Research, 201 (1-4), pp. 357-363. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953048051&partnerID=40&md5=c51e3e6b4c46de0206390d9549d785ed
AFFILIATIONS: Alfred Wegener Institute for Polar and Marine Research, 27568 Bremerhaven, Germany; 
Renard Centre of Marine Geology, University of Gent, 9000 Gent, Belgium; 
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters, 8600 Dübendorf, Switzerland; 
Section of Earth and Environmental Sciences, University of Geneva, 1205 Geneva, Switzerland; 
Institute of Geography, Friedrich-Schiller-University Jena, 07743 Jena, Germany; 
Alfred Wegener Institute for Polar and Marine Research, 14473 Potsdam, Germany; 
Institute of Geography, University of Bremen, 28359 Bremen, Germany
ABSTRACT: Laguna Potrok Aike is a bowl-shaped maar lake in southern Patagonia, Argentina, with a present mean diameter of ~3.5km and a maximum water depth of ~100m. Seismic surveys were carried out between 2003 and 2005 in order to get a deeper knowledge on the lake sediments and the deeper basin geometries. A raytracing model of the Laguna Potrok Aike basin was calculated based on refraction data while sparker data were additionally used to identify the crater-wall discordance and thus the upper outer shape of the maar structure. The combined data sets show a rather steep funnel-shaped structure embedded in the surrounding Santa Cruz Formation that resembles other well-known maar structures. The infill consists of up to 370m lacustrine sediments underlain by probably volcanoclastic sediments of unknown thickness. The lacustrine sediments show a subdivision into two sub-units: (a) the upper with seismic velocities between 1500 and 1800ms-1, interpreted as unconsolidated muds, and (b) the lower with higher seismic velocities of up to 2350ms-1, interpreted as lacustrine sediments intercalated with mass transport deposits of different lithology and/or coarser-grained sediments. The postulated volcanoclastic layer has acoustic velocities of &gt;2400ms-1. The lake sediments were recently drilled within the PASADO project in the framework of the International Continental Scientific Drilling Program (ICDP). Cores penetrated through lacustrine unconsolidated sediments down to a depth of ~100m below lake floor. This minimal thickness for the unconsolidated and low-velocity lithologies is in good agreement with our raytracing model. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Explosive volcanism;  Maars;  PASADO project;  Sedimentary basin processes;  South America
DOCUMENT TYPE: Article
SOURCE: Scopus

Porritt, L.A., Russell, J.K.
Kimberlite ash: Fact or fiction
Physics and Chemistry of the Earth, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953651387&partnerID=40&md5=7f04a1b25038ee22325d6f63b262fb11
AFFILIATIONS: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, Canada
ABSTRACT: Kimberlite pipes represent the conduits and vents of eroded volcanoes and are commonly filled with both coherent and volcaniclastic kimberlite including pyroclastic deposits, resulting from explosive volcanic eruptions. The properties of pyroclastic deposits, including grain size and grain shape distributions of pyroclasts, provide insight into the intensity and style of explosive volcanic eruptions. Pyroclastic kimberlite deposits generally comprise abundant coarse (>5 mm) crystals and juvenile and country rock lapilli within a matrix of serpentine and other minerals interpreted to be late-stage alteration products. A consequence of the late-stage alteration processes affecting most kimberlite is that there is substantial textural ambiguity in the interpretation of the ash-sized pyroclast fraction. For example, vitric ash is never directly observed. It is presently unknown whether vitric ash is: (i) simply not produced, (ii) completely removed from the system prior to deposition, or (iii) incorporated into the deposits and then subsequently overprinted by alteration. The presence or absence of fine ash within these deposits greatly affects pyroclast size distributions and, therefore, has substantial implications on the nature and energetics of magma fragmentation and eruption processes. Our analysis suggests that explosive kimberlite eruptions can be expected to commonly produce fine ash. Deposits that preserve ash-sized mineral grains, lithic fragments, and coarse ash-sized juvenile clasts provide direct evidence for the intensity and style of kimberlite eruption. Our calculations of glass transition temperatures and melt relaxation timescales relative to rates of cooling and crystallization of pyroclasts show that vitric kimberlitic ash can only be produced by high intensity eruptions with extremely rapid cooling. © 2011 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Eruption;  Glass transition;  Kimberlite;  Vitric ash
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Lenhardt, N.a  b , Hornung, J.a , Hinderer, M.a , Böhnel, H.c , Torres-Alvarado, I.S.d , Trauth, N.a 
Build-up and depositional dynamics of an arc front volcaniclastic complex: The Miocene Tepoztlán Formation (Transmexican Volcanic Belt, Central Mexico)
(2011) Sedimentology, 58 (3), pp. 785-823. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952642139&partnerID=40&md5=bc98d4ccc8205cbd8ea841020af7c96b
AFFILIATIONS: Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Darmstadt, Germany; 
Department of Geology, University of Pretoria, Pretoria, South Africa; 
Centro de Geociencias, Universidad Nacional Autónoma de México, Queretaro, Mexico; 
Centro de Investigacíones en Energía, Universidad Nacional Autónoma de México, Temixco, Mexico
ABSTRACT: Volcanic terrains such as magmatic arcs are thought to display the most complex surface environments on Earth. Ancient volcaniclastics are notoriously difficult to interpret as they describe the interplay between a single or several volcanoes and the environment. The Early Miocene Tepoztlán Formation at the southern edge of the Transmexican Volcanic Belt belongs to the few remnants of this ancestral magmatic arc, and therefore is thought to represent an example of the initial phase of evolution of the Transmexican Volcanic Belt. Based on geological mapping, detailed logging of lithostratigraphic sections, palaeocurrent data of sedimentary features and anisotropy of magnetic susceptibility, mapping of two-dimensional panels from outcrop to field scale, and geochronological data in an area of ca 1000km2, three periods in the evolution of the Tepoztlán Formation were distinguished, which lasted around 4Myr and are representative of a volcanic cycle (edifice growth phases followed by collapse) in a magmatic arc setting. The volcaniclastic sediments accumulated in proximal to medial distances on partly coalescing aprons, similar to volcanic ring plains, around at least three different stratovolcanoes. These volcanoes resulted from various eruptions separated by repose periods. During the first phase of the evolution of the Tepoztlán Formation (22·8 to 22·2Ma), deposition was dominated by fluvial sediments in a braided river setting. Pyroclastic material from small, andesitic-dacitic composite volcanoes in the near vicinity was mostly eroded and reworked by fluvial processes, resulting in sediments ranging from cross-bedded sand to an aggradational series of river gravels. The second phase (22·2 to 21·3Ma) was characterized by periods of strong volcanic activity, resulting in voluminous accumulations of lava and tuff, which temporarily overloaded and buried the original fluvial system with its detritus. Continuous build-up of at least three major volcanic centres further accentuated the topography and, in the third phase (21·3 to 18·8Ma), mass flow processes, represented by an increase of debris flow deposits, became dominant, marking a period of edifice destruction and flank failures. © 2010 The Authors. Journal compilation © 2010 International Association of Sedimentologists.
AUTHOR KEYWORDS: Facies model;  Lithofacies analysis;  Miocene;  Transmexican Volcanic Belt;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Gibert, L.a , Alfaro, P.b , García-Tortosa, F.J.c , Scott, G.a 
Superposed deformed beds produced by single earthquakes (Tecopa Basin, California): Insights into paleoseismology
(2011) Sedimentary Geology, 235 (3-4), pp. 148-159. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952441213&partnerID=40&md5=c7382f7463737638b66223d261e9e4c9
AFFILIATIONS: Berkeley Geochronology Center, 2455 Ridge Road, 94709, Berkeley, CA, United States; 
Dpto. Ciencias de la Tierra y del Medio Ambiente Facultad de Ciencias, Universidad de Alicante, 03080 Alicante, Spain; 
Dpto. Geología, Facultad de Ciencias, Universidad de Jaén, Campus Las Lagunillas, 23071 Jaén, Spain
ABSTRACT: Well-exposed soft-sediment deformation (SSD) structures occur in Tecopa paleolake beds largely composed of ash from the Bishop (760. kyr) and the Lava Creek (640. kyr) ultra-plinian eruptions. In both cases the SSD structures affected volcaniclastic deposits concentrated by overland flow from the surrounding topography into the lower slope and lake environments. Re-sedimentation of ash produced alternations of volcaniclastic layers with different grain sizes and ash content that allowed for reverse density gradients, which favoured liquefaction and deformation. In the Tecopa Basin, extensive outcrops show these deformed strata continuing laterally for hundreds of metres, along with three-dimensional exposures. This study illustrates the 3-D complexity of soft-sediment deformation including some novel morphologic features. Of particular interest were examples of superposed deformed beds that laterally change into one single deformed horizon. Heterogeneities in ash concentration, grain-size, and water content produced contrasting permeabilities that were barriers to liquefaction and soft-sediment deformation. The probable causes for liquefaction were Middle Pleistocene paleo-earthquakes. There are several active faults in the region with enough seismic potential to produce moderate to large earthquakes. The fact that a single deformed deposit laterally merges into multiple superposed deformed beds indicates that multilayer liquefaction could be produced by a single shaking event. In these cases, SSD layers are insufficient and unreliable indicators of paleo-seismic recurrence intervals. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Earthquakes;  Liquefaction;  Load structures;  Seismites;  Soft-sediment deformation structures;  Tecopa Basin
DOCUMENT TYPE: Article
SOURCE: Scopus

Jones, M.T.a  e , Hembury, D.J.a , Palmer, M.R.a , Tonge, B.b , Darling, W.G.c , Loughlin, S.C.d 
The weathering and element fluxes from active volcanoes to the oceans: A Montserrat case study
(2011) Bulletin of Volcanology, 73 (3), pp. 207-222. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955701695&partnerID=40&md5=779f03a82317a624c6e7c6b763cb73a9
AFFILIATIONS: School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, Southampton SO14 3ZH, United Kingdom; 
Montserrat Water Authority, P.O. Box 324, Davy Hill, Montserrat; 
British Geological Survey, Maclean Building, Wallingford, Oxon OX10 8BB, United Kingdom; 
British Geological Survey, West Mains Road, Edinburgh EH9 3LA, United Kingdom; 
LMTG, UMR CNRS 5563, Université Paul-Sabatier, Observatoire Midi-Pyrénées, 14, avenue Edouard Belin, 31400 Toulouse, France
ABSTRACT: The eruptions of the Soufrière Hills volcano on Montserrat (Lesser Antilles) from 1995 to present have draped parts of the island in fresh volcaniclastic deposits. Volcanic islands such as Montserrat are an important component of global weathering fluxes, due to high relief and runoff and high chemical and physical weathering rates of fresh volcaniclastic material. We examine the impact of the recent volcanism on the geochemistry of pre-existing hydrological systems and demonstrate that the initial chemical weathering yield of fresh volcanic material is higher than that from older deposits within the Lesser Antilles arc. The silicate weathering may have consumed 1.3% of the early CO2 emissions from the Soufrière Hills volcano. In contrast, extinct volcanic edifices such as the Centre Hills in central Montserrat are a net sink for atmospheric CO2 due to continued elevated weathering rates relative to continental silicate rock weathering. The role of an arc volcano as a source or sink for atmospheric CO2 is therefore critically dependent on the stage it occupies in its life cycle, changing from a net source to a net sink as the eruptive activity wanes. While the onset of the eruption has had a profound effect on the groundwater around the Soufrière Hills center, the geochemistry of springs in the Centre Hills 5 km to the north appear unaffected by the recent volcanism. This has implications for the potential risk, or lack thereof, of contamination of potable water supplies for the island's inhabitants. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: CO2 sequestration;  Geochemistry;  Hydrology;  Montserrat;  Silicate weathering;  Soufrière Hills volcano
DOCUMENT TYPE: Article
SOURCE: Scopus

Benzaggagh, M.
Submarine volcanism activities at the Jurassic-Cretaceous boundary in the external Rif chain (Morocco). Age and relationship with sedimentation and the palaeogeography of the external riffian trough [Activitè s volcaniques sous-marines à la limite Jurassique-Crè tacè dansle Rif externe (Maroc). Â ge et relation avec la sèdimentatioetlapalèogèographiedu sillon rifain externe]
(2011) Comptes Rendus - Geoscience, 343 (4), pp. 302-311. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955043495&partnerID=40&md5=243b6f1f1c8663b8715f9e924b314408
AFFILIATIONS: Universite Moulay Ismail, Faculte des sciences, Departement de geologie, Beni M'Hamed, Meknès, Morocco
ABSTRACT: Following the recent stratigraphic works carried out on the Jurassic-Cretaceous boundary in the external Rif chain (Mesorif area and Bou Haddoud nappe), numerous submarine volcanism traces have been discovered in Upper Oxfordian to Upper Berriasian deposits. These traces display various aspects: volcaniclastic complexes incorporated within Upper Berriasian marls; volcanic lavas and basalt clasts included in the breccias with clay matrix of Upper Oxfordian to Lower Berriasian age, or in brecciated Lower Tothonian calcareous beds of the Early Tithonian. These submarine volcanic activities took place in a carbonate platform environment during the Kimmeridgian to Early Tithonian interval or in a pelagic basin from Late Tithonian onwards. They caused an intense brecciation of Upper Jurassic carbonate formations and a general dismantling of marly calcareous alternations of Upper Tithonian-Lower Berriasian. Therefore, the Upper Tithonian-Lower Berriasian deposits are marked by frequent stratigraphic gaps in many outcrops of Mesorif, Prerif areas and in the Bou Haddoud nappe. © 2011 Académie des sciences.
AUTHOR KEYWORDS: External Rif;  Lower Cretaceous;  Morocco;  Stratigraphy;  Submarine volcanism;  Upper Jurassic;  Volcaniclastic levels
DOCUMENT TYPE: Article
SOURCE: Scopus

Mele, D., Sulpizio, R., Dellino, P., la Volpe, L.
Stratigraphy and eruptive dynamics of a pulsating Plinian eruption of Somma-Vesuvius: The Pomici di Mercato (8900 years B.P.)
(2011) Bulletin of Volcanology, 73 (3), pp. 257-278. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955690114&partnerID=40&md5=65fef8003dc47dfe60b1b1864af1e231
AFFILIATIONS: CIRISIVU, c/o Dipartimento Geomineralogico, via Orabona 4, 70125 Bari, Italy
ABSTRACT: New volcanological studies allow reconstruction of the eruption dynamics of the Pomici di Mercato eruption (ca 8,900 cal. yr B. P.) of Somma-Vesuvius. Three main Eruptive Phases are distinguished based on two distinct erosion surfaces that interrupt stratigraphic continuity of the deposits, indicating that time breaks occurred during the eruption. Absence of reworked volcaniclastic deposits on top of the erosion surfaces suggests that quiescent periods between eruptive phases were short perhaps lasting only days to weeks. Each of the Eruptive Phases was characterised by deposition of alternating fall and pyroclastic density current (PDC) deposits. The fallout deposits blanketed a wide area toward the east, while the more restricted PDC deposits inundated the volcano slopes. Eruptive dynamics were driven by brittle magmatic fragmentation of a phonolitic magma, which, because of its mechanical fragility, produced a significant amount of fine ash. External water did not significantly contribute either to fragmentation dynamics or to mechanical energy release during the eruption. Column heights were between 18 and 22 km, corresponding to mass discharge rates between 1.4 and 6 × 107 kg s-1. The estimated on land volume of fall deposits ranges from a minimum of 2.3 km3 to a maximum of 7.4 km3. Calculation of physical parameters of the dilute pyroclastic density currents indicates speeds of a few tens of m s-1 and densities of a few kg m-3 (average of the lowermost 10 m of the currents), resulting in dynamic pressures lower than 3 kPa. These data suggest that the potential impact of pyroclastic density currents of the Pomici di Mercato eruption was smaller than those of other Plinian and sub-Plinian eruptions of Somma-Vesuvius, especially those of 1631 AD and 472 AD (4-14 kPa), which represent reference values for the Vesuvian emergency plan. The pulsating and long-lasting behaviour of the Pomici di Mercato eruption is unique in the history of large explosive eruptions of Somma-Vesuvius. We suggest an eruptive scheme in which discrete magma batches rose from the magma chamber through a network of fractures. The injection and rise of the different magma batches was controlled by the interplay between magma chamber overpressure and local stress. The intermittent discharge of magma during a large explosive eruption is unusual for Somma-Vesuvius, as well as for other volcanoes worldwide, and yields new insights for improving our knowledge of the dynamics of explosive eruptions. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Eruptive dynamics;  Plinian eruption;  Pomici di Mercato eruption;  Somma-Vesuvius
DOCUMENT TYPE: Article
SOURCE: Scopus

Furnes, H.a  b , de Wit, M.J.c , Robins, B.a , Sandstå, N.R.d 
Volcanic evolution of the upper Onverwacht Suite, Barberton Greenstone Belt, South Africa
(2011) Precambrian Research, 186 (1-4), pp. 28-50. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952624975&partnerID=40&md5=eef9b9bcbafc617886767e0404704dce
AFFILIATIONS: Department of Earth Science, University of Bergen, Allegt. 41, 5007 Bergen, Norway; 
Centre for Geobiology, University of Bergen, Allegt. 41, 5007 Bergen, Norway; 
AEON and Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa; 
Norwegian Petroleum Directorate, Post Box 600, 4003 Stavanger, Norway
ABSTRACT: The volcanic stratigraphy of the upper Onverwacht Suite in the southeastern part of the Paleoarchean Barberton Greenstone Belt has been investigated in 18 sections through parts of the Hooggenoeg, Kromberg, and lower Mendon Complexes. The ca. 2700. m thick volcanic sequence of the lowest tectonostratigraphic unit - the Hooggenoeg Complex (HC) - can be subdivided into 9 stratigraphic units representing major eruptive phases, each separated by silicified sedimentary and volcaniclastic rocks. The thicknesses of the units vary from <100. m to ∼700. m. Some units are wedge-shaped and die out over distances of a few kilometre along strike. The volcanic rocks are predominantly basaltic lavas, with minor basaltic komatiite and komatiite in the middle part of the HC. The basaltic lavas of the overlying tectonostratigraphic unit, the Kromberg Complex (KC), occur as screens within intrusives, or are in tectonic contact with adjacent rocks. The basal part (Ncakini section) of the tectonostratigraphically uppermost Mendon Complex (MC), consists of Mg-rich basalt lava. The lavas of the HC and KC are predominantly pillowed and massive flows, whereas those of the Ncakini section are exclusively massive. The massive and pillowed lava are commonly organized in cyclic units from 3. m to 32. m thick, and consisting of massive lava or large pillows that are succeeded by progressively smaller pillows. Cyclic units are inferred to have resulted from individual eruptions with decreasing rates of effusion. The pillow lavas of both the HC and KC contain <3-5% vesicles indicating eruption at greater depths than ∼2000. m. In general vesicular pillows occur in the lower part of both the HC and KC, and non-vesicular (and variolitic) lavas are found at the top, suggesting increasing water depths, and hence eruption in a subsiding basin. The chert layers within the HC include silicified tuffs derived from explosive subaerial or shallow-marine eruptions distant from the deep-water lavas of the HC and KC. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Barberton Greenstone Belt;  Tectonic setting;  Volcanic products - pillowed and massive lava;  Volcanic stratigraphy and architecture
DOCUMENT TYPE: Article
SOURCE: Scopus

Glen, R.A.a  b , Saeed, A.b , Quinn, C.D.a , Griffin, W.L.b 
U-Pb and Hf isotope data from zircons in the Macquarie Arc, Lachlan Orogen: Implications for arc evolution and Ordovician palaeogeography along part of the east Gondwana margin
(2011) Gondwana Research, 19 (3), pp. 670-685. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952068477&partnerID=40&md5=1527ce53d3a5950ef778fbc3afb12706
AFFILIATIONS: Geological Survey of New South Wales, Industry and Investment NSW, PO Box 344, Hunter Regional Mail Centre, NSW 2310, Australia; 
National Key Centre Geochemical Evolution and Metallogeny of Continents, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia
ABSTRACT: The Ordovician Macquarie Arc in the eastern subprovince of the Lachlan Orogen, southeastern Australia, is an unusual arc that evolved in four vertically stacked volcanic phases over ~37millionyears, and which is flanked by coeval, craton-derived, passive margin sedimentary terranes dominated by detrital quartz grains. Although these two terranes are marked by a general absence of provenance mixing, LA-ICPMS analysis of U-Pb and Lu-Hf contents in zircon grains in volcaniclastic rocks from 3 phases of the arc demonstrates the same age populations of detrital grains inherited from the Gondwana margin as those that characterise the flanking quartz-rich Ordovician turbidites. Magmatic Phase 1 is older, ~480Ma, and is characterised by detrital zircons grains with ages of ~490-540 with negative εHf from 0 to mainly -7.78, 550-625Ma ages with negative εHf from 0 to -26.6 and 970-1250Ma (Grenvillian) with εHf from +6.47 to -6.44. We have not as yet identified any magmatic zircons related to Phase 1 volcanism. Small amounts of detrital zircons also occur in Phase 2 (~468-455Ma), hiatus 1 and Phase 4 (~449-443Ma), all of which are dominated by Ordovician magmatic zircons with positive εHf values, indicating derivation from unevolved mantle-derived magmas, consistent with formation in an intraoceanic island arc. Because of the previously obtained positive whole rock εNd values from Phase 1 lavas, we rule out contamination from substrate or subducted sediments. Instead, we suggest that during Phase 1, the Macquarie Arc lay close enough to the Gondwana margin so that volcaniclastic rocks were heavily contaminated by detrital zircon grains shed from granites and Grenvillian mafic rocks mainly from Antarctica (Ross Orogen and East Antarctica) and/or the Delamerian margin of Australia. The reduced nature of a Gondwana population in Phase 2, hiatus 1 and Phase 4 is attributed to opening of a marginal basin between the Gondwana margin and the Macquarie Arc that put it out of reach of all but rare turbiditic currents. © 2010.
AUTHOR KEYWORDS: Australia;  Geochronology;  Gondwana margin;  Macquarie Arc;  Magmatism;  Zircon
DOCUMENT TYPE: Article
SOURCE: Scopus

García Massini, J.L., Jacobs, B.F.
The effects of volcanism on Oligocene-age plant communities from the Ethiopian Plateau, and implications for vegetational resilience in a heterogeneous landscape
(2011) Review of Palaeobotany and Palynology, 164 (3-4), pp. 211-222. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952696384&partnerID=40&md5=777f39a994a9f144cfeb8544be2860f5
AFFILIATIONS: Roy M. Huffington Department of Earth Sciences, Southern Methodist University, P O Box 750395, Dallas, TX 75275-0395, United States
ABSTRACT: Substantial volcanism and associated volcaniclastic sedimentation took place in association with East African Rift formation, and in some cases this would have had substantial ecological impacts. Ethiopian Late Oligocene (27.36 ± 0.11. Ma) fossiliferous volcanogenic strata provide opportunities to evaluate the magnitude of disruptive impact of volcanism on forest communities (before development of the Main Ethiopian Rift), and to assess their resilience. Fine-scale sampling and palynological analyses from the Magargaria River region of the northwestern Ethiopian Plateau tests the hypothesis that volcanism had a regional and significant disrupting effect on forest vegetation. These studies are compared with macrofossil and sedimentological data representing more local conditions previously reported from the same sediments. Results indicate that while some forests gave way to open environments dominated by herbaceous taxa, other communities remained or recovered quickly. Volcanic influences on sedimentary processes altered an existing forest ecosystem by creating a spatially heterogeneous landscape that also varied through time. This study supports the inherent significance of palynological data as indicators of ecological change at a regional scale relative to the more local view that macrofossils can provide, and underscores the importance of both kinds of fossils whenever possible for the study of the ecological dynamics of plant communities. The presence of forest taxa after repeated ashfalls indicates a degree of forest community resilience consistent with relatively limited burial by ash during the studied volcanic episodes. This study also suggests that taphonomic and diagenetic processes strongly affected the composition of palynomorph assemblages, skewing them towards thick-walled individuals, especially fungi. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Ethiopia;  Oligocene;  Paleoenvironmental reconstruction;  Palynology
DOCUMENT TYPE: Article
SOURCE: Scopus

Greenfield, J.E.a , Musgrave, R.J.a , Bruce, M.C.b , Gilmore, P.J.a , Mills, K.J.c 
The Mount Wright Arc: A Cambrian subduction system developed on the continental margin of East Gondwana, Koonenberry Belt, eastern Australia
(2011) Gondwana Research, 19 (3), pp. 650-669. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952073737&partnerID=40&md5=b8aa4d836dd8a1f2bf2cbfb8c3817644
AFFILIATIONS: Geological Survey of New South Wales, Industry and Investment NSW, PO Box 344, Hunter Region Mail Centre, NSW 2310, Australia; 
Geological Survey of New South Wales, Industry and Investment NSW, W.B. Clarke Geoscience Centre, 947-953 Londonderry Road, Londonderry NSW 2753, Australia; 
521 Williams Street, Broken Hill NSW 2880, Australia
ABSTRACT: The Mount Wright Arc, in the Koonenberry Belt in eastern Australia, is associated with two early to middle Cambrian lithostratigraphic groups developed onto the Late Neoproterozoic volcanic passive margin of East Gondwana. The Gnalta Group includes a calc-alkaline basalt-andesite-dacite suite (Mount Wright Volcanics), interpreted to represent the volcanic component of the arc. Volcaniclastic Gnalta Group rocks now buried in the Bancannia Trough represent the continental back-arc, developed immediately behind the arc in a manner analogous to the modern Taupo Volcanic Zone of New Zealand. East of the Gnalta Group is the Ponto Group, a deep marine sedimentary package that includes tholeiitic lavas (Bittles Tank Volcanics) and felsic tuffs, interpreted as part of a fore-arc sequence. The configuration of these units suggests the Mount Wright Arc developed on continental crust in response to west-dipping subduction along the East Gondwana margin, in contrast with some models for Cambrian convergence on other sections of the Delamerian Orogen, which invoke east-dipping subduction and arc accretion by arc-continent collision. This convergent margin was deformed by the middle Cambrian Delamerian Orogeny, which involved initial co-axial shortening followed by sinistral transpression, and oroclinal folding around the edge of the Curnamona Province. © 2010 International Association for Gondwana Research.
AUTHOR KEYWORDS: Delamerian Orogeny;  East Gondwana;  Koonenberry Belt;  Mount Wright Arc;  Tectonics
DOCUMENT TYPE: Article
SOURCE: Scopus

Haselwimmer, C.E.a  b  c , Riley, T.R.a , Liu, J.G.b 
Lithologic mapping in the Oscar II Coast area, Graham Land, Antarctic Peninsula using ASTER data
(2011) International Journal of Remote Sensing, 32 (7), pp. 2013-2035. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79953863427&partnerID=40&md5=822074ba43ae3717733ec9df6532c94b
AFFILIATIONS: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET, United Kingdom; 
Department of Earth Science and Engineering, South Kensington Campus, Imperial College London, SW7 2AZ, United Kingdom; 
Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, PO Box 757320, Fairbanks, AK 99775-7320, United States
ABSTRACT: The results of the first attempt to use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for the purposes of lithologic mapping on the Antarctic Peninsula are presented for an area on the Oscar II Coast, eastern Graham Land. This study included undertaking laboratory reflectance spectroscopy of ~70 rock samples from the study area and spectral lithologic analysis of two ASTER scenes. Spectra of the granitoids, silicic volcanic/volcaniclastic and terrestrial sedimentary rocks in the study area display a limited range of absorption features associated with muscovite, smectite and chlorite that are generally present as the alteration products of regional metamorphism. ASTER data analysis was undertaken using the reflective bands of the Level 1B registered radiance at-sensor data and the standard thermal infrared (TIR) emissivity product (AST05). For both wavelength regions, standard qualitative image processing methods were employed to define image end-members that were used as reference within Matched Filter (MF) processing procedures. The results were interpreted with reference to existing field observations, and photogeologic analysis of the ASTER visible to near-infrared (VNIR)/shortwave infrared (SWIR) data was used to resolve ambiguities in the spectral mapping results. The results have enabled the discrimination of most of the major lithologic groups within the study area as well as delineation of hydrothermal alteration zones of propylitic, and argillic grades associated with the Mesozoic Mapple Formation volcanics. The results have extended the mapped coverage of the Mapple Formation into un-investigated regions further north and validated previously inferred geological observations concerning other rocks throughout the study area. The outcomes will enable important revisions to be made to the existing geological map of the Oscar II Coast and demonstrate that ASTER data offers potential for improving geological mapping coverage across the Antarctic Peninsula. © 2011 Taylor & Francis.
DOCUMENT TYPE: Article
SOURCE: Scopus

de Wit, M.J.a , Furnes, H.b , Robins, B.c 
Geology and tectonostratigraphy of the Onverwacht Suite, Barberton Greenstone Belt, South Africa
(2011) Precambrian Research, 186 (1-4), pp. 1-27. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251600702&partnerID=40&md5=578beb9cdfdfd279bf54707d4f0c6491
AFFILIATIONS: AEON-Africa Earth Observatory Network and Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa; 
Department of Earth Science and Centre for Geobiology, University of Bergen, Allégt. 41, 5007 Bergen, Norway; 
Department of Earth Science, University of Bergen, Allégt. 41, 5007 Bergen, Norway
ABSTRACT: A synthesis of new and existing data reveals that at least seven major shear zones and an unconformity separate the rocks of the southern Barberton Greenstone Belt into seven units with different geological histories. Current views that these units constitute a continuous stratigraphic sequence and their subdivision into successive formations cannot be maintained. We argue here that the status of the traditional 'formations' of the Onverwacht Group of the Barberton Greenstone Belt be changed to 'complexes', and collectively these complexes be referred to as the Onverwacht Suite. The total age range and tectonostratigraphic thickness of the suite is about 120 million years and 15. km, respectively. The precise age range of the rocks present in each complex is largely unknown. The original spatial relationships between the complexes can in most cases only be inferred. All of the complexes include significant volumes of intrusions that were emplaced into the volcanic and volcaniclastic host rocks. The ages of the intrusions in the different complexes vary. In some complexes the intrusions and volcanic rocks have similar geochemistry and are probably co-magmatic. Others provide 'stitching' ages between complexes. Four of the complexes display internal relationships that resemble ophiolites. Basaltic pillowed and massive lavas are the most common rock types. Sheeted dykes are generally absent whilst multiple mafic sills are common and dominate one of the complexes. The volcanology and geochemistry of the complexes suggest that they formed predominantly in oceanic spreading and intra-oceanic arc environments at water depths of 1.7-4. km. The complexes were tectonically stacked during the final stages of their development, and during two subsequent orogenic events. One complex (the Hooggenoeg Complex) was uplifted and deeply eroded between about 3460 and 3470. Ma, with a minimum uplift rate (ca. 0.5. mm/yr) similar to that during emplacement of Phanerozoic ophiolites. Unconformably overlying, sub-aerial, coarse clastic sedimentary rocks (part of the newly distinguished Noisy Complex) overlap in age with felsic-intermediate igneous activity dated between 3445 and 3460. Ma that, in turn, is genetically related to tonalite-trondjemite plutons exposed farther to the south. The emergence of the deep water Hooggenoeg Complex above sea level, the start of its erosion and fluvial sedimentation on top of it at ca. 3458. Ma, represents the onset of its obduction onto older complexes, some of which are now preserved as enclaves in the granitoid terrains to the south. Other oceanic slabs (the Kromberg and the Mendon Complexes) were subsequently emplaced onto the Noisy Complex, during latitudinal displacements (ca. 12. cm/yr) that were not notably faster than today. Exhumation, with up to 18. km of unroofing along the southern margin of the greenstone belt, took place during a second orogenic episode of subduction and accretion between 3140 and 3230. Ma. This episode was associated with folding, thrusting and molasse-type sedimentation within the greenstone belt, coupled to extension and ductile faulting at a lower crustal level. During this period, younger complexes were assembled, and the older complexes re-cycled and eroded, at rates and with geotherms comparable to those in modern orogenic belts. In the Barberton region between 3.2 and 3.5. Ga tectonic processes appear to have operated at rates similar to those within modern evolving plate boundaries. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Barberton Greenstone Belt;  Cold paleoenvironments;  Onverwacht Suite;  Tectonostratigraphy;  Volcano-plutonic complexes
DOCUMENT TYPE: Article
SOURCE: Scopus

Fernandes, C.M.D.a , Juliani, C.b , Monteiro, L.V.S.c , Lagler, B.b , Echeverri Misas, C.M.b 
High-K calc-alkaline to A-type fissure-controlled volcano-plutonism of the São Félix do Xingu region, Amazonian craton, Brazil: Exclusively crustal sources or only mixed Nd model ages?
Journal of South American Earth Sciences, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952992709&partnerID=40&md5=3427158751339ccbbf46b3df2da7fb54
AFFILIATIONS: Faculdade de Geologia de Marabá, Universidade Federal do Pará, Folha 17 Quadra 04, Lote Especial, Nova Marabá, CEP 68505-080 begin_of_the_skype_highlighting              68505-080      end_of_the_skype_highlighting Marabá-PA, Brazil; 
Instituto de Geociências, Universidade de São Paulo, Rua do Lago 562, CEP 05508-080 São Paulo-SP, Brazil; 
Instituto de Geociências, Universidade Estadual de Campinas, Rua João Pandiá Calógeras, 51, Barão Geraldo, CEP 13083-970 Campinas-SP, Brazil
ABSTRACT: In the São Félix do Xingu region, southern portion of Amazonian craton, voluminous well-preserved Late Paleoproterozoic volcanic and plutonic rocks are grouped in the Sobreiro and Santa Rosa formations. The basal Sobreiro Formation (1.88 Ga) is composed of massive andesitic to rhyodacitic flows and volcaniclastic facies that are high-K and metaluminous, geochemically similar to calc-alkaline granitoids of volcanic arcs. Fractional crystallization of magnetite + augite + magnesiohastingsite (up to 20 vol. %) and zircon + plagioclase in most evolved rocks controlled the magmatic evolution of this unit, under oxidizing condition. The Santa Rosa Formation (1.87 Ga) comprises: 1) massive, bedded, and foliated rhyolitic lava flows, and large dikes of banded rhyolite and ignimbrite; 2) felsic ignimbrite associated with thin unwelded ash-fall tuff and highly rheomorphic felsic ignimbrite; 3) felsic crystal tuff, lapilli-tuff, and breccia; and 4) stocks and dikes of granitic porphyry, and subordinate equigranular granite intrusions. This unit was in part erupted along major fissures and has A-type intraplate geochemical affinity, peraluminous composition, and transitional subalkaline to alkaline characteristics. The magmatic evolution was predominantly controlled by fractional crystallization of zircon + apatite + Fe-Ti oxides + feldspars (up to 30 vol. %) with subordinate biotite, probably under intermediate oxidizing conditions. Nd model ages (3.0-2.49 Ga) for the Sobreiro Formation strongly suggest its generation by mixing of mantle-derived and anatectic melts of Archean rocks beneath the volcanic sequences in the São Félix do Xingu region. The Santa Rosa Formation could have been originated from several Archean crustal sources (TDM 3.12-2.56 Ga), involving assimilation/contribution of juvenile mantle components. The integrated data point to a narrow transition from Andean-type subduction to a dominantly extensional tectonic setting for the volcanic and plutonic event of the São Félix do Xingu region. A stage of flattening in the subduction angle of the subducted plate during the Paleoproterozoic ocean-continent orogenesis in the Tapajós Gold Province might explain the volcanism and plutonism in the São Felix do Xingu region as consequence of the arc migration, resulting in the ∼2.0-1.87 Ga geochronological and metallogenetic zoning observed in southern Amazonian craton. © 2011 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Carajás Mineral Province;  Flat subduction;  Nd isotope;  Paleoproterozoic;  Petrogenesis;  Plutonism;  Volcanism
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Saint-Ange, F.a  c , Savoye, B.b , Michon, L.c , Bachelery, P.c , Deplus, C.d , de Voogd, B.e , Dyment, J.d , le Drezen, E.b , Voisset, M.b , le Friant, A.d , Boudon, G.d 
A volcaniclastic deep-sea fan off La Réunion Island (Indian Ocean): Gradualism versus catastrophism
(2011) Geology, 39 (3), pp. 271-274. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951702797&partnerID=40&md5=9dc1287a678734131a9bac8350a1d487
AFFILIATIONS: Bedford Institute of Oceanography, Geological Survey of Canada (Atlantic), P.O. Box 1006, Dartmouth NS B2Y 4A2, Canada; 
Institut Français de Recherche pour l'Exploitation de la Mer, Laboratoire Environnements Sédimentaires, BP 70, 29280 Plouzané, France; 
Laboratoire GéoSciences Réunion, Université de La Réunion, Institut de Physique du Globe de Paris and Centre National de la Recherche Scientifique UMR7154, 15 av. René Cassin, BP 7151, 97715 St Denis messag, Réunion, France; 
Institut de Physique du Globe de Paris and Centre National de la Recherche Scientifique UMR 7154, 1 rue Jussieu, Paris, France; 
Modélisation et Imagerie en Géoscience-Pau, Centre National de la Recherche Scientifique UMR 5212, Université de Pau, 64000 Pau, France
ABSTRACT: A new geophysical data set off La Réunion Island (western Indian Ocean) reveals a large volcaniclastic submarine fan developing in an open-ocean setting. The fan is connected to a torrential river that floods during tropical cyclones. Sediment storage at the coast is limited, suggesting that the sediments are carried directly to the basin. The fan morphology and turbidites in cores lead us to classify it as a sand-rich system mainly fed by hyperpycnal flows. In the ancient geological record, there are many examples of thick volcaniclastic successions, but studies of modern analogues have emphasized mechanisms such as debris avalanches or direct pyroclastic flow into the sea. Because the Cilaos deep-sea fan is isolated from any continental source, it provides information on architecture and noncatastrophic processes in a volcaniclastic deep-sea fan. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Hayman, P.C., Cas, R.A.F.
Reconstruction of a multi-vent kimberlite eruption from deposit and host rock characteristics: Jericho kimberlite, Nunavut, Canada
(2011) Journal of Volcanology and Geothermal Research, 200 (3-4), pp. 201-222. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951724275&partnerID=40&md5=b2a33262f0f1fe787afd118ff095ccb4
AFFILIATIONS: School of Geosciences, Monash University, PO Box 28E, Victoria, 3800, Australia
ABSTRACT: The Jericho kimberlite (173.1. ±. 1.3. Ma) is a small (~. 130. ×. 70. m), multi-vent system that preserves products from deep (>. 1. km?) portions of kimberlite vents. Pit mapping, drill core examination, petrographic study, image analysis of olivine crystals (grain size distributions and shape studies), and compositional and mineralogical studies, are used to reconstruct processes from near-surface magma ascent to kimberlite emplacement and alteration. The Jericho kimberlite formed by multiple eruptions through an Archean granodiorite batholith that was overlain by mid-Devonian limestones ~. 1. km in thickness. Kimberlite magma ascended through granodiorite basement by dyke propagation but ascended through limestone, at least in part, by locally brecciating the host rocks. After the first explosive breakthrough to surface, vent deepening and widening occurred by the erosive forces of the waxing phase of the eruption, by gravitationally induced failures as portions of the vent margins slid into the vent and, in the deeper portions of the vent (>. 1. km), by scaling, as thin slabs burst from the walls into the vent. At currently exposed levels, coherent kimberlite (CK) dykes (<. 40. cm thick) are found to the north and south of the vent complex and represent the earliest preserved in-situ products of Jericho magmatism. Timing of CK emplacement on the eastern side of the vent complex is unclear; some thick CK (15-20. m) may have been emplaced after the central vent was formed. Explosive eruptive products are preserved in four partially overlapping vents that are roughly aligned along strike with the coherent kimberlite dyke. The volcaniclastic kimberlite (VK) facies are massive and poorly sorted, with matrix- to clast-supported textures. The VK facies fragmented by dry, volatile-driven processes and were emplaced by eruption column collapse back into the volcanic vents. The first explosive products, poorly preserved because of partial destruction by later eruptions, are found in the central-east vent and were formed by eruption column collapse after the vent was largely cleared of country rock debris. The next active vent was either the north or south vent. Collapse of the eruption column, linked to a vent widening episode, resulted in coeval avalanching of pipe margin walls into the north vent, forming interstratified lenses of country rock-rich boulder breccias in finer-grained volcaniclastic kimberlite. South vent kimberlite has similar characteristics to kimberlite of the north vent and likely formed by similar processes. The final eruptive phase formed olivine-rich and moderately sorted deposits of the central vent. Better sorting is attributed to recycling of kimberlite debris by multiple eruptions through the unconsolidated volcaniclastic pile and associated collapse events. Post-emplacement alteration varies in intensity, but in all cases, has overprinted the primary groundmass and matrix, in CK and VK, respectively. Erosion has since removed all limestone cover. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Grain size distributions;  Kimberlite reconstruction;  Magma fragmentation;  Olivine shape;  Vent growth
DOCUMENT TYPE: Article
SOURCE: Scopus

Carey, S.P.a , Camens, A.B.b , Cupper, M.L.c , Grün, R.d , Hellstrom, J.C.c , McKnight, S.W.a , Mclennan, I.a , Pickering, D.A.e , Trusler, P.f , Aubert, M.d 
A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains, Australia
(2011) Quaternary Science Reviews, 30 (5-6), pp. 591-610. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952041219&partnerID=40&md5=99ecd49ef63880c184c5acdb86495867
AFFILIATIONS: Centre for Environmental Management, School of Science and Engineering, University of Ballarat, PO Box 663, Ballarat, VIC 3353, Australia; 
Department of Earth and Environmental Sciences, University of Adelaide, South Australia 5005, Australia; 
School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia; 
Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia; 
Geoscience Unit, Museum Victoria, GPO Box 666, Melbourne, VIC 3001, Australia; 
School of Earth Sciences, Monash University, Clayton, VIC 3800, Australia
ABSTRACT: A diverse assemblage of late Pleistocene marsupial trackways on a lake bed in south-western Victoria provides the first information relating to the gaits and morphology of several megafaunal species, and represents the most speciose and best preserved megafaunal footprint site in Australia. The 60-110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid Diprotodon optatum, a macropodid (probably Protemnodon sp.) and a large vombatid (perhaps Ramsayia magna or '. Phascolomys' medius) and possible prints of the marsupial lion, Thylacoleo carnifex. The footprints were imprinted within a short time period, demonstrating the association of the taxa present, rather than the time-averaged accumulations usually observed in skeletal fossil deposits. Individual manus and pes prints are distinguishable in some trackways, and in many cases some digital pad morphology is also present. Several parameters traditionally used to differentiate ichnotaxa, including trackway gauge and the degree of print in-turning relative to the midline, are shown to be subject to significant intraspecific variation in marsupials. Sexual dimorphism in the trackway proportions of Diprotodon, and its potential for occurrence in all large bodied, quadrupedal marsupials, is identified here for the first time. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Diprotodontid;  Gait;  Ichnology;  Pleistocene;  Trackways;  Victoria
DOCUMENT TYPE: Article
SOURCE: Scopus

Jones, D.S.a , Barnes, C.G.b , Premo, W.R.c , Snoke, A.W.d 
The geochemistry and petrogenesis of the Paleoproterozoic Green Mountain arc: A composite(?), bimodal, oceanic, fringing arc
(2011) Precambrian Research, 185 (3-4), pp. 231-249. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951514253&partnerID=40&md5=117d9b4b1b5eba39ef31067ef950adcc
AFFILIATIONS: Department of Geosciences, Western Carolina University, Cullowhee, NC 28723, United States; 
Department of Geosciences, Texas Tech University, Lubbock, TX 79409, United States; 
U.S. Geological Survey, Denver Federal Center, MS 963, Box 25046, Denver, CO 80225, United States; 
Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, United States
ABSTRACT: The inferred subduction affinity of the ~1780-Ma Green Mountain arc, a dominantly bimodal igneous terrane (together with immature marine and volcaniclastic sedimentary rocks) accreted to the southern margin of the Wyoming province, is integral to arc-accretion models of the Paleoproterozoic growth of southern Laurentia. Conversely, the dominantly bimodal nature of many putative arc-related igneous suites throughout southern Laurentia, including the Green Mountain arc, has also been used to support models of growth by extension of pre-existing crust. We report new geochemical and isotopic data from ~1780-Ma gabbroic and granodioritic to tonalitic rocks of the Big Creek Gneiss, interpreted as consanguineous with previously studied metavolcanic rocks of the Green Mountain Formation.The ~1780-Ma Big Creek Gneiss mafic rocks show clear geochemical signatures of a subduction origin and provide no supporting evidence for extensional tectonism. The ~1780-Ma Big Creek Gneiss felsic rocks are attributed to partial melting of mafic and/or mixed lower-crustal material. The bimodal nature of the suite results from the combination of arc basalts and felsic crustal melts. The lack of andesite is consistent with the observed tholeiitic differentiation trend of the mafic magmas. The lower e{open}Nd(1780Ma) values for the felsic rocks vs. the mafic rocks suggest that the unexposed lower crust of the arc may be older than the arc and that Trans-Hudson- or Penokean-aged rocks possibly form the substratum of the arc. Our results reinforce previous interpretations that arc-related magmatism played a key role in the Paleoproterozoic crustal growth of southern Laurentia, but also support the possibility of unexposed older crust as basement to the arcs. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Big Creek Gneiss;  Crustal growth;  Geochemistry;  Green Mountain arc;  Proterozoic;  Yavapai
DOCUMENT TYPE: Article
SOURCE: Scopus

Berndt, J.a , Deutsch, A.b , Schulte, P.c , Mezger, K.a 
The Chicxulub ejecta deposit at Demerara Rise (western Atlantic): Dissecting the geochemical anomaly using laser ablation-mass spectrometry
(2011) Geology, 39 (3), pp. 279-282. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951695092&partnerID=40&md5=548491f9a091e763c53ad44a2901b30d
AFFILIATIONS: Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany; 
Institut für Planetologie, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany; 
GeoZentrum Nordbayern, Universität Erlangen, D-91054 Erlangen, Germany
ABSTRACT: We analyzed in situ the trace-element distributions in the pristine 2-cm-thick spherule-rich Cretaceous-Paleogene (K-Pg) event bed at Ocean Drilling Program (ODP) Leg 207 Site 1259C (Demerara Rise, western Atlantic) using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) with a spot diameter of 235 μm, corresponding to a sample volume of ~8.6 × 105 μm3. Unparalleled so far, this high resolution pinpoints the fallout of the Chicxulub projectile to the uppermost 2 mm of the K-Pg bed. Most of the Ni is not of extraterrestrial origin, as indicated by low, typical uppercrustal Ni/Cr ratios. Very low Zr/Hf and Nb/Ta ratios are confined exclusively to the K-Pg bed, indicating that storms and flooding spilled highly fractionated supracrustal material off the Guiana craton to reach the seafloor contemporaneously with the now-altered glass spherules. Chicxulub ejecta volumetrically dominate the K-Pg bed but contributed only minimally to the trace-element budget, as indicated by the very low rare earth element concentrations. At the top of the ejecta layer, together with the fallout of Pt from the impactor (~0.1 ppm), a pronounced Pb enrichment (up to 1500 ppm) occurs, which is interpreted to derive from the Guiana craton. Both elements obviously were contained in submicrometer-size particles that could only reach the seafloor attached to larger particles, the sedimentation of which may have occurred up to a year after the Chicxulub impact event. Our high-resolution analysis of the K-Pg event bed allows us, for the first time, to differentiate among the contributing components in detail, as well as assess the settling time frame of this geologically important boundary deposit. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Tani, K.a , Fiske, R.S.b , Dunkley, D.J.c , Ishizuka, O.a  d , Oikawa, T.d , Isobe, I.e , Tatsumi, Y.a 
The Izu Peninsula, Japan: Zircon geochronology reveals a record of intra-oceanic rear-arc magmatism in an accreted block of Izu-Bonin upper crust
(2011) Earth and Planetary Science Letters, 303 (3-4), pp. 225-239. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952101275&partnerID=40&md5=ff8d2c7981e71dc5c5a1ab619c84b5f2
AFFILIATIONS: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushimacho, Yokosuka, 237-0061, Japan; 
Smithsonian Institution MRC-119, Washington, DC 20013-7012, United States; 
National Institute of Polar Research, 10-3, Midoricho, Tachikawa, Tokyo, 190-8518, Japan; 
Institute of Geology and Geoinformation, Geological Survey of Japan/AIST, Central 7, 1-1-1, Higashi, Tsukuba, Ibaraki, 305-8567, Japan; 
Niijimamura Museum, 2-36-3, Honson, Niijima, Tokyo, 100-0402, Japan
ABSTRACT: The Izu Peninsula, central Japan, is situated in a zone where the active intra-oceanic Izu-Bonin arc has been colliding end-on with the mainland Honshu arc for the past 15. million years. As a result of this arc-arc collision, parts of the submarine Izu-Bonin upper crustal sequences have been accreted and uplifted to form the Izu Peninsula, exposing seafloor volcaniclastic deposits, associated lava flows, and coeval intrusive bodies. Parts of this sequence have been subjected to extensive hydrothermal alteration, and these altered rocks have previously been interpreted as representative of hypothetical widespread Middle Miocene basement that presumably underlay northern Izu-Bonin arc volcanoes. New zircon U-Pb ages presented here, however, show that both fresh and altered volcanic sequences exposed in Izu Peninsula are broadly contemporaneous and were products of the same Late Miocene to Pleistocene magmatism. Geochemical characteristics of these sequences show them to have formed in the Izu-Bonin rear-arc environment, providing an unusual opportunity to investigate in detail the growth and architecture of a rear-arc region in an active intra-oceanic arc. Moreover, zircon ages from altered basal units of Kozushima and Niijima, Quaternary volcanic islands in the northern Izu-Bonin rear-arc, show that these islands rest on units only slightly older (<. 1. Ma) than the main body of these subaerial edifices, not, as previously believed, part of a regional older Miocene basement. The near-continuum growth of these arc volcanoes and their underlying successions, plus the absence of a distinctly older basement underlying the Izu Peninsula and northern Izu-Bonin arc, provide new insight into upper crust development in an intra-oceanic, convergent margin environment. © 2011 Elsevier B.V.
AUTHOR KEYWORDS: Izu Peninsula;  Izu-Bonin arc;  Rear-arc;  Upper crust development;  Zircon U-Pb ages
DOCUMENT TYPE: Article
SOURCE: Scopus

Higgins, K., Hashimoto, T., Fraser, G., Rollet, N., Colwell, J.
Ion microprobe (SHRIMP) U-Pb dating of upper cretaceous volcanics from the northern Lord Howe Rise, Tasman Sea
(2011) Australian Journal of Earth Sciences, 58 (2), pp. 195-207. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951990248&partnerID=40&md5=1613e2bc9fba5d8835137c43ecd7d71e
AFFILIATIONS: Petroleum and Marine Division, Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia
ABSTRACT: Rock samples recovered during the Australian-French AUSFAIR MD153 Survey in 2006 from the northern Lord Howe Rise and the Fairway Ridge provide new constraints on the tectonostratigraphic evolution of the region and represent significant new information from a region in which few rocks have been dated. SHRIMP U-Pb dating of zircon from rocks from the Lord Howe Rise indicates alkali volcanism in the area at 97 Ma (trachyte) and 74 Ma (latite). The older volcanic activity is probably related to the widespread Late Cretaceous magmatism along the eastern Gondwana margin, whereas the younger activity may be related to the opening of the Tasman Sea or rifting in the New Caledonia Basin. The pebbly clasts and shell fossils in some of the associated volcaniclastic rocks provide evidence for the existence of landmasses as a sediment source area in the northern Lord Howe Rise region, and the initial marine incursion into the area around Campanian time. © 2011 Commonwealth of Australia (Geoscience Australia).
AUTHOR KEYWORDS: Cretaceous;  Eastern australia;  Fairway ridge;  Lord howe rise;  Shrimp;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Lowey, G.W.
Volcaniclastic gravity flow deposits in the Dezadeash Formation (Jura-Cretaceous), Yukon, Canada: Implications regarding the tectonomagmatic evolution of the Chitina arc in the northern Cordillera of North America
Lithos, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951581998&partnerID=40&md5=f2a245f00c0973af7f829cb288ac4d89
AFFILIATIONS: Yukon Geological Survey, Energy, Mines and Resources, Government of Yukon (K-10), 2099 2nd Ave., Whitehorse, Yukon, Canada Y1A 1B5
ABSTRACT: The Chitina arc in the northern Cordillera of North America evolved during the accretion of the Wrangellia composite terrane to the western margin of North America in the Jurassic and Cretaceous. The Dezadeash Formation, a 3000 m thick sequence of deepwater turbidites in southwestern Yukon, was deposited as a submarine fan in a backarc basin to the Chitina arc. Only limited geochemistry of altered volcanic rocks associated with the arc are available from southern Alaska. However, three thick volcaniclastic beds occur in the Dezadeash Formation. These consist of fine- to medium-grained vitric to crystal tuffs that are interpreted as resedimented syn-eruptive volcaniclastics. A U-Pb zircon age (149.4 ± 0.3 Ma) indicates they are contemporaneous with the Chitina arc. Petrographic examination shows the volcaniclastic rocks are altered mainly by albite and locally calcite, with a chemical index of alteration suggesting the rocks are relatively unweathered, or have undergone only incipient weathering. Harker diagrams indicate that CaO, K2O and Rb were mobile. Based on the Th vs. Co compositional diagram, the volcaniclastic rocks are classified as dacites, and according to various trace element plots they are calk-alkaline and adakite-like in composition. The volcaniclastic rocks plot in the active continental margin field on a variety of tectonic discriminant diagrams, and chondrite-normalized multi-element plots display parallel, listric-shaped profiles with significant light rare-earth element enrichment and minor heavy rare-earth element enrichment. Sm-Nd systematics indicate the volcaniclastic rocks represent mixing of a depleted mantle source and an older crustal source. These data suggest mainly slab dehydration with low pressure fractionation controlled by amphibole, with possibly minor input by slab melting. The Chitina arc has previously been interpreted as an oceanic island arc, and the continental arc signature of volcaniclastic rocks in the Dezadeash Formation, together with a continental arc signature of altered volcanic rocks in southern Alaska, is attributed to arc magmas erupting through Paleozoic volcanic, sedimentary and plutonic rocks of the Wrangellia composite terrane proxying for continental crust. © 2011 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Chitina arc;  Dezadeash formation;  Geochemistry;  Volcaniclastic
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Johnson, M.E.a , da Silva, C.M.b , Santos, A.c , Baarli, B.G.a , Cachão, M.b , Mayoral, E.J.c , Rebelo, A.C.b , Ledesma-Vázquez, J.d 
Rhodolith transport and immobilization on a volcanically active rocky shore: Middle Miocene at Cabeço das Laranjas on Ilhéu de Cima (Madeira Archipelago, Portugal)
(2011) Palaeogeography, Palaeoclimatology, Palaeoecology, 300 (1-4), pp. 113-127. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79551491699&partnerID=40&md5=a49a63474f11ee205df247cc3dfe991f
AFFILIATIONS: Department of Geosciences, Williams College, Williamstown, MA 01267, United States; 
Departamento de Geologia e Centro de Geologia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal; 
Departamento de Geodinámica y Paleontología, Facultad de Ciencias Experimentales, Universidad de Huelva, Campus de El Carmen, Avd. 3 de Marzo, s/n, 21071 Huelva, Spain; 
Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Ensenada, BC 22800, Mexico
ABSTRACT: Extraordinary deposits of fossil rhodoliths occur at the Cabeço das Laranjas (Portuguese~Hill of the Oranges) in a small fault block at the northwest end of Ilhéu de Cima off Porto Santo in the Madeira Archipelago. Stratigraphic repetitions of densely packed rhodolith beds up to 2.6m thick are associated with a receding rocky shoreline, and are interpreted as the result of hurricanes. The initial storm deposit sits unconformably on basalt and eroded basalt boulders associated with tuff and volcaniclastic breccia. Approximately 90,000 rhodoliths of Middle Miocene age (14-15Ma) are exposed on the upper surface of the initial deposit over a 450-m2 shelf exhumed from the hill's southeast side. Ranging in diameter from ≤3cm to 20cm, many of the rhodoliths generated by crustose coralline red algae are now iron stained and resemble a mass of oranges in gross appearance. Sea stacks and large boulders rise through the thick basal rhodolith bed to form small catchment areas that held the deposit in place after the storm's passage. The succeeding rhodolith deposits are variably separated by layers with mixed carbonate and volcanic sand, pure volcanic lapilli, and volcaniclastic tephra mixed with tuff showing swaley cross-stratification. Three out of four rhodolith beds are truncated against the flank of the adjoining rocky shore. Only the youngest (fourth) rhodolith layer is fully exposed around the perimeter of the hill and can be shown to cross a basalt barrier that is traceable for 70m in cross section as an erosional ramp dipping from 6° to 8° southeast. The entire fossil-rich sequence is capped by a basalt flow showing columnar disjunction. Based on thin-section analysis, three genera of coralline red algae are recognized in the basal rhodolith deposit: Sporolithon, Lithothamnion, and Neogoniolithon. Associated biodiversity is low, represented by 16 kinds of marine invertebrates dominated by encrustations and borings on the rhodoliths and very few free body fossils. The Madeira region of the North Atlantic may have been susceptible to major cyclonic storms immediately after the Middle Miocene Climate Optimum, when a northward shift of the Inter-tropical Convergence Zone was stimulated by a steeper temperature gradient in the southern hemisphere related to expansion of continental glaciers on Antarctica. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Coastal paleotopography;  Madeira Archipelago;  Middle Miocene Climate Optimum (MMCO);  Obrution deposits;  Rhodoliths;  Serravallian Stage;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Gallego, O.F.a , Cabaleri, N.G.b , Armella, C.b , Volkheimer, W.c , Ballent, S.C.d , Martínez, S.e , Monferran, M.D.a , Silva Nieto, D.G.f , Páez, M.A.g 
Paleontology, sedimentology and paleoenvironment of a new fossiliferous locality of the Jurassic Cañadón Asfalto Formation, Chubut Province, Argentina
(2011) Journal of South American Earth Sciences, 31 (1), pp. 54-68. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651498954&partnerID=40&md5=eb36ec9ad604ac535f08973b796b5743
AFFILIATIONS: Centro de Ecología Aplicada del Litoral, Consejo Nacional de Investigaciones Científicas y Técnicas, C.C.128, C.P. 3400 Corrientes, Argentina; 
Instituto de Geocronología y Geología Isotópica, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Ciudad Universitaria, C1428EHA Buenos Aires, Argentina; 
Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Centro Científico - Tecnológico, Consejo Nacional de Investigaciones Científicas y Técnicas, C.C. 330, 5500 Mendoza, Argentina; 
División Paleontologia Invertebrados, Facultad de Ciencias Naturales y Museo, Pasaje Teruggi s/n, Paseo del Bosque, La Plata 1900, Argentina; 
Dpto. Evolución de Cuencas, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay; 
Servicio Geológico Minero Argentino, Instituto de Geología y Recursos Minerales, Av. Julio A. Roca 651, 10 Piso, C1067ABB Buenos Aires, Argentina; 
Comisión Nacional de Energía Atómica, Regional Patagonia, C.C. 178, Parque Industrial, 9100 Trelew, Chubut, Argentina
ABSTRACT: A new Late Jurassic assemblage of " conchostracans", ostracods, bivalves and caddisfly cases from the locality " Estancia La Sin Rumbo", Chubut Province (Patagonia, Argentina) is recorded. The fossils occur in the upper part of an outcropping 45 m thick volcaniclastic lacustrine sequence of yellowish tuffs and tuffites of the Puesto Almada Member, which is the upper member of the Cañadón Asfalto Formation with U/Pb age of 161 ± 3. Ma. The sequence represents one sedimentary cycle composed of a (lower) hemicycle of expansion and a (higher) hemicycle of contraction of the water body. The invertebrates lived in small freshwater bodies during the periods of expansion of the lake. The occurrence of a great number of small spinicaudatans, associated with mud-cracks, is evidence of dry climatic conditions and suggests several local mortality events. The spinicaudatan record of the fushunograptid-orthestheriid (component of the Eosestheriopsis dianzhongensis fauna) and the presence of Congestheriella rauhuti Gallego and Shen, suggest a Late Jurassic (Oxfordian to Tithonian) age. Caddisfly cases are recorded for the first time in the Cañadón Asfalto Basin. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Argentina;  Cañadón Asfalto Formation;  Late Jurassic;  Paleontology;  Patagonia;  Sedimentology
DOCUMENT TYPE: Article
SOURCE: Scopus

Caballero, L.a , Capra, L.b 
Textural analysis of particles from El Zaguán debris avalanche deposit, Nevado de Toluca volcano, Mexico: Evidence of flow behavior during emplacement
(2011) Journal of Volcanology and Geothermal Research, 200 (1-2), pp. 75-82. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78751573958&partnerID=40&md5=5090479f9af5d27c6c4afc4a68d37ae5
AFFILIATIONS: Posgrado en Ciencias de la Tierra, Instituto de Geología, UNAM, Ciudad Universitaria, 04510, México City, Mexico; 
Centro de Geociencias, UNAM, Campus Juriquilla, 76230 Qro., Mexico
ABSTRACT: El Zaguán deposit originated at 28,000. yrs.B.P. from the flank collapse of Nevado de Toluca, a dacitic stratovolcano of the Transmexican Volcanic Belt. Scanning Electron Microprobe analyses (SEM) were performed on some particles from this deposit to observe microtextures produced during transport and emplacement of the debris avalanche flow. Particles from 2Φ (250 μm), 0Φ (1. mm) and-2Φ (4. mm) granulometric classes were randomly selected at different outcrops, and their surface textures were described. The observed textures are divided in two groups, Basal and Upper textures, each one indicating different clast interactions. Basal textures are observed predominantly in the lower part of the deposit and consist of parallel ridges, parallel grooves, scratches and lips. Upper textures are mainly present in the upper part of the deposit and consisted of fractures, percussion marks, and broken or grinded crystals. These characteristics, coupled with field observations such as the presence of clastic dikes and deformed lacustrine mega-blocks, indicate that the basal part of the debris avalanche was moving in a partially liquefied state. By contrast, the particles in the upper part were able to move freely, interacting by collision. These microscopic textures are in agreement with previously described emplacement behaviors in debris avalanches of volcanic origin, suggesting a stratified flow dominated by different transport and depositional mechanisms depending upon flow depth and possible fluid content at their base. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Debris avalanche;  Flow emplacement;  Nevado de Toluca;  SEM;  Texture
DOCUMENT TYPE: Article
SOURCE: Scopus

Genna, D.a  b , Gaboury, D.a  b  c , Moore, L.a , Mueller, W.U.a 
Use of micro-XRF chemical analysis for mapping volcanogenic massive sulfide related hydrothermal alteration: Application to the subaqueous felsic dome-flow complex of the Cap d'Ours section, Glenwood rhyolite, Rouyn-Noranda, Québec, Canada
(2011) Journal of Geochemical Exploration, 108 (2), pp. 131-142. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951849671&partnerID=40&md5=db7dc0ace6d968139e459031328e9911
AFFILIATIONS: Centre d'études en ressources minérales (CERM), Université du Québec à Chicoutimi (UQAC), 555, boul. de l'Université, Chicoutimi, QC, Canada; 
Laboratoire de métallogénie expérimentale et quantitative (LAMEQ), Université du Québec à Chicoutimi (UQAC), 555, boul. de l'Université, Chicoutimi, QC, Canada; 
Consortium de recherche en exploration minérale (CONSOREM), Université du Québec à Chicoutimi (UQAC), 555, boul. de l'Université, Chicoutimi, QC, Canada
ABSTRACT: A new analytical method using micro-X-ray fluorescence (XRF) is presented for the in situ analysis of major elements in rock samples. This approach has allowed for a separate study of hydrothermal alteration of matrix versus fragments in volcaniclastic material (i.e. flow breccia). This is particularly important for volcanogenic massive sulfide (VMS) exploration in subaqueous felsic dome-flow complexes, where brecciated facies are omnipresent and the imprint of hydrothermal alteration is typically heterogeneous. In this study, eleven elements are measured with a 1.7 by 1.3. mm window considered to be representative of each sample, based on replicate analyses. An average is calculated for the analyzed window and yields a nearly complete analysis with the exception of loss of ignition (LOI). Micro-XRF data were validated using whole rock XRF analyses performed on the same sample block. The application of this chemical method has been tested successfully on thin sections from the Cap d'Ours section of the Glenwood rhyolite in the Rouyn-Noranda region of Québec, Canada. With 58 samples spaced at approximately 50 m intervals, two styles of alteration zoning were recognized: (1) a lateral and concordant zoning expressed by vent-proximal silicification in the west grading toward vent-distal chlorite-sericite alteration to the east, and (2) vertical and discordant zoning expressed by stronger sericitization in the upper part of later volcanic quartz- and feldspar-phyric endogenous lobes. The former is typical of cooling induced by seawater interaction at the lava-water interface at temperatures greater than 400. °C, whereas the latter is related to lower temperature (<300. °C) hydrothermal mineralization associated with endogenous lobe emplacement within the volcanic pile. The presented results clearly demonstrate the potential use of the micro-XRF data for characterizing weak to intense hydrothermal alteration in highly fragmented volcanic rocks. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Abitibi belt;  Dome-flow complex;  Hydrothermal alteration mapping;  Micro-XRF chemical analysis;  New-Senator caldera;  Volcanogenic massive sulfide exploration
DOCUMENT TYPE: Article
SOURCE: Scopus

Henderson, R.A.a , Innes, B.M.b , Fergusson, C.L.c , Crawford, A.J.d , Withnall, I.W.e 
Collisional accretion of a Late Ordovician oceanic island arc, northern Tasman Orogenic Zone, Australia
(2011) Australian Journal of Earth Sciences, 58 (1), pp. 1-19. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78951492460&partnerID=40&md5=3556122aeccae7bc48c68fe4b79c127c
AFFILIATIONS: School of Earth and Environmental Sciences, James Cook University, Townsville Qld 2811, Australia; 
Newmont Asia Pacific, Level 1, 388 Hay Street, Subiaco WA 6008, Australia; 
School of Earth and Environmental Science, University of Wollongong, Wollongong NSW 2522, Australia; 
CODES ARC Centre of Excellence, University of Tasmania, Private Bag 126, Hobart, TAS 7001, Australia; 
Geological Survey of Queensland, 80 Meiers Road, Indooroopilly, QLD 4068, Australia
ABSTRACT: A distinctive Late Ordovician volcano-sedimentary terrane, embracing the Carriers Well Formation and Everetts Creek Volcanics and dismembered slivers now structurally intercalated in the adjoining Wairuna Formation, is located within the Broken River Province of the northern Tasmanides. It abuts a basement of mafic-ultramafic rocks (Gray Creek Complex) and overlying Early Ordovician deep marine sedimentary and volcanic strata (Judea Formation) which host tonalitic plutons. The terrane lies at the western, inboard-margin of the Camel Creek Subprovince, a broad tract of multiply deformed mid-Paleozoic turbidites with minor basalt and chert variously interpreted as the infill of a backarc basin or an accretionary wedge. U-Pb dates from detrital zircon indicate a maximum Late Silurian age for siliciclastic rocks from the previously undated Wairuna Formation. Geochemistry of volcanic rocks from the volcano-sedimentary terrane show them to be largely of mafic to intermediate compositions of calc-alkaline affinity, comparable with broadly coeval Macquarie Arc volcanic suites of the southern Tasmanides. Trace-element systematics identify a subduction relationship for the volcanic suite and V/Ti employed as a discrimination tool identifies the terrane as representing an oceanic island arc, consistent with its sedimentary facies which include volcaniclastic mass flow deposits, limestone, and radiolarian chert. Continent-derived sandstone in the sedimentary assemblage, confirmed by the ages of detrital zircon from a sandstone sample from the Carriers Well Formation, indicates that the oceanic island arc developed proximal to the Late Ordovician continental margin of East Gondwana. Its nature and location bear on the tectonic setting of the entire Camel Creek Subprovince, for which interpretation as an Early Silurian-Early Devonian accretionary wedge is favoured. Collision of the island arc with the continental margin, and associated deformation of part the intervening oceanic crustal tract, now represented by the Gray Creek Complex and its sedimentary cover (Judea Formation) registers the initiation of subduction accretion in late Early Silurian (Llandoverian) time. It marks earlystage orogenesis in the Broken River Province, accurately timed by stratigraphic relationships in the basinal succession developed in the Graveyard Creek Subprovince immediately to the west of the arc assemblage. Tectonism was regionally developed in north Queensland at this time, coeval with the Benambran Orogeny of the Lachlan Orogen in which the Macquarie Arc was likewise accreted to the East Gondwana margin. Benambran orogenesis marks a general phase of shortening, and removal by subduction, of oceanic crust and inversion of continent-derived overlying sedimentary cover along the East Gondwana margin. © 2011 Geological Society of Australia.
AUTHOR KEYWORDS: Benambran Orogeny;  Broken River Province;  Collisional accretion;  East Gondwana;  Oceanic island arc;  Ordovician;  Tasman Orogenic Zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Ebrahimi, S.a , Alirezaei, S.b , Pan, Y.c 
Geological setting, alteration, and fluid inclusion characteristics of Zaglic and Safikhanloo epithermal gold prospects, NW Iran
(2011) Geological Society Special Publication, (350), pp. 133-147. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651518423&partnerID=40&md5=d22d42143595b3cfd70974bb1423172a
AFFILIATIONS: School of Mining, Petroleum and Geophysics Engineering, Shahrood University, Shahrood, Iran; 
Faculty of Earth Sciences, University of Shahid Beheshti, Tehran, Iran; 
Department of Geological Sciences, University of Saskatchewan, Saskatoon, S7N 5E2, Canada
ABSTRACT: The Zaglic and Safikhanloo epithermal gold prospects are located in the Arasbaran zone, to the west of the Cenozoic Alborz-Azarbaijan magmatic belt in NW Iran. Mineralization is mainly restricted to quartz and quartz -carbonate veins and veinlets. Pyrite is the main sulphide, associated with subordinate chalcopyrite and bornite. Gold occurs as microscopic and submicroscopic grains in quartz and pyrite. The country rocks are Tertiary intermediate-mafic volcanic and volcaniclastic rocks of andesite to trachy-andesite composition intruded by a composite granitic to syenitic pluton. They are medium to high-K, calc-alkaline and alkaline rocks and display fractionated REE (rare earth element) patterns, with light rare earth elements (LREE) significantly enriched relative to the heavy rare elements (HREE). On primitive mantle normalized plots, they display depletions in Nb, Ti and P, and enrichments in Pb, which are common characteristics of arc-related magmas worldwide. Hydrothermal alteration minerals developed in the wall rocks include quartz, calcite, pyrite, kaolinite, montmorillonite, illite, chlorite, and epidote. Minor alunite occurs in Safikhanloo. Gold is locally enriched in the altered rocks immediate to the veins. The ore-stage quartz from both prospects is dominated by liquid-rich fluid inclusions; vapourrich inclusions are rare. The homogenization temperature varies between 170-230 and 170-330 °C and salinity varies between 1.4 to 9.5 and,1 to 6.7 wt% NaCl equivalent, for Safikhanloo and Zaglic, respectively. The occurrence of hydrothermal breccias, bladed calcite, adularia, and rare coexisting vapour and liquid-dominant inclusions suggest that boiling occurred in the course of the evolution of the ore fluids. The large variations in Th and the salinity values can be explained by boiling and/or mixing. Lack of sulphate minerals in the veins suggests that sulphides and gold precipitated from a reduced, H2S-dominant fluid. Calculated δ34S values for the ore fluid vary between 24.6 and 29.3‰. Sulphur could have been derived directly from magmatic sources, or leached from the volcanic and plutonic country rocks. Ore formation in Zaglic and Safikhanloo occurred in response to mixing, boiling, and interactions with wall rocks. Considering the intermediate-argillic alteration, the low contents of base metal sulphides, and the overall low salinities, the Zaglic and Safikhanloo can be classified as low-sulphidation epithermal systems. © 2011 Geological Society of London.
DOCUMENT TYPE: Article
SOURCE: Scopus

Utsunomiya, A.a , Jahn, B.-M.a , Okamoto, K.b , Ota, T.c , Shinjoe, H.d 
Intra-oceanic island arc origin for Iratsu eclogites of the Sanbagawa belt, central Shikoku, southwest Japan
(2011) Chemical Geology, 280 (1-2), pp. 97-114. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650750104&partnerID=40&md5=7e31d0871ac34497c8977a6360f4118a
AFFILIATIONS: Institute of Earth Sciences, Academia Sinica, Academia Road 2-128, Nankang, Taipei 11529, Taiwan; 
Faculty of Education, Saitama University, Saitama 338-8570, Japan; 
Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-0193, Japan; 
Faculty of Business Administration, Tokyo Keizai University, Tokyo 185-8502, Japan
ABSTRACT: New geochemical and Sr-Nd isotopic data for the Iratsu eclogite and surrounding metamorphic rocks of the Sanbagawa belt, Japan, show that, while the protoliths of the metamorphic rocks formed in a variety of tectonic settings, the Iratsu body represents a deeply subducted and accreted island arc. The igneous protoliths of eclogites and garnet amphibolites were probably generated from a mantle source that had components of both a depleted mantle modified by slab-released fluid (as seen in a negative Nb anomaly) and an enriched mantle, similar to that of ocean island basalts (OIB). Fractional crystallization modeling indicates that the protoliths of some garnet clinopyroxenites from the Iratsu body are cumulates from a basaltic magma that crystallized under high O2 and H2O fugacities in the middle to lower crust. The source characteristics and crystallization conditions suggest that the protoliths of the Iratsu rocks formed in an oceanic island arc. Quartz eclogites from the marginal zone of the Iratsu body have geochemical signatures similar to turbidites from the Izu-Bonin island arc (as seen in a negative Nb anomaly and a concave REE pattern). The protoliths might be volcaniclastic turbidites that formed in a setting proximal to the oceanic island arc. Geochemical and isotopic signatures of the surrounding mafic schists are similar to normal (N-) and enriched (E-) mid-ocean-ridge basalt (MORB), and distinct from the rocks from the Iratsu body. The protoliths of the mafic schists likely formed in a plume-influenced mid-ocean ridge or back-arc basin. Pelitic schists from the surrounding rocks and pelitic gneisses from the marginal zone of the Iratsu body have evolved, continental geochemical signatures (as seen in a negative εNd(t) value (~-5)), consistent with their origin as continent-derived trench-fill turbidites. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Eclogites;  Isotopic geochemistry;  Oceanic island arc;  Sanbagawa belt
DOCUMENT TYPE: Article
SOURCE: Scopus

Robertson, A.H.F.a , Ustaömer, T.b 
Role of tectonic-sedimentary melange and Permian-Triassic cover units, central southern Turkey in Tethyan continental margin evolution
(2011) Journal of Asian Earth Sciences, 40 (1), pp. 98-120. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78449306667&partnerID=40&md5=8812ef81b960402f0290d49ef3342693
AFFILIATIONS: School of GeoSciences, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, United Kingdom; 
Department of Geology, Istanbul University, 34850 Avcidotlesslar, Istanbul, Turkey
ABSTRACT: Melanges play a key role in the interpretation of orogenic belts, including those that have experienced deformation and metamorphism during continental collision. This is exemplified by a Palaeozoic tectonic-sedimentary melange (part of the Konya complex) that is exposed beneath a regionally metamorphosed carbonate platform near the city of Konya in central Anatolia. The Konya complex as a whole comprises three units: a dismembered, latest Silurian-Early Carboniferous carbonate platform, a Carboniferous melange made up of sedimentary and igneous blocks in a sedimentary matrix (also known as the Hali{dotless}ci{dotless} Group or Si{dotless}zma Group), and an overlying Volcanic-sedimentary Unit (earliest Permian?). The Palaeozoic carbonates accumulated on a subsiding carbonate platform that bordered the northern margin of Gondwana, perhaps as an off-margin unit. The matrix of the melange was mainly deposited as turbidites, debris flows and background terrigenous muds. Petrographic evidence shows that the clastic sediments were mostly derived from granitic and psammitic/pelitic metamorphic rocks, typical of upper continental crust. Both extension- and contraction-related origins of the melange can be considered. However, we interpret the melange as a Carboniferous subduction complex that formed along the northern margin of Gondwana, related to partial closure of Palaeotethys. Blocks and slices of Upper Palaeozoic radiolarian chert, basic igneous rocks and shallow-water carbonates were accreted and locally reworked by gravity processes. Large (up to km-sized) blocks and slices of shallow-water limestone were emplaced in response to collision of the Palaeozoic Carbonate Platform with the subduction zone. The overlying Volcanic-sedimentary Unit (earliest Permian?) comprises alkaline lava flows, interbedded with volcaniclastic debris flows and turbidites, volcanogenic shales and tuff. The complex as a whole is overlain by shallow-water, mixed carbonate-siliciclastic sediments of mainly Late Permian age that accumulated on a regional-scale shelf adjacent to Gondwana. Successions pass transitionally into Lower Triassic rift-related shallow-water carbonates and terrigenous sandstones in the southwest of the area. In contrast, Triassic sediments in the southeast overlie the melange unconformably and pass upwards from non-marine clastic sediments into shallow-marine calcareous sediments of Mid-Triassic age, marking the base of a regional Mesozoic carbonate platform. During the latest Cretaceous-Early Cenozoic the entire assemblage subducted northwards and underwent high pressure/low temperature metamorphism and polyphase folding as a part of the regional Anatolide unit. © 2010.
AUTHOR KEYWORDS: Carboniferous;  Melange;  Palaeotethys;  Southern Turkey;  Subduction
DOCUMENT TYPE: Article
SOURCE: Scopus

Tonarini, S.a , Leeman, W.P.b , Leat, P.T.c 
Subduction erosion of forearc mantle wedge implicated in the genesis of the South Sandwich Island (SSI) arc: Evidence from boron isotope systematics
(2011) Earth and Planetary Science Letters, 301 (1-2), pp. 275-284. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650287409&partnerID=40&md5=75c534dd2c567ad4f7e010722ded9292
AFFILIATIONS: Istituto Geoscienze e Georisorse, CNR, Via Moruzzi1, 56124 Pisa, Italy; 
National Science Foundation, Arlington, VA 22230, United States; 
British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom
ABSTRACT: The South Sandwich volcanic arc is sited on a young oceanic crust, erupts low-K tholeiitic rocks, is characterized by unexotic pelagic and volcanogenic sediments on the down-going slab, and simple tectonic setting, and is ideal for assessing element transport through subduction zones. As a means of quantifying processes attending transfer of subduction-related fluids from the slab to the mantle wedge, boron concentrations and isotopic compositions were determined for representative lavas from along the arc. The samples show variable fluid-mobile/fluid-immobile element ratios and high enrichments of B/Nb (2.7 to 55) and B/Zr (0.12 to 0.57), similar to those observed in western Pacific arcs. δ11B values are among the highest so far reported for mantle-derived lavas; these are highest in the central part of the arc (+15 to +18%) and decrease toward the southern and northern ends (+12 to +14%) δ11B is roughly positively correlated with B concentrations and with 87Sr/86Sr ratios, but poorly coupled with other fluid-mobile elements such as Rb, Ba, Sr and U. Peridotites dredged from the forearc trench also have high δ11B (ca. +10%) and elevated B contents (38-140ppm). Incoming pelagic sediments sampled at ODP Site 701 display a wide range in δ11B (+5 to -13%; average=-4.1%), with negative values most common. The unusually high δ11B values inferred for the South Sandwich mantle wedge cannot easily be attributed to direct incorporation of subducting slab materials or fluids derived directly therefrom. Rather, the heavy B isotopic signature of the magma sources is more plausibly explained by ingress of fluids derived from subduction erosion of altered frontal arc mantle wedge materials similar to those in the Marianas forearc. We propose that multi-stage recycling of high-δ11B and high-B serpentinite (possibly embellished by arc crust and volcaniclastic sediments) can produce extremely 11B-rich fluids at slab depths beneath the volcanic arc. Infiltration of such fluids into the mantle wedge likely accounts for the unusual magma sources inferred for this arc. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Boron isotopes;  Subduction zones;  Volcanic arc magmatism
DOCUMENT TYPE: Article
SOURCE: Scopus

Carey, S.N.a , Schneider, J.-L.b 
Volcaniclastic processes and deposits in the deep-sea
(2011) Developments in Sedimentology, 63 (C), pp. 457-515. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650154900&partnerID=40&md5=9fefa680968472f660332bb9c8aa340c
AFFILIATIONS: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, United States; 
Université Bordeaux 1, Observatoire Aquitain des Sciences de l'Univers, CNRS-UMR EPOC, Talence Cedex, France
ABSTRACT: Volcanic activity at ocean-spreading centers, large oceanic islands, and especially subduction zones, leads to several types of eruptive and non-eruptive processes that generate large volumes of volcaniclastic sediments, and results in the deposition of fragmental material in the deep-sea. Volcaniclastic material forms an important part of sedimentary successions, particularly along active margins of both cordilleran and islandarc environments, and around large volcanic oceanic islands. This chapter presents an overview of the large diversity of volcaniclastic processes and deposits that can be recognized in deep-marine environments (i.e. beyond the shelf/slope break). The various aspects of their origin, recognition, and interpretation will be emphasized from the individual depositional interval to the volcaniclastic apron scale. © 2011 Heiko Hüneke and Thierry Mulder.
DOCUMENT TYPE: Book
SOURCE: Scopus

Chetel, L.M.a , Janecke, S.U.b , Carroll, A.R.a , Beard, B.L.a , Johnson, C.M.a , Singer, B.S.a 
Paleogeographic reconstruction of the Eocene Idaho River, North American Cordillera
(2011) Bulletin of the Geological Society of America, 123 (1-2), pp. 71-88. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251490083&partnerID=40&md5=6cd728fb01ab020de7a5e9e3da6c21f6
AFFILIATIONS: Department of Geoscience, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, United States; 
Department of Geology, Utah State University, Logan, UT 84322, United States
ABSTRACT: Eocene Lake Gosiute in southwestern Wyoming was progressively filled in by volcaniclastic sediment between 49.6 and 47.0 Ma. The source of this material has long been thought to have been the Absaroka volcanic province, immediately north of the greater Green River Basin. Lead isotope compositions of sandstone from this interval, however, are consistent with derivation from the Challis volcanic field. The 40Ar/39Ar ages of single detrital K-feldspar crystals from greater Green River Basin sandstones are nearly identical to 40Ar/39Ar eruptive ages for volcanic rocks of the Challis volcanic field (49.8-45.5 Ma), but we also identify Mesozoic and Proterozoic crystals that are consistent with cooling ages for rocks that were likely exposed in the Idaho segment of the North American Cordillera during the Eocene. Most of these rocks are traversed by or are up-gradient of a major Eocene paleovalley in central Idaho. The sudden appearance of Challis-derived sediment in the greater Green River Basin indicates that a major river, here named the Idaho River, connected the interior of the North American Cordillera to the greater Green River Basin. This connection requires 500 km to reach from central Idaho to the greater Green River Basin. The Idaho River probably carried detritus that was stripped from distant uplifted mountains above the active Challis volcanic field as far south as the Piceance Creek Basin, suggesting a total length of at least 1000 km. Middle Eocene metamorphic core complexes in the northern Cordillera likely produced a major highland in the headwaters of the Idaho River, which generated river systems that drained both eastward into the Wyoming foreland and westward into the Oregon Coast ranges. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Pierson, T.C.a , Pringle, P.T.b , Cameron, K.A.c 
Magnitude and timing of downstream channel aggradation and degradation in response to a dome-building eruption at Mount Hood, Oregon
(2011) Bulletin of the Geological Society of America, 123 (1-2), pp. 3-20. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251518263&partnerID=40&md5=c1f4ad773169fa57e44da57ca2aabc7d
AFFILIATIONS: U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, WA 98683, United States; 
Science Department, Centralia College, Centralia, WA 98531, United States; 
Oregon Department of Environmental Quality, Portland, OR 97204, United States
ABSTRACT: A dome-building eruption at Mount Hood, Oregon, starting in A.D. 1781 and lasting until ca. 1793, produced dome-collapse lithic pyroclastic fl ows that triggered lahars and intermittently fed 108 m3 of coarse volcaniclastic sediment to sediment reservoirs in headwater canyons of the Sandy River. Mobilization of dominantly sandy sediment from these reservoirs by lahars and seasonal fl oods initiated downstream migration of a sediment wave that resulted in a profound cycle of aggradation and degradation in the lowermost reach of the river (depositional reach), 61-87 km from the source. Stratigraphic and sedimentologic relations in the alluvial fill, together with dendrochronologic dating of degradation terraces, demonstrate that (1) channel aggradation in response to sediment loading in the headwater canyons raised the river bed in this reach at least 23 m in a decade or less; (2) the transition from aggradation to degradation in the upper part of this reach roughly coincided with the end of the dome-building eruption; (3) fluvial sediment transport and deposition, augmented by one lahar, achieved a minimum average aggradation rate of ~2 m/yr; (4) the degradation phase of the cycle was more prolonged than the aggradation phase, requiring more than half a century for the river to reach its present bed elevation; and (5) the present longitudinal profile of the Sandy River in this reach is at least 3 m above the pre-eruption profile. The pattern and rate of channel response and recovery in the Sandy River following heavy sediment loading resemble those of other rivers similarly subjected to very large sediment inputs. The magnitude of channel aggradation in the lower Sandy River, greater than that achieved at other volcanoes following much larger eruptions, was likely enhanced by lateral confinement of the channel within a narrow incised valley. A combination of at least one lahar and winter floods from frequent moderate-magnitude rainstorms and infrequent very large storms was responsible for flushing large volumes of sediment to the depositional reach. These conditions permitted a sedimentation response in the Sandy River that approached the magnitude of channel aggradation resulting elsewhere from large explosive eruptions and high-intensity rainfall regimes, despite the fact that the Sandy River aggradation was in response to an unremarkable dome-building eruption in a climate dominated by low to moderate rainfall intensities. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

De Kock, G.S.a , Armstrong, R.A.b , Siegfried, H.P.a , Thomas, E.c 
Geochronology of the Birim Supergroup of the West African craton in the Wa-Bolé region of west-central Ghana: Implications for the stratigraphic framework
(2011) Journal of African Earth Sciences, 59 (1), pp. 1-40. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78449306209&partnerID=40&md5=a0e93837abc1382f531b1959d783d3ce
AFFILIATIONS: Council for Geoscience, Private Bag X112, Pretoria 0001, South Africa; 
Research School of Earth Sciences, The Australian National University, Mills Road, Canberra 0200, Australia; 
36, rue des Palombes, 65290 Louey, France
ABSTRACT: The Birim rocks of the West African craton comprise belts of greenschist- to amphibolite-grade gneiss and schist, and subparallel basins of greenschist-grade phyllite of volcaniclastic and epiclastic origin, which were intruded by igneous rocks. The granitoids intruded between 2213 and 2060. Ma and overlap with the volcaniclastic units dated between 2211 and 2064. Ma. The simultaneous occurrence of the magmatic events and irregular distribution of the rock ages hamper the formulation of a stratigraphic succession. SHRIMP spot analyses were done on older cores, crystals and rims from 23 rocks from the Bolé-Wa region in west-central Ghana. The crystallization ages range from 2195 to 2118. Ma, the inherited ages from 2876 to 2130. Ma, and metamorphic ages from 2114 to 2090. Ma. Aided by metamorphic, structural and chemical studies an older geotectonic cycle (2195-2150. Ma), containing the Dole and Guropie Suite and Bolé Group, was established. These units were subjected to several orthogonal and shear deformation events. These events were followed by the contemporaneous Sawla calc-alkaline monzonitic plutonism (2132-2126. Ma) and deposition of the epiclastic Maluwe Group (2137-2125. Ma) of calc-alkaline felsic to tholeiitic volcanic origin. Deformation of the basin beds was succeeded by the intrusion of the Tanina Suite granitoids of 2122-2120. Ma, which, themselves, were deformed prior to 2119. Ma. At 2118. Ma syenite and gabbro intruded along conjugate extension fractures. The gabbro and syenite of the Wakawaka Suite were only affected by three events of brittle strike-slip faulting. The first had significant displacement along NNE- to NE-directed shear zones, while the latter only formed conjugate joint systems with limited transport. Palaeo- to Neoarchaean cores, the oldest yet reported in the Baoulé Mossi domain, are restricted to the gneissic Dole Suite biotite granites. The presence of Dole-, Guropie-, Sawla-, and Tanina-aged older cores and grains in younger rocks reflects continuous reworking of the developing crust during successive magmatic episodes. Zircon rim growth between 2105 and 2090. Ma indicates posttectonic crustal thickening. The low Rb/Sr Ro of ∼0.7032 of gabbro and monzonite, and the recycling of the Birim-age crust confirm the primary and juvenile nature of the West African craton after ∼2195. Ma. With the various ages obtained, it was possible to link deposition, magmatism and deformation to crustal processes, and establish the cyclic geotectonic evolution in the West Africa craton (individual basin opening and closure) over time as part of an intraoceanic arc-back-arc basin system. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Geochronology;  Geotectonic evolution;  Ghana;  Stratigraphy;  West African craton
DOCUMENT TYPE: Review
SOURCE: Scopus

Biass, S., Bonadonna, C.
A quantitative uncertainty assessment of eruptive parameters derived from tephra deposits: The example of two large eruptions of Cotopaxi volcano, Ecuador
(2011) Bulletin of Volcanology, 73 (1), pp. 73-90. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651240446&partnerID=40&md5=9216112f159dbf8488e0c9dc6bf35347
AFFILIATIONS: Département de Minéralogie, Université de Genève, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland
ABSTRACT: Physical parameters of explosive eruptions are typically derived from tephra deposits. However, the characterization of a given eruption relies strongly on the quality of the dataset used, the strategy chosen to obtain and process field data and the particular model considered to derive eruptive parameters. As a result, eruptive parameters are typically affected by a certain level of uncertainty and should not be considered as absolute values. Unfortunately, such uncertainty is difficult to assess because it depends on several factors and propagates from field sampling to the application and interpretation of dispersal models. Characterization of explosive eruptions is made even more difficult when tephra deposits are poorly exposed and only medial data are available. In this paper, we present a quantitative assessment of the uncertainty associated with the characterization of tephra deposits generated by the two largest eruptions of the last 2,000 years of Cotopaxi volcano, Ecuador. In particular, we have investigated the effects of the determination of the maximum clast on the compilation of isopleth maps, and, therefore, on the characterization of plume height. We have also compared the results obtained from the application of different models for the determination of both plume height and erupted volume and for the eruption classification. Finally, we have investigated the uncertainty propagation into the calculation of mass eruption rate and eruption duration. We have found that for our case study, the determination of plume height from isopleth maps is more sensitive to the averaging techniques used to define the maximum clast than to the choice of dispersal models used (i. e. models of Carey and Sparks 1986; Pyle 1989) and that even the application of the same dispersal model can result in plume height discrepancies if different isopleth lines are used (i. e. model of Carey and Sparks 1986). However, the uncertainties associated with the determination of erupted mass, and, as a result, of the eruption duration, are larger than the uncertainties associated with the determination of plume height. Mass eruption rate is also associated with larger uncertainties than the determination of plume height because it is related to the fourth power of plume height. Eruption classification is also affected by data processing. In particular, uncertainties associated with the compilation of isopleth maps affect the eruption classification proposed by Pyle (1989), whereas the VEI classification is affected by the uncertainties resulting from the determination of erupted mass. Finally, we have found that analytical and empirical models should be used together for a more reliable characterization of explosive eruptions. In fact, explosive eruptions would be characterized better by a range of parameters instead of absolute values for erupted mass, plume height, mass eruption rate and eruption duration. A standardization of field sampling would also reduce the uncertainties associated with eruption characterization. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Cotopaxi;  Eruptive parameters;  Mass eruption rate;  Maximum clast;  Plume height;  Tephra;  Volume
DOCUMENT TYPE: Article
SOURCE: Scopus

Smellie, J.L.a  c , Rocchi, S.b , Armienti, P.b 
Late Miocene volcanic sequences in northern Victoria Land, Antarctica: Products of glaciovolcanic eruptions under different thermal regimes
(2011) Bulletin of Volcanology, 73 (1), pp. 1-25. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651230163&partnerID=40&md5=c79d8a311191cc76ab6f0e467b711b40
AFFILIATIONS: British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom; 
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy; 
Department of Geology, University of Leicester, University Road, Leicester LS1 7RH, United Kingdom
ABSTRACT: Late Miocene (c. 13-5 Ma) volcanic sequences of the Hallett Volcanic Province (HVP) crop out along >250 km of western Ross Sea coast in northern Victoria Land. Eight primary volcanic and six sedimentary lithofacies have been identified, and they are organised into at least five different sequence architectures as a consequence of different combinations of eruptive and/or depositional conditions. The volcanoes were erupted in association with a Miocene glacial cover and the sequences are overwhelmingly glaciovolcanic. The commonest and most representative are products of mafic aa lava-fed deltas, a type of glaciovolcanic sequence that has not been described before. It is distinguished by (1) a subaerially emplaced relatively thin caprock of aa lavas lying on and passing down-dip into (2) a thicker association of chaotic to crudely bedded hyaloclastite breccias, water-chilled lava sheets and irregular lava masses, collectively called lobe-hyaloclastite. A second distinctive sequence type present is characterised by water-cooled lavas and associated sedimentary lithofacies (diamictite (probably glacigenic) and fluvial sands and gravels) similar to some mafic glaciovolcanic sheet-like sequences (see Smellie, Earth-Science Reviews, 74, 241-268, 2008), but including (for the first time) examples of likely sheet-like sequences with felsic compositions. Other sequence types in the HVP are minor and include tuff cones, cinder cones and a single ice-marginal lacustrine sequence. The glacial thermal regime varied from polar, characterised by sequences lacking glacial erosion, glacigenic sediments or evidence for free water, to temperate or sub-polar for sequences in which all of these features are conspicuously developed. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: aa lava-fed deltas;  Felsic sheet-like sequences;  Glacial thermal regime;  Glaciovolcanism;  Lithofacies;  Miocene;  Sequence architecture
DOCUMENT TYPE: Article
SOURCE: Scopus

Ordonez-Calderon, J.C.a  b , Polat, A.a  c , Fryer, B.J.a  c , Gagnon, J.E.a  c 
Field and geochemical characteristics of Mesoarchean to Neoarchean volcanic rocks in the Storø greenstone belt, SW Greenland: Evidence for accretion of intra-oceanic volcanic arcs
(2011) Precambrian Research, 184 (1-4), pp. 24-42. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650232962&partnerID=40&md5=0ee14a94817f12b723e2f3897b137e22
AFFILIATIONS: Department of Earth and Environmental Sciences, University of Windsor, Windsor, ON N9B 3P4, Canada; 
Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada; 
Great Lakes Institute for Environmental Research, University of Windsor, Windsor, ON N9B 3P4, Canada
ABSTRACT: The Storø greenstone belt, southern West Greenland, consists of thrust-imbricated slices of Mesoarchean (&gt;3060Ma) and Neoarchean (ca. 2800Ma) mafic to ultramafic volcanic rocks, volcaniclastic sediments, and gabbro-anorthosite associations. The belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600Ma. The contacts between the Mesoarchean and Neoarchean volcanic rocks, and surrounding Eoarchean to Neoarchean tonalite-trondhjemite-granodiorite (TTG) gneisses are tectonic and typically bounded by high-grade mylonites. Regardless of age, the volcanic rocks are dominated by mafic amphibolites with a tholeiitic basalt composition, near-flat to slightly enriched light rare earth element (LREE) patterns (La/Smcn=0.91-1.48), relatively flat to slightly depleted heavy-REE (HREE) (Gd/Ybcn=1.0-1.28), and pronounced negative Nb-Ta anomalies (Nb/Nb*=0.34-0.73) on chondrite- and primitive mantle-normalized diagrams. These geochemical characteristics are consistent with subduction zone geochemical signatures and partial melting of a shallow (&lt;80km) mantle source free of residual garnet. There is no geochemical evidence for contamination by older continental crust. The overall field and geochemical characteristics suggest that the thrust-imbricated basaltic rocks were erupted in intra-oceanic subduction zone settings. Sedimentary rocks are represented by garnet-biotite and quartzitic gneisses. They are characterized by relatively high contents of transition metal (Ni=10-154ppm; Cr=7-166ppm) and enriched LREE patterns (La/Smcn=1.38-3.79). These geochemical characteristics suggest that the sedimentary rocks were derived from erosion of felsic to mafic igneous source rocks. Collectively, the structural and lithogeochemical characteristics of the Storø greenstone belt are consistent with collision (accretion) of unrelated Archean volcanic rocks formed in supra-subduction zone geodynamic settings. Accordingly, the Mesoarchean and Neoarchean rock record of the Storø greenstone belt may well be explained in terms of modern-style plate tectonic processes. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Amphibolites;  Archean;  Greenstone belt;  Island arc tholeiites;  Supra-subduction zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Lander, E.B.a , Lindsay, E.H.b 
Merychyus calaminthus (Mammalia, Artiodactyla, Oreodontidae) of probable early late Arikareean (late Oligocene to late early Miocene) age from the lower part of the Chalk Canyon Formation, Maricopa and Yavapai counties, central Arizona
(2011) Journal of Vertebrate Paleontology, 31 (1), pp. 215-226. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79951559098&partnerID=40&md5=4886544325f78957e93430ba887fb69e
AFFILIATIONS: Paleo Environmental Associates, Inc., 2248 Winrock Ave., Altadena, CA 91001-3205, United States; 
University of Arizona, Department of Geosciences, Tucson, AZ 85721-0077, United States
ABSTRACT: Late Oligocene and early Miocene, nearly flat-lying and dominantly volcaniclastic, continental strata in the lower part of the Chalk Canyon Formation are exposed in central Arizona along the southwestern margin of the Transition Zone and the adjacent northeastern margin of the Basin and Range Province. The strata have yielded both of the two known oreodont records reported from Arizona. These occurrences represent the Cave Creek and Black Canyon Local Faunas. Both records are assigned tentatively to the early late Arikareean (Ar3), small-bodied oreodontid species Merychyus calaminthus, based primarily on their occlusal and basicranial anatomies and on the comparatively small sizes of the individuals they represent. Both fossil sites are in discontinuous exposures separated by about 28 km (17 mi). Overlying olivine-rich basaltic lava flows still in the lower part of the formation in the Cave Creek area are as old as 23.3 ± 2.7 Ma in age, based on whole-rock Potassium-Argon radiometric age determinations. On the other hand, a pumice-rich air-fall tuff bed at the base of the formation is only 20.98 ± 0.06 and 21.03 ± 0.06 Ma old, based on 40Argon/39Argon (Ar/Ar) analysis. A blue ash layer in the Black Canyon City area and at the approximate level of the oreodont site is 23.7 ± 0.9 Ma old, based on the 238Uranium-206Lead analysis of zircon crystals. The oreodont records and nearly all available radiometric data suggest that the fossil-bearing strata in the lower part of the Chalk Canyon Formation are correlatives of the Harrison Formation in the northwestern Nebraska Panhandle. The Agate Ash in the Harrison Formation is 23.23 ± 0.13 Ma in age on the basis of Ar/Ar analysis. © 2011 by the Society of Vertebrate Paleontology.
DOCUMENT TYPE: Article
SOURCE: Scopus

Santana, M.M.U.a , Moura, M.A.b , Olivo, G.R.c , Botelho, N.F.b , Kyser, T.K.c , Bühn, B.b 
The La Unión Au ± Cu prospect, Camagüey District, Cuba: Fluid inclusion and stable isotope evidence for ore-forming processes
(2011) Mineralium Deposita, 46 (1), pp. 91-104. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251636444&partnerID=40&md5=28e9a80b72ee7cdceb7f5980488c115f
AFFILIATIONS: Instituto de Geología y Paleontología, Vía Blanca s/n, San Miguel del Padrón, La Habana, Cuba; 
Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, Asa Norte, 70910-900 Brasília, DF, Brazil; 
Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON K7l3N6, Canada
ABSTRACT: The Camagüey district, Cuba, is known for its epithermal precious metal deposits in a Cretaceous volcanic arc setting. Recently, the La Unión prospect was discovered in the southern part of the district, containing gold and minor copper mineralization interpreted as porphyry type. Mineralization is hosted in a 73.0 ± 1.5 Ma calc-alkaline I-type oxidized porphyry quartz diorite intrusive within volcanic and volcaniclastic rocks of the early Cretaceous Guáimaro Formation. The porphyry is affected by propylitic alteration and crosscut by a network of quartz and carbonate veinlets and veins. Chlorite, epidote, sericite, quartz, and pyrite are the main minerals in the early veins which are cut by late carbonate and zeolite veins. Late barite pseudomorphously replaces pyrite. Gold is associated with pyrite as disseminations in the altered quartz diorite and in the veins, occurring as inclusions or filling fractures in pyrite with 4 g/t Au in bulk samples, and up to 900 ppm Au in in pyrite. Fluid inclusion and oxygen isotope data are consistent with a H2O-NaCl-(KCl) mineralizing fluid, derived from the quartz diorite magma, and trapped at least at 425°C and 1.2 kbar. This primary fluid unmixed into two fluid phases, a hypersaline aqueous fluid and a low-salinity vapor-rich fluid. Boiling during cooling may have played an important role in metal precipitation. Pyrite δ34S values for the La Unión prospect range between 0.71‰ and 1.31‰, consistent with a homogeneous magmatic sulfur source. The fluids in equilibrium with the mineralized rocks have estimated δ18O values from 8‰ to 11.8‰, calculated for a temperature range of 480-505°C. The tectonic environment of the La Unión prospect, its high gold and low copper contents, the physical-chemical characteristics of the mineralizing fluids and the isotopic signature of the alteration minerals and fluids indicate that the La Unión gold mineralization is similar to the porphyry gold type, even though the ore-related epidote-chlorite alteration can be classified as propylitic and not the classic potassic and/or phyllic alteration. The low copper contents in the prospect could be due to a mineralizing fluid previously saturated in copper, which is indicated by trapped chalcopyrite crystals in high-temperature fluid inclusions. The low-temperature paragenesis, represented by carbonate, zeolite and barite, indicates epithermal overprint. The study shows the potential for other gold porphyry-type deposits in the Cretaceous volcanoplutonic arc of Cuba. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Camagüey;  Cuba;  Fluid inclusions;  Porphyry gold-copper;  Stable isotopes
DOCUMENT TYPE: Article
SOURCE: Scopus

Maxeiner, R.O.a , Rayner, N.b 
Continental arc magmatism along the southeast Hearne Craton margin in Saskatchewan, Canada: Comparison of the 1.92-1.91Ga Porter Bay Complex and the 1.86-1.85Ga Wathaman Batholith
(2011) Precambrian Research, 184 (1-4), pp. 93-120. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650246820&partnerID=40&md5=1fc0c9e917ad862232a82f6304f190a8
AFFILIATIONS: Saskatchewan Geological Survey, 200 - 2101 Scarth St., Regina, SK S4P 2H9, Canada; 
Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada
ABSTRACT: Detailed mapping, coupled with geochronological and geochemical investigations, has revealed the presence of a 1917-1913. Ma gabbro-monzodiorite-monzonite suite along the southeast margin of the Hearne Craton in northern Saskatchewan, Canada. The predominantly plutonic suite is also characterised by 1915. Ma old trachyandesitic subvolcanic and volcaniclastic inclusions. The rocks are hornblende-epidote-titanite. ± augite bearing and collectively termed the Porter Bay Complex. The plutonic rocks cut the 2569. Ma Lueaza River granitoid suite, a component of the Hearne Craton and are themselves intruded by 1859. Ma pegmatitic diorite, 1856. Ma layered gabbro-anorthosite, and 1853. Ma quartz-diorite belonging to the Wathaman Batholith, one of the world's largest Paleoproterozoic Andean-type continental arcs. Wholerock major element geochemistry characterises the Porter Bay Complex as calc-alkalic to alkali-calcic, metaluminous and variable from ferroan to magnesian. Trace element concentrations are characterised by negative high field strength element anomalies, suggesting emplacement along a destructive plate margin. The geochemical signatures of the Wathaman Batholith and the Porter Bay Complex are largely identical. The geographic location, map relationships, and geochronological, geochemical and petrographic constraints are consistent with the Porter Bay Complex having formed in a subduction-related continental arc setting. The southeastern margin of the Hearne Craton was therefore a long-lived active continental margin with two separate periods of continental arc magmatism between 1.92-1.91. Ga and 1.86-1.85. Ga. © 2010.
AUTHOR KEYWORDS: Geochemistry;  Geochronology;  Neoarchean;  Paleoproterozoic;  Peter Lake Domain;  Porter Bay Complex;  Trans-Hudson Orogen;  Wathaman Batholith
DOCUMENT TYPE: Article
SOURCE: Scopus

Hansen, J.a , Jerram, D.A.a , McCaffrey, K.a , Passey, S.R.b 
Early Cenozoic saucer-shaped sills of the Faroe Islands: An example of intrusive styles in basaltic lava piles
(2011) Journal of the Geological Society, 168 (1), pp. 159-178. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651507926&partnerID=40&md5=47500b06f3a8499bd9e2a3c0b4bc6fba
AFFILIATIONS: Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom; 
Jardfeingi (Faroese Earth and Energy Directorate), Brekkutún 1, P.O. Box 3059, FO-110, Tórshavn, Faroe Islands
ABSTRACT: The Early Cenozoic igneous activity of the North Atlantic Igneous Province that generated widespread sill complexes in sedimentary basins at the NW European margins also generated various intrusive systems in the contemporaneous basaltic lava pile of the Faroe Islands. The Faroe Island Basalt Group comprises seven formations with a total thickness of about 6.5 km, of which four major formations are built up of tholeiitic lava flows, each being several hundred metres thick, and three thinner formations are mostly built up of volcaniclastic lithologies, each being a few metres to a few tens of metres thick. The largest sills are exposed as partly saucer-shaped bodies in the three uppermost formations, where inner gently dipping basal sill sections gradually give way to more steeply inclined discordant outer rims that commonly cut several hundred metres into overlying lava flows. Numerous subvertical and moderately inclined dykes ranging in thickness from c. 0.5 to c. 4.0 m intersect the areas affected by sill intrusion, but only inclined dykes or sheets have been positively identified as sill feeders. Locally controlled rotations of least principal stress axes σ3 during initial sill intrusion or propagation may have been an important contributing factor in determining the overall geometry of the investigated intrusions. © 2011 Geological Society of London.
DOCUMENT TYPE: Article
SOURCE: Scopus

Ballato, P.a , Uba, C.E.a , Landgraf, A.a , Strecker, M.R.a , Sudo, M.a , Stockli, D.F.b , Friedrich, A.c , Tabatabaei, S.H.d 
Arabia-Eurasia continental collision: Insights from late Tertiary foreland-basin evolution in the Alborz Mountains, Northern Iran
(2011) Bulletin of the Geological Society of America, 123 (1-2), pp. 106-131. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251522507&partnerID=40&md5=dd2d3beb6561dd252bbce8e52ccc81d6
AFFILIATIONS: Institut für Erd- und Umweltwissenschaften, DFG Leibniz Center for Surface Process and Climate Studies, Universität Potsdam, Karl-Liebknecht-Strasse 24, 14476 Potsdam, Germany; 
Department of Geology, University of Kansas, 1475 Jayhawk Blvd.,, Lawrence, KS 66044, United States; 
Department für Geo und Umweltwissenschaften, Ludwig-Maximilians Universität München, Luisen-Strasse 37, 80333 München, Germany; 
Building and Housing Research Center, Sheikh Fazlollah Exp. Way, Tehran 13145-1696, Iran
ABSTRACT: A poorly understood lag time of 15-20 m.y. exists between the initial Arabia-Eurasia continental collision in late Eocene to early Oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late Miocene. The late Eocene to Miocene-Pliocene clastic and shallow-marine sedimentary rocks of the Kond, Eyvanekey, and Semnan Basins in the Alborz Mountains (northern Iran) offer the possibility to track the evolution of this orogen in the framework of collision processes. A transition from volcaniclastic submarine deposits to shallow-marine evaporites and terrestrial sediments occurred shortly after 36 Ma in association with reversals in sediment provenance, strata tilting, and erosional unroofing. These events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched Arabian lithosphere. This early stage of collision produced topographic relief associated with shallow foreland basins, suggesting that shortening and tectonic loading occurred at low rates. Starting from the early Miocene (17.5 Ma), fl exural subsidence in response to foreland basin initiation occurred. Fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early Miocene. We suggest that the lag time between the initiation of continental collision (36 Ma) and the acceleration of regional deformation (20-17.5 Ma) reflects a two-stage collision process, involving the "soft" collision of stretched lithosphere at first and "hard" collision following the arrival of unstretched Arabian continental litho sphere in the subduction zone. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Bickford, M.E.a , Basu, A.b , Patranabis-Deb, S.c , Dhang, P.C.c , Schieber, J.b 
Depositional history of the Chhattisgarh Basin, Central India: Constraints from new SHRIMP zircon ages
(2011) Journal of Geology, 119 (1), pp. 33-50. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651263547&partnerID=40&md5=e9f1b0110d34492581be6d8abf0b9556
AFFILIATIONS: Department of Earth Sciences, Syracuse University, Syracuse, NY 13244, United States; 
Department of Geological Sciences, Indiana University, Bloomington, IN 47405, United States; 
Indian Statistical Institute, 203 B. T. Road, Kolkata, 700108, India
ABSTRACT: The Indian Shield includes the Singhbhum, Bastar, and East and West Dharwar cratons. Proterozoic sedimentary basins formed on these cratons have preserved rocks with a range of degrees of metamorphism and deformation. In the Chhattisgarh Basin, within the Bastar Craton, the ca. 2200-2500-m-thick Chhattisgarh Supergroup has been preserved in nearly pristine condition. Previous work has shown that the Sukhda Tuff, located about 2200 m from the base of the section, was formed ca. 1007 Ma. New U-Pb SHRIMP age determinations show that the Singhora Tuff, located about 100 m above the base of the basin, is not older than 1405 ± 9 Ma. Thus, most of the Chhattisgarh Supergroup was deposited between 1400 and 1000 Ma. Age data for detrital zircons from sandstones show that, regardless of their stratigraphic position, there is a unimodal age peak near 2500 Ma, the typical age of adjacent granitic and rhyolitic basement rocks, indicating that these constituted the principal provenance of the sediments in the Chhattisgarh Basin. However, near the top of the succession, the Sarnadih Sandstone and a volcaniclastic sandstone near Sukhda Village, show a wide range of ages with peaks from ca. 1000 through 2680 Ma. The ca. 1000-Ma detrital zircons were probably derived from igneous sources similar to the Sukhda Tuff, but the zircons with other ages indicate a different source. Age data from rock units in the Central Indian Tectonic Zone to the north of the basin match this age spectrum better than any to the south of the basin and are consistent with a change in provenance direction to a northerly source late in the basin-filling cycle.
DOCUMENT TYPE: Article
SOURCE: Scopus

Wainwright, A.J.a , Tosdal, R.M.a , Forster, C.N.b , Kirwin, D.J.c , Lewis, P.D.d  f , Wooden, J.L.e  g 
Devonian and carboniferous arcs of the oyu tolgoi porphyry Cu-Au district, South Gobi region, Mongolia
(2011) Bulletin of the Geological Society of America, 123 (1-2), pp. 306-328. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251488161&partnerID=40&md5=e4dc27329508721071f1fcb55019a7c6
AFFILIATIONS: Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada; 
4011 Pipeline Road, Blaine, WA 98230, United States; 
Ivanhoe Mines, 51/278 Muang Ake, Tambon lak 6, Amphoe Muang, Pathumtani, Bangkok 12000, Thailand; 
15715 Mountainview Drive, Surrey, BC V3S 0C6, Canada; 
U.S. Geological Survey, MS-901, Menlo Park, CA 94025, United States; 
El Dorado Gold, 1188-550 Burrard Street, Vancouver, BC V6C 2B5, Canada; 
Department of Geological and Environmental Science, Stanford University, Stanford, CA 94304, United States
ABSTRACT: The Central Asian orogenic belt consists of microcontinental blocks and mobile belts positioned between the Siberian craton and the Tarim and North China cratons. Extending across Asia for 5000 km, the belt consists of terranes that decrease in age southward away from the Siberian craton. A time-stratigraphic-structural sequence for the rocks is critical to defining the tectonic evolution of the belt. In the Oyu Tolgoi area of the South Gobi Desert (Mongolia), Devonian and Carboniferous rocks record the construction of multiple arcs, formation of a giant porphyry Cu-Au system, exhumation, and polyphase deformation. The oldest rocks are basaltic volcanic and subvolcanic rocks of the Devonian Alagbayan Group intruded by Late Devonian quartz monzodiorite stocks and dikes, which host giant porphyry Cu-Au deposits. The rocks were exhumed, overlain by pyroclastic rocks, and then tectonically buried by marine mafic supracrustal rocks prior to the youngest Devonian granodiorite intrusions. The postmineral Carboniferous Gurvankharaat Group unconformably overlying the deformed terrane consists of effusive, pyroclastic, subvolcanic and volcaniclastic rocks, as well as sedimentary units. The supracrustal rocks underwent polyphase shortening after 330 Ma and prior to 290 Ma. Variations in stratigraphic sequences suggest that the region is underlain by a submarine arc that became emergent during the Upper Devonian and remained subaerial to shallow subaqueous through much of the Carboniferous. Xenocrystic zircons in igneous rocks suggest that the offshore arcs were sufficiently close to ancient crust to have interacted with detritus shed into marine basins, most likely from the Siberian craton and fringing early Paleozoic terranes. © 2011 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Calvari, S.a , Tanner, L.H.b 
The Miocene Costa Giardini diatreme, Iblean Mountains, southern Italy: model for maar-diatreme formation on a submerged carbonate platform
(2010) Bulletin of Volcanology, pp. 1-20. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650622131&partnerID=40&md5=4efc67db14c608fb29638c5a5f5d28a2
AFFILIATIONS: Istituto Nazionale di Geofisica e Vulcanologia, sezione di Catania, Piazza Roma 2, Catania, 95123, Italy; 
Center for the Study of Environmental Change, Department of Biological Sciences, Le Moyne College, Syracuse, 13214, United States
ABSTRACT: In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper, late-deposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity. We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Accretionary lapilli;  Diatreme;  Hyaloclastite;  Maar;  Volcaniclastic
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Vázquez, G.a , Ortega, B.b , Davies, S.J.c , Aston, B.J.c 
Sedimentary record of the last ca. 17000 years from Lake Zirahuen, Michoacan, Mexico [Registro sedimentario de los últimos ca. 17000 años del lago de Zirahuen, Michoacán, México]
(2010) Boletin de la Sociedad Geologica Mexicana, 62 (3), pp. 325-343. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650471977&partnerID=40&md5=047da1c8558fe5daa92360f53b8a723a
AFFILIATIONS: Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, México, D.F. 04510, Mexico; 
Instituto de Geofísica, Universidad Nacional Autónoma de México, México,D.F. 04510, Mexico; 
Institute of Geography and Earth Science, Aberystwyth University, Aberystwyth, Gales, Reino Unido, SY23 3DB, United Kingdom
ABSTRACT: Lake Zirahuen (101° 44' W, 19° 26' N), located in a volcanically active region at the boundary of the two major modern climatic systems (the intertropical convergence zone and the subtropical high pressure zone) and in a region with a history of human occupation of several thousand years, provides the opportunity to investigate climatic variations, the history of vegetation and the volcanic and anthropogenic impact in central Mexico. In this paper, we present a preliminary model of lacustrine evolution of Zirahuen Lake for the last 17000 cal yr BP, based on the analysis of vertical and lateral variations of this sedimentary deposit, using two sediment cores collected in the center and northern part of the lake (5.40 and 6.61 m depth). The described sedimentary facies have been grouped into four facies associations, which describe the sedimentary evolution of the central-north part of the lake. Core log correlation is supported by matching the magnetic susceptibility peaks. The chronological framework is provided by twenty 14C dates and the recognition of two historical tephras from Jorullo and Paricutin volcanoes. According to the age models, the northern sedimentary sequence spans ca. 17000 cal yr BP, while the central one covers 11540 cal yr BP. The facies are composed of diatomaceous ooze (massive or laminated), clastic facies and volcaniclastic facies. In the northern sequence, stratigraphical and chronological evidence point to a sedimentary hiatus of nearly 1 m, equivalent to 5000 yr. In consequence, the two sedimentary sequences are only correlated for the last 7200 cal yr BP. The evolution of Zirahuen Lake for the last 17000 yr as inferred from the variations in the sedimentary components is summarized in four stages: 1) 17000-14000 cal yr BP-low lake levels and dominance of fine-grained clastic sedimentation; 2) 14000-8180 cal yr BP-increase in lake level and littoral expansion under relatively stable conditions, and between 8180 and 7200 cal yr BP, an erosive event that gave origin to the hiatus in the northern sedimentary sequence; 3) 8180-3900 cal yr BP-lake level increases; and 4) the last 3900 yr are characterized by intense erosion and clastic sedimentation. Sporadic heavy precipitation over land with scarce vegetation probably induced the high erosion. For this period, it is difficult to separate the climatic and anthropogenic signals, as agriculture and other human land uses have been documented for the region. A low erosion period is recognized between 1400 and 800 yr ago, suggesting the extension of dry conditions inferred from other sites in Mesoamerica at the end of the archaeological Classic period.
AUTHOR KEYWORDS: Central mexico;  Holocene;  Lacustrine sediments;  Late pleistocene;  Paleolimnology;  Tephras
DOCUMENT TYPE: Article
SOURCE: Scopus

Khalaf, E.E.D.A.H.
Origin and evolution of post-collisional volcanism: an example from Neoproterozoic Dokhan volcanics at Gabal Nugara area, Northeastern Desert, Egypt
(2010) Arabian Journal of Geosciences, pp. 1-33. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650291567&partnerID=40&md5=41db6737b277f7f5f27381aad99c51a2
AFFILIATIONS: Geology Department, Faculty of Science, Cairo University, Giza, Egypt
ABSTRACT: Nugara volcanics are one of the northernmost outcrops of the Arabian-Nubian Shield. Two distinct volcanic successions are found in the Nugara basin: (1) old volcanic sequence composed of voluminous medium- to high-K calc-alkaline lavas and minor alkali basalt and (2) young volcanic sequence composed of subordinate tholeiitic mafic lavas. Their eruptions were punctuated by occasional volcaniclastic deposits that generated fall, flow, or reworked suites compositionally identical to the lava flows. These volcanics are a part of a post-subduction and extensional-related magmatic event in Northeastern Desert of Egypt. The volcanic rocks of the Nugara basin are characterized by strong enrichment in LILE relative to HESF, high LILE/HFSE ratios, and depletions of Nb on MORB-normalized multi-element diagrams. The geochemical features of the volcanic rocks suggest that they experienced fractional crystallization, along with mixing processes. Crustal contributions to the magma sources may also have occurred during magmatic evolution. These processes have resulted in scattered major and trace element variations with respect to increasing silica contents. The model proposed for their origin involves contrasting ascent paths and differentiation histories through crustal columns with different thermal and density gradients. The geochemical features of the most mafic samples suggest that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the East and West Gondwanaland. The volcanic activity in the region is best explained by the delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction-related processes. © 2010 Saudi Society for Geosciences.
AUTHOR KEYWORDS: Dokhan volcanics;  Gabal Nugara area;  Geochemistry;  Geodynamic implication;  Petrogenesis
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

de Vries, S.T., Nijman, W., de Boer, P.L.
Sedimentary geology of the Palaeoarchaean Buck Ridge (South Africa) and Kittys Gap (Western Australia) volcano-sedimentary complexes
(2010) Precambrian Research, 183 (4), pp. 749-769. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78649443469&partnerID=40&md5=c1c8c1c3172b0dfa91580567a192e150
AFFILIATIONS: Sedimentology Group, Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands
ABSTRACT: The two Palaeoarchaean volcano-sedimentary complexes of the Buck Ridge (Barberton Greenstone Belt, South Africa) and Kittys Gap (Coppin Gap Greenstone Belt, East Pilbara, Australia) have a similar geological setting and age (~3.45. Ga). The predominantly volcaniclastic sediments are concentrated at the top of these complexes, and experienced thorough, (very) early diagenetic silicification. In many places the silicification process has led to excellent preservation of the primary sedimentary structures. Elsewhere it has resulted in their obliteration or replacement by diagenetic structures. The Buck Ridge chert forms a regressive-transgressive succession, deposited around base level, with lacustrine and littoral marine facies. Deposition of the Kittys Gap Chert was also close to base level, almost exclusively subaqueous, with tidal influence and a regressive sequential trend.In both volcano-sedimentary complexes, these low-energy sediments are juxtaposed with high-energy breccia pods and layers, with often a high Fe-oxide content. The breccias are interpreted as being the result of explosive hydrothermal activity. Sedimentation was strongly controlled by normal faulting. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Archaean sedimentary basins;  Archean sedimentology;  Barberton Greenstone Belt;  Chert;  Coppin gap greenstone belt;  East pilbara granite-greenstone terrane
DOCUMENT TYPE: Article
SOURCE: Scopus

Martini, M.a , Ferrari, L.b , López-Martínez, M.c , Valencia, V.d 
Stratigraphic redefinition of the Zihuatanejo area, southwestern Mexico [Redefinición estratigráfica del área de Zihuatanejo, suroeste de México]
(2010) Revista Mexicana de Ciencias Geologicas, 27 (3), pp. 412-430. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78649700781&partnerID=40&md5=9a59c99b6b7d04fd263567180609f482
AFFILIATIONS: Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, México D.F. 04510, Mexico; 
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Blvd. Juriquilla 3001, 76230, Querétaro, Mexico; 
Laboratorio de Geocronología, División de Ciencias de la Tierra, CICESE, Carr. Ensenada-Tijuana 3918, 22860 Ensenada, Baja California, Mexico; 
Department of Geosciences, University of Arizona, Tucson AZ 85721, United States
ABSTRACT: The Mesozoic volcano-sedimentary successions exposed in southwestern Mexico have been traditionally grouped into the Guerrero terrane, and interpreted to represent an allochthonous long-lived island arc or a complex multi-arc system accreted to the continental margin of North America. However, the nature of these arcs (intraoceanic versus continental), as well as the timing of the supposed accretion, are still debated. One of the key regions in this debate is that of Zihuatanejo, where a Cretaceous island arc (Zihuatanejo arc) and associated accretionary complex (Las Ollas Complex) have been defined in the past. In this paper we present a redefinition of the stratigraphy of the Zihuatanejo region, based on field mapping supported by new 40Ar/39Ar and U-Pb geochronology, which has significant implications for the Cretaceous-Paleogene evolution of the Guerrero terrane. The lowermost stratigraphic levels of the Zihuatanejo region are represented by the pre-Cretaceous polydeformed and partly metamorphosed rocks of the Las Ollas Complex and Lagunillas Formation. These rocks are unconformably overlain by the Early Cretaceous shallow marine Playa Hermosa arc assemblage. Volcanic rocks of this assemblage are restricted to a few meters of andesitic lavas interbedded with volcaniclastic sandstone and limestone, which suggests that the study area was in a peripheral position with respect to the main axis of a magmatic arc. The rocks of the Playa Hermosa assemblage were uplifted by folding, eroded, and unconformably overlain by Upper Cretaceous continental to shallow marine rocks of the La Unión-Zihuatanejo assemblage, which are only gently folded. Similar continental rocks (Cutzamala Formation) are exposed in the Huetamo area, ~80 km northeast of Zihuatanejo, and are interpreted as overlapping successions of the Guerrero terrane. Based on this correlation, we propose that the Upper Cretaceous La Unión-Zihuatanejo assemblage is not part of the tectono-stratigraphic Guerrero terrane but rather constitute an overlap succession that post-dates the possible accretion of this terrane to nuclear Mexico. Finally, the Mesozoic rocks of the Zihuatanejo area are intruded by 48-40 Ma granitoids, and unconformably overlain by 41-39 Ma horizontally bedded volcanic and volcaniclastic rocks, which post-date the final contractile deformation in the Zihuatanejo area.
AUTHOR KEYWORDS: Guerrero terrane;  La Unión-Zihuatanejo assemblage;  Mexico;  Stratigraphy;  Zihuatanejo
DOCUMENT TYPE: Article
SOURCE: Scopus

Palladino, D.M., Simei, S., Sottili, G., Trigila, R.
Integrated approach for the reconstruction of stratigraphy and geology of Quaternary volcanic terrains: An application to the Vulsini volcanoes (central Italy)
(2010) Special Paper of the Geological Society of America, (464), pp. 63-84. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650918321&partnerID=40&md5=cb419625cd5c3eea0e95ab01df99bdba
AFFILIATIONS: Dipartimento di Scienze della Terra, Università La Sapienza, Rome 00185, Italy
ABSTRACT: Modern stratigraphic studies and field mapping of Quaternary volcanic terrains require a multidisciplinary approach for the reconstruction of the time-space history of a volcanic area (e.g., activity phases, eruptive sources, compositional changes, volcano build-up and collapse events) within the framework of concomitant and/or genetically related geological events acting on regional to global scales (e.g., tectonism, climate changes, glacio-eustatism). Here, we report recent results on the stratigraphy, structure, and evolution of the southern part of the Vulsini volcanic district (0.6-0.1 Ma), Roman Province, in the light of a new geological survey for the 1:50,000 map of Italy (CARG Project). We focus on the integration of different kinds of stratigraphic units, including lithostratigraphic, lithosomatic, and unconformitybounded stratigraphic (UBS) units, to define and group mappable volcanic bodies. Lithostratigraphic units are characterized in terms of textural features, indicative of eruptive and emplacement scenarios, and rock-type compositions. The intervening stratigraphic discontinuities are defined in terms of nature, position, and areal extent, and they are attributed to local depositional processes versus significant temporal hiatuses in the eruptive activity or regional and interregional geological events. The mapped volcanic units are thus correlated to lithosomatic units, corresponding to volcanic source edifices, as well as to the local and regional UBS unit settings recently defined for the Tyrrhenian coast nearby. On these grounds, we illustrate the geological evolution of the study area as the interplay of constructional and destructional volcanic activity, erosion, pedogenesis, secondary volcaniclastic sedimentation during intereruptive periods, and sea-level fluctuations. © 2010 The Geological Society of America. All rights reserved.
DOCUMENT TYPE: Article
SOURCE: Scopus

Iryu, Y.a , Takahashi, Y.b , Fujita, K.c , Camoin, G.d , Cabioch, G.e , Matsuda, H.f , Sato, T.g , Sugihara, K.h , Webster, J.M.i , Westphal, H.j 
Sealevel history recorded in the Pleistocene carbonate sequence in IODP Hole 310-M0005D, off Tahiti
(2010) Island Arc, 19 (4), pp. 690-706. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78649692104&partnerID=40&md5=92f8d144d2fecb293b0ac2e515853159
AFFILIATIONS: Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan; 
Institute of Geology and Paleontology, Graduate School of Science, Tohoku University, Aobayama, Sendai 980-8578, Japan; 
Department of Physics and Earth Sciences, University of the Ryukyus, Okinawa 903-0213, Japan; 
Centre Europeen de Recherche et d'Enseignement des Geosciences de l'Environnement (CEREGE), UMR 6635 CNRS, Europôle Méditerranéen de l'Arbois, BP 80, F-13545 Aix-en-Provence Cedex 4, France; 
Institut de Recherche pour le Déloppement, Bondy Cedex, France; 
Department of Earth Sciences, Graduate School of Technology and Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan; 
Institute of Applied Earth Sciences, Faculty of Engineering and Resource Science, Akita University, Teagata-Gakuencho 1-1, Akita 010-8502, Japan; 
Center for Global Environmental Research (CGER), National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan; 
School of Geosciences, The University of Sydney, Sydney, NSW, 2006, Australia; 
MARUM, Center for Marine Environmental Sciences, Universität Bremen, Leobener Straße, 28359 Bremen, Germany
ABSTRACT: Material cored during the Integrated Ocean Drilling Program (IODP) Expedition 310 'Tahiti Sea Level' revealed that the fossil reef systems around Tahiti are composed of two major stratigraphic sequences: (i) a last deglacial sequence; and (ii) an older Pleistocene sequence. The older Pleistocene carbonate sequence is composed of reef deposits associated with volcaniclastic sediments and was preserved in Hole 310-M0005D drilled off Maraa. Within an approximately 70-m-thick older Pleistocene sequence (33.22-101.93 m below seafloor; 92.85-161.56 m below present sealevel) in this hole, 11 depositional units are defined by lithological changes, sedimentological features, and paleontological characteristics and are numbered sequentially from the top of the hole downward (Subunits P1-P11). Paleowater depths inferred from nongeniculate coralline algae, combined with those determined by using corals and larger foraminifers, suggest two major sealevel rises during the deposition of the older Pleistocene sequence. Of these, the second sealevel rise is associated with an intervening sealevel drop. It is likely that the second sealevel rise corresponds to that during Termination II (TII, the penultimate deglaciation, from Marine Isotope Stages 6 to 5e). Therefore, the intervening sealevel drop can be correlated with that known as the 'sealevel reversal' during TII. Because there are limited data on the Pleistocene reef systems in the tropical South Pacific Ocean, this study provides important information about Pleistocene sealevel history, the evolution of coral reef ecosystems, and the responses of coral reefs to Quaternary climate changes. © 2010 Blackwell Publishing Asia Pty Ltd.
AUTHOR KEYWORDS: DP Hunter;  Hole M0005D;  IODP Expedition 310 'Tahiti Sea Level';  Pleistocene;  Sealevel change;  Tahiti
DOCUMENT TYPE: Article
SOURCE: Scopus

Brinton, D., Moore, J., McLennan, J., Jones, C.
Predicting thermal conductivity of geothermal reservoir rocks
(2010) AIChE Annual Meeting, Conference Proceedings, . 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78751537204&partnerID=40&md5=cb11d399105c134c24dcf12481c83956
ABSTRACT: Understanding rock temperatures and stress fields will be important in predicting fracture behavior during enhanced geothermal reservoir development. For many geothermal reservoirs, thermophysical property data (coefficients of thermal expansion, thermal conductivity and specific heat) are limited. Thermal conductivity, diffusivity and specific heat are relevant for quantifying the power potential and forecast for prospective and operating geothermal plants and govern the way temperature gradients move through the reservoir. The coefficient of thermal expansion and certain other mechanical parameters of the reservoir such as Young's modulus and Poisson's ratio intrinsically contribute to thermal alteration of in-situ stresses in response to temperature perturbations during reservoir development by hydraulic fracturing and during heat production. Recognizing the lack of a substantial database of thermophysical properties, standard geophysical well logs and mineralogic analysis of core and cuttings from the Raft River Geothermal Field have been used to predict thermal conductivity. Predictions are compared with the experimentally-determined values from core samples collected from Raft River Geothermal well RRG-3C. The work will support ongoing investigations to thermally and hydraulically stimulate well RRG-9 under a US DOE sponsored grant. RRG-9 was drilled to 6089 feet measured depth (MD) in the Raft River Geothermal Field located in southern Idaho, near the Idaho-Utah state line. The field lies within the Basin and Range province. In the 1970s to early 1980s, the field was the site of intense study by the US Department of Energy. During that period a significant amount of geologic and reservoir data were collected. The reservoir is developed in Precambrian metamorphic and granitic rocks beneath approximately 5000 ft of Tertiary volcaniclastic deposits. U.S. Geothermal, Inc. operates a 13-MW plant at the site.
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

McCann, T., Siemes, A., Fischer, A., Ebinghaus, A., Temme, A.
Sediment fill and fault activity in the Mesta Basin (SW Bulgaria)
(2010) Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen, 258 (3), pp. 365-379. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651099256&partnerID=40&md5=39ad6584329b205c495e742ee555c23b
AFFILIATIONS: Geologisches Institut, Universität Bonn, Nußallee 8, 53115 Bonn, Germany
ABSTRACT: The NNW-SSE-oriented Mesta Basin (SW Bulgaria) is located between the Pirin and Rhodope massifs. The basin contains a thick Palaeogene-age succession comprising mainly siliciclastics and volcaniclastics deposited in a continental setting. Associated volcanic rocks were sourced from a series of volcanoes in the southern part of the basin. Analysis of the dip configurations within a series of stratigraphie sections across the basin reveals that there is a progressive decrease in the stratigraphie gradient from the older through to the younger stratigraphic levels, and that this probably resulted from the complex interaction of (1) the amount of sediment input in relation to the emergence of the volcanic system, and (2) the degree of rotation due to the possible listric detachment fault (i.e. Mesta Detachment). © 2010 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
AUTHOR KEYWORDS: Alluvial fan;  Bulgaria;  Dip;  Mesta basin;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Tahir, S., Musta, B., Rahim, I.A.
Geological heritage features of Tawau volcanic sequence, Sabah
(2010) Bulletin of the Geological Society of Malaysia, (56), pp. 79-85. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78751483323&partnerID=40&md5=2d2c222ead804d09dba03987209e67fc
AFFILIATIONS: Geology Programme, School of Science and Technology, Universiti Malaysia Sabah, 88999 Kota Kinabalu, Sabah, Malaysia
ABSTRACT: Semporna Peninsula area was built up by thick Tertiary sequence of volcanic flows and volcaniclastic rocks. Early Cretaceous tholeiite basalt is the oldest sequence of volcanic rocks interpreted to have formed as part of a wide spread submarine volcano or volcanic complex within an MORB characterized by rapid volcanism. Miocene to Quaternary volcanisms from volcanic arcs contributed sequences of lava flows and pyroclastic rocks of dacitic, andesitic and basaltic rock types forming the major mountain chains of southeast Sabah. This Neogene volcanic sequence is dominated by low to high K-calc alkaline andesitic to dacitic volcanic rocks similar to modern island arc type. The subaerial of the latest lava flows of the region indicates volcanism consistent with tholeiitic basalt type. It has been accepted that during the Cenozoic, Sabah has been subjected to series of major tectonic regimes. A number of deformation phases have been determined include: Middle Eocene, Middle Miocene and Plio-Pleistocene phases of crustal movements of this region. The area appeared, therefore, to have been subjected to compressional tectonic regime throughout much of the late Cenozoic. However, the structural and sedimentological expression of these tectonic regimes varies considerably. It is suggested here that compressional episodes were interspersed with periods of active transtensional basin formation and that Late Miocene extension of the eastern part of Sabah which was related to compressional forces. On the basis of geological data and kinematic reconstructions, two types of island arcs can be differentiated: those related to the progressive closing of the Celebes and Sulu marginal basins during Middle Miocene and those belonging to the south Philippine Sea Plate during Plio-Pleistocene. The combined age and chemistry for these two magmatic belts allow us to decipher the Tertiary evolution of the complex zone of interaction of the Semporna Peninsula and the surrounding areas. This Tertiary sequence is underlain by the Early Cretaceous pillow lava basalt, and culminated by the late Pleistocene volcanisms those contributing to the major topography of the area include Andrassy, Lucia, Maria, Wullersdorf and Magdalena mountains formed the prominent topographic features of the area. This youngest volcanic apron covers an extensive area of the Semporna Peninsula. Semporna volcanic associations form important link with the long chain of Tertiary volcanic activities in this region that extend from the Sulu Archipelago, Philippines to the southeastern part of Sabah.
AUTHOR KEYWORDS: Geological heritage;  Pleistocene volcanic sequence;  Semporna Peninsula;  Tawau hills
DOCUMENT TYPE: Article
SOURCE: Scopus

Viereck-Goette, L.a , Lepetit, P.a , Gürel, A.b , Ganskow, G.c , Çopuroǧlu, I.b , Abratis, M.a 
Revised volcanostratigraphy of the upper Miocene to lower Pliocene Ürgüp Formation, Central Anatolian volcanic province, Turkey
(2010) Special Paper of the Geological Society of America, (464), pp. 85-112. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650869614&partnerID=40&md5=2b4accd9319d8d192d73b966cce07860
AFFILIATIONS: Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, D-07749 Jena, Germany; 
Department of Geological Engineering, Niǧde Üniversitesi, TR-51100 Niǧde, Turkey; 
Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany
ABSTRACT: Results are presented of fieldwork and laboratory analyses on the volcanostratigraphy of the Ürgüp Formation in the Central Anatolian volcanic province, Cappadocia, Turkey. The formation of late Miocene to early Pliocene age is exposed in areas of the Ürgüp Basin and Nevşehir Plateau. It consists of volcaniclastic and epiclastic members with intercalated local basaltic to andesitic lava flows and scoria. The volcaniclastic members are composed of widespread covers of voluminous rhyolitic, less often dacitic, low-aspect ignimbrites and unconsolidated Plinian air-fall pumice layers. Intercalated abundant terrestrial and/or lacustrine sedimentary successions occur, which are dominated by lahars in the south and carbonates or diatomites in the north, respectively. Based on field, mineralogical, and geochemical evidence, a number of revisions are suggested by our studies, two of which are presented and discussed here: (1) the new correlation of the former "Sofular Ignimbrite" with the ignimbritic bed of the Sarimaden Tepe Member, and (2) the identification of a widespread pair of Plinian air-fall pumice lapilli beds, tentatively called Güzel Dere Member. It can be correlated with the former stratigraphic units "Tilköy Fall" and "Karain Fall." The Tilköy Fall is recognized as a local remnant in an unconformity-bounded stratigraphic profile, and the Karain Fall unit is recognized as a set of reworked pumice-enriched layers in a lacustrine sediment pile. From complete terrestrial sediment sections, we identified the stratigraphic position of the Güzel Dere Member between the ignimbritic Cemilköy and Tahar Members. The pumice layers provide a new marker horizon for external epiclastic profiles in Central Anatolia not reached by ignimbrites. © 2010 The Geological Society of America. All rights reserved.
DOCUMENT TYPE: Article
SOURCE: Scopus

Allibone, A.a , Ashley, P.b , Mackenzie, D.c , Craw, D.c 
Shear-hosted base metal mineralisation at the Dana Peaks, Murchison Mountains, Fiordland, New Zealand
(2010) New Zealand Journal of Geology and Geophysics, 53 (4), pp. 271-294. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79955730483&partnerID=40&md5=1f276e406173a57ea5969c8c061ecc31
AFFILIATIONS: Rodinian Pty Ltd., Queanbeyan, NSW, Australia; 
Earth Sciences, University of New England, Armidale, NSW, Australia; 
Department of Geology, University of Otago, Dunedin, New Zealand
ABSTRACT: Darran Suite dioritic, tonalitic and granodioritic plutonic rocks and schistose Loch Burn Formation volcaniclastic rocks in the central Murchison Mountains at the Dana Peaks have been affected by widespread biotite-sericite-chlorite-albite-quartzpyrite ± carbonate ± epidote/clinozoisite ± titanite/rutile ± actinolite alteration. More intense, paler coloured sericite-albitequartz-pyrite ± carbonate alteration is concentrated along orange weathered shear zones. Alteration assemblages are transitional between those commonly referred to as propylitic, potassic and phyllic. Altered rocks contain anomalous concentrations of copper, lead, zinc and silver over an area of c. 2.5 × 6 km. Metal concentrations 2-5 times those typical of Darran Suite plutonic rocks and the Loch Burn Formation are commonly associated with more extensive weak to moderate intensity alteration. Higher metal grades up to c. 0.5% copper, 1% zinc, 1.3% lead and 30ppm silver are concentrated in or adjacent to the 1-5m wide, more intensely altered shear zones which contain entrained lenses of pyritised country rock, breccias and quartz ± K-feldspar ± chlorite ± carbonate ± hematite ± tourmaline veins. Some mineralised rocks also contain traces of tungsten (2-7 ppm), arsenic (<5-35ppm) and tellurium (0.2-5.4ppm). Most samples lack detectable molybdenum (<3ppm), gold (<0.004ppm) or bismuth (<0.2ppm), with atypical higher values (40,0.03 and 50ppm, respectively) generally restricted to the most intensely altered and/or deformed rocks. The mineralised rocks show a close spatial and temporal relationship with several narrow ductile shear zones that probably developed in the Early Cretaceous between c. 128 and 110 Ma. Mineralised shear zones form minor splays off larger shear zones that are part of a major intra-arc fault system, active along or near the boundary between inboard and outboard parts of the Median Batholith at this time. Traces of similar lead mineralisation are present at the head of the Mid Burn c. 8 km to the northeast along strike on the same regional-scale fault system as the Dana Peaks locality. Fluids and metals are likely to have been derived from metamorphism of the Loch Burn Formation and/or adjacent plutonic rocks. A magmatic hydrothermal origin is considered unlikely as the metal assemblage lacks Mo, Bi, Au, Sn and W and the adjacent plutonic rocks probably crystallised several million years or more before alteration and mineralisation. © 2010 The Royal Society of New Zealand.
AUTHOR KEYWORDS: Copper;  Dana Peaks;  Dana tonalite;  Fiordland;  Lead;  Loch Burn Formation;  Murchison intrusives;  Murchison Mountains;  Plateau pluton;  Propylitic;  Pyrite;  Sericite;  Shear zone;  Silicification silver;  Zinc
DOCUMENT TYPE: Article
SOURCE: Scopus

Milia, A.
The stratigraphic signature of volcanism off Campi Flegrei (Bay of Naples, Italy)
(2010) Special Paper of the Geological Society of America, (464), pp. 155-170. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650942204&partnerID=40&md5=fecd6ee11d5b9cfc9493bc80be8e6f37
AFFILIATIONS: Istituto per l'Ambiente Marino Costiero (IAMC), Consiglio Nazionale delle Ricerche, Calata Porta di Massa, Porto di Napoli, I-80133 Naples, Italy
ABSTRACT: Seismic stratigraphic analysis of a submarine volcanic field allows the recognition of complex stratal architecture due to the interplay between the syneruptive and intereruptive stratigraphic units. This approach was applied to the offshore Campi Flegrei, eastern Tyrrhenian Sea margin. The area features Late Quaternary volcanism, shallow magmatic intrusions, and thick intereruptive volcaniclastic wedges. Seismic stratigraphic analysis is constrained by marker seismic reflectors defining volcanic boundaries and tied to wells drilled in Naples city, cropping out volcanic units, and a chronostratigraphic framework recognized within the Bay of Naples succession. On the basis of seismic configuration, it was possible: (1) to detect various typologies of magmatic features, such as scoria cones, tuff cones, domes, dikes, and pyroclastic flows; (2) to recognize three types of unconformities; and (3) to reconstruct the relation between monogenetic volcanoes and intereruptive sedimentary units. The eruptions of monogenetic volcanoes deeply modified the paleogeography of the Bay of Naples, transforming an intraslope basin into smaller basins separated by volcanic ridges. The former were successively filled during the intereruptive periods. The sediments eroded in the shoreface and subaerial environment were deposited along the volcano margins. Prograding wedges were deposited during the fall of sea level and filled the seaways between volcanoes, whereas during the rising of the sea level, deposition migrated toward the volcano crater until the latter were drowned below sea level. This paper defines the stratigraphic evolution of the south margin of the Campi Flegrei volcanic field and provides both an example of seismostratigraphic analysis in a complex volcanic area and additional data for the volcanologic interpretation of the Campi Flegrei. © 2010 The Geological Society of America. All rights reserved.
DOCUMENT TYPE: Article
SOURCE: Scopus

El Kazzaz, Y.A.
Geometry of fold interference patterns in Wadi Kharit area, South Eastern Desert, Egypt
(2010) Egyptian Journal of Remote Sensing and Space Science, 13 (2), pp. 113-120. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952402845&partnerID=40&md5=7a886aca6c6fc30ec0ebbac05da3d9cd
AFFILIATIONS: Geology Department, Faculty of Science, Helwan University, Egypt
ABSTRACT: Fold interference patterns and superimposed relations are common in the Neoproterozoic basement rocks of Egypt. They are the products of complex Precambrian orogenies formed by collision and accretionary island arcs onto a pre-Pan-African continent to the west of the River Nile. Fold interference patterns and superimposed folds affected the unmetamorphosed to slightly metamorphosed volcaniclastic rocks in Wadi Kharit area during the Pan-African tectono-thermal events (600-450 Ma). Superimposed folding in Wadi Kharit area resembles in many respects that of recorded in Hafafit Shear Zone. The difference is in the degree of deformation and grade of metamorphism. Fold interference patterns and superimposition in Wadi Kharit area are formed by a single phase of deformation rather than a polyphase of deformation. Most of the fractures and associated normal faults dissected Wadi Kharit area are of fold-related faulting, which are reactivated post-dating igneous intrusions. © 2011 National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Fold interference patterns;  Folding and refolding;  Nappe structure;  Overturned fold
DOCUMENT TYPE: Article
SOURCE: Scopus

Prete, S.D.a , Iovine, G.b , Parise, M.c , Santo, A.d 
Origin and distribution of different types of sinkholes in the plain areas of Southern Italy
(2010) Geodinamica Acta, 23 (1-3), pp. 113-127. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-79952258984&partnerID=40&md5=d52c3332dcf24948ebb7b299d7739af8
AFFILIATIONS: Campania Speleological Federation, Caserta, Italy; 
Research Institute for Geo-Hydrologic Protection, National Research Council, Cosenza, Italy; 
Research Institute for Geo-Hydrologic Protection, National Research Council, Via Amendola 122-I, 70126, Bari, Italy; 
Dept. Hydraulic, Geotechnical and Environmental Engineering, University Federico II, Naples, Italy
ABSTRACT: Sinkholes constitute a significant risk in many karst areas, and may even, threat human safety, Collapse sinkholes that occur catastrophically without showing premonitory signs may result in severe economic losses and casualties. In the last years, research on sinkholes and related detrimental effects has significantly increased in Italy, in the aftermath of remarkable events. Aimed at analysing the peculiar conditions which lead to sinkhole occurrence in Southern Italy, a set of cases in the plain areas of Campania, Apulia and Calabria is discussed, The considered regions show a wide variety of environmental conditions. In Campania, the plains are underlain by alluvial deposits with, intercalations of volcaniclastic sediments. Sinkholes are generally located along the Tyrrhenian margin, of the carbonate massifs or within intramontane Apennine basins. In Apulia, a flat and elongated, peninsula, most of the cases occur on calcarenites overlying limestone bedrock along the coast. In Calabria, one of the most seismogenic Italian regions, the surveyed cases seem to be attributable mainly to earthquake-induced liquefaction. The article provides a first glance on the variety of sinkholes in the plain areas of Southern Italy, to highlight the possibility of further subsidence events in the considered regions, as well as in other comparable areas of the country. © 2010 Lavoisier SAS. All rights reserved.
AUTHOR KEYWORDS: Earthquake;  Hazard;  Italy;  Plain areas;  Sinkhole
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

Erkül, F.a , Erkül, S.T.b , Helvaci, C.c 
Petrographic and geochemical analyses of Early Miocene volcanic units in the Bigadiç borate basin, western Anatolia-Turkey: Evidences of magma mixing/mingling processes [Erken Miyosen Bigadiç bor havzasi{dotless}ndaki volkanik birimlerin petrografik ve jeokimyasal özellikleri: Magma kari{dotless}şi{dotless}mi{dotless}ni{dotless}n kani{dotless}tlari{dotless}, Bati{dotless} Anadolu-Türkiye]
(2010) Yerbilimleri/ Earth Sciences, 31 (2), pp. 141-168. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651496450&partnerID=40&md5=21cd30ac629acc87c9b9eeab93d5c0b5
AFFILIATIONS: Akdeniz Üniversitesi, Teknik Bilimler Meslek Yüksekokulu, 07058, Antalya, Turkey; 
Akdeniz Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisliǧi Bölümü, 07058, Antalya, Turkey; 
Dokuz Eylül Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisliǧi Bölümü, Izmir, Turkey
ABSTRACT: The NE-trending Bigadiç borate basin is one of the regions that have well-exposed Cenozoic calc-alkaline and alkaline volcanic associations in western Anatolia. Age of basalt to rhyolitic volcanic associations within the basin is between 23 and 17.8 Ma. The Early Miocene successions in the Bigadiç region are represented by lacustrine, evaporitic and fluvial deposits intercalated with lavas and volcaniclastic rocks which were extruded along NEtrending volcanic centres. These volcanic rocks, formed in two distinct episodes, are divided into five units based on their lithological, petrographical and compositional characteristics such as Kocaiskan volcanic unit, Gölcük basalt, Si{dotless}ndi{dotless}rgi{dotless}, Kayi{dotless}rlar and Şahinkaya volcanic units. Volcanic units, except for the Gölcük basalt, contain abundant ellipsoidal enclaves with variable sizes ranging from a few millimetres to centimetres. Kocaiskan, Si{dotless}ndi{dotless}rgi{dotless}, Kayi{dotless}rlar and Şahinkaya volcanic units are calc-alkaline and medium to high-K, while the Gölcük basalt has mildly alkaline nature with high-K. Rare earth element (REE) patterns of the calc-alkaline volcanic units display similar characteristics to each others, distinct fractionation from light rare earth element (LILE) to heavy rare earth element (HREE). However, mildly alkaline Gölcük basalt is characterised by minor enrichment and relatively flat patterns in REE spider diagrams. Bimodal volcanism, which is defined by the association of the mildly alkaline and calc-alkaline associations, was formed by magma mixing/mingling processes that operated on the mantle- and crust-derived magma sources.
AUTHOR KEYWORDS: Bigadiç;  Crust and mantle magma origin;  Mafic microgranular enclave;  Mildly alkaline-calcalkaline;  Miocene;  Mixing textures
DOCUMENT TYPE: Article
SOURCE: Scopus

McNicoll, V.a , Squires, G.b , Kerr, A.c , Moore, P.d 
The duck pond and boundary Cu-Zn deposits, newfoundland: New insights into the ages of host rocks and the timing of vhms mineralization
(2010) Canadian Journal of Earth Sciences, 47 (12), pp. 1481-1506. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78650440676&partnerID=40&md5=01f39d1d8371f8a3c345da622ef0781f
AFFILIATIONS: Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada; 
Teck Resources Ltd, P.O. Box 9, Millertown, NL A0H 1V0, Canada; 
Geological Survey of Newfoundland and Labrador, P.O. Box 8700, St. John's, NL A1B 4J6, Canada; 
Royal Roads Corporation, Suite E-130, 120 Torbay Road, St. John's, NL A1A 2G8, Canada
ABSTRACT: The Duck Pond Cu-Zn-Pb-Ag-Au deposit in Newfoundland is hosted by volcanic rocks of the Cambrian Tally Pond group in the Victoria Lake supergroup. In conjunction with the nearby Boundary deposit, it contains 4.1 million tonnes of ore at 3.3% Cu, 5.7% Zn, 0.9% Pb, 59 g/t Ag, and 0.9 g/t Au. The deposits are hosted by altered felsic flows, tuffs, and volcaniclastic sedimentary rocks, and the sulphide ores formed in part by pervasive replacement of unconsolidated host rocks. U-Pb geochronological studies confirm a long-suspected correlation between the Duck Pond and Boundary deposits, which appear to be structurally displaced portions of a much larger mineralizing system developed at 509 ± 3 Ma. Altered aphyric flows in the immediate footwall of the Duck Pond deposit contained no zircon for dating, but footwall stringer-style and disseminated mineralization affects rocks as old as 514 ± 3 Ma at greater depths below the ore sequence. Unaltered mafic to felsic volcanic rocks that occur structurally above the orebodies were dated at 514 ± 2 Ma, and hypabyssal intrusive rocks that cut these were dated at 512 ± 2 Ma. Some felsic samples contain inherited (xenocrystic) zircons with ages of ca. 563 Ma. In conjunction with Sm-Nd isotopic data, these results suggest that the Tally Pond group was developed upon older continental or thickened arc crust, rather than in the ensimatic (oceanic) setting suggested by previous studies.
DOCUMENT TYPE: Article
SOURCE: Scopus

Hildebrand, R.S.a , Hoffman, P.F.b , Housh, T.c  e , Bowring, S.A.d 
The nature of volcano-plutonic relations and the shapes of epizonal plutons of continental arcs as revealed in the Great Bear magmatic zone, northwestern Canada
(2010) Geosphere, 6 (6), pp. 812-839. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-79251565254&partnerID=40&md5=c476e691d0f2056ba936770378f12b25
AFFILIATIONS: Department of Geology, University of California, One Shields Avenue, Davis, CA 95616-8605, United States; 
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States; 
Department of Geological Sciences, The University of Texas at Austin, 1 University Station C1100, Austin, TX 78712-0254, United States; 
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Building 54-1126, Cambridge, MA 02139, United States; 
School of Earth and Ocean Sciences, University of Victoria, Box 1700, Victoria, BC V8W 2Y2, Canada
ABSTRACT: The shapes of plutons and their emplacement mechanisms, the connection between the volcanic and plutonic realms, and the development of batholiths have been of interest to geologists since they realized that plutons were once low viscosity magma. These issues have proven difficult to resolve because there are few places that have enough relief to expose the critical relations. The Great Bear magmatic zone, a Paleoproterozoic continental arc located in northern Canada's Wopmay orogen, provides an informative field setting to resolve some of these issues because the rocks are generally non-metamorphosed and were broadly folded such that calderas, stratovolcanoes, and a wide variety of plutons are exposed in oblique cross-section on fold limbs in an area of subdued topographic relief. Early mafic plutons intruded co-magmatic pillow basalt piles as thin sheets with aspect ratios of 10-15. Plutons of intermediate composition, temporally associated with andesitic stratocones, have flat or slightly domical roofs and flat floors, and aspect ratios in the range of 5-10. Granodioritic to monzodioritic plutons that cut thick sequences of ashflow tuff and related volcaniclastic rocks are generally sheet-like bodies with aspect ratios of 10-20, except where they intrude calderas and form resurgent plutons. Granitic plutons intrude at slightly deeper crustal levels, are generally younger, and typically have miarolytic cavities, pegmatites, and associated dike swarms. The granites have flat roofs and floors but generally have lower aspect ratios than the intermediate composition plutons. Cycles-where magma bodies were first partially evacuated by eruption, then were re-energized and rose into their own ejecta to form plutons-span the compositional range from basalt to rhyodacite. The cycle of eruption, with the partial evacuation of chambers and subsequent rise of remaining magma to even higher levels in the crust explains why it is generally so difficult to link volcanic eruptions to specific plutons. The overall development of the Great Bear magmatic zone-from small-scale local eruptions of basalt to voluminous eruptions of intermediate composition ash-flow tuff followed by wide-scale emplacement of granitic plutons-is interpreted to represent input of subduction-related magmas, which led to progressive heating, melting, and wholesale upward differentiation of the crust beneath the arc. © 2010 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Dufresne, A.a , Salinas, S.b , Siebe, C.b 
Substrate deformation associated with the Jocotitlán edifice collapse and debris avalanche deposit, Central México
(2010) Journal of Volcanology and Geothermal Research, 197 (1-4), pp. 133-148. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956340873&partnerID=40&md5=8c585ed48bd2317f7a503b0a5a96f526
AFFILIATIONS: Department of Geological Sciences, Canterbury University, PB 4800, Christchurch, New Zealand; 
Departamento de Vulanología, Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico D.F., Mexico
ABSTRACT: An impressive debris avalanche deposit is preserved at Jocotitlán volcano in Central Mexico. The northern flank of this edifice collapsed ~9690yearsB.P. resulting in a 80km2-covering clast-supported deposit that lacks substantial matrix, fine, weak or hydrothermally altered materials. The deposit can be subdivided into three morphologically distinct areas which are each accompanied by specific, and often unique, deformation features in the underlying and adjacent volcaniclastic and lacustrine sediments. From these features, a complex history of pre- and syn-avalanche events was reconstructed beginning with edifice-spreading on the weak substrate material prior to and in preparation of part of the flank collapse event. The north-eastern flank in particular was strongly coupled with the deforming substrate material as is still evident in its extensional profile and the unique mode of failure during the catastrophic event resulting in the deposition of what resembles non-volcanic blockslide deposits rather than the typical hummocky volcanic debris avalanche morphology. This latter type of failure occurred at the north-western flank of Jocotitlán volcano where few signs of substrate interactions are preserved in a deposit dominated by large conical hummocks. In addition to substrate response, interaction with pre-avalanche topography in the eastern deposit area facilitated the emplacement of a lobe roughly perpendicular to the flank failure direction, at apparent high emplacement velocity, and with longitudinal ridges as its most striking surface expression. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Debris avalanche;  Jocotitlán;  Substrate deformation;  Volcano spreading
DOCUMENT TYPE: Article
SOURCE: Scopus

Van, A., Yalçinalp, B.
Geoloci{dotless}gal setti{dotless}ng and geochemical characteri{dotless}sti{dotless}cs of kuşkayasi{dotless} manganese deposi{dotless}t, otlukbeli, erzincan, türkiye [Kuşkayasi{dotless} (otlukbeli - erzincan) manganez yataǧi{dotless}ni{dotless}n jeolojik yerleşimi ve jeokimyasal özellikleri]
(2010) Jeoloji Muhendisligi Dergisi, 34 (1), pp. 41-56. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78549236842&partnerID=40&md5=6955b24f83081d079a878482ce34ef92
AFFILIATIONS: KTÜ Müh Fak, Jeoloji Müh. Bölümü, Trabzon, Turkey
ABSTRACT: İn the northern parts of Otlukbeli the volcaniclastic rocks which belong to Liassic aged Kelkit Formation, are found on the bottom. These rocks are overline by the Hozbirik Yayla limenstones which are formed by micritic limenstones of Malm-Lower Cretoceaus. The Otlukbeli Melange has been trusted on these limenstones and was formed and located in the Aptian and Albian. All o these units are cross cut by the Sari{dotless}han granitoid of Campanian age. Youngest unit of the area is the Sari{dotless}taşlar Formation, which composed of conglomerate,sansstone and shale alternation. The Mn mineralizationsin the area are found in the radiolarites within the Otlukbeli Melange. The most important of these mineralizationsis the Kuşkayasi{dotless} ore deposit. The vein shaped deposit is 180 m. İn length, 2 m. İn average thickness and has a width more than 40 m. in dip direction. The major ore minerals are braunite, pyrolusite, psilomelane, bixibite and manganite. The interpretation of geochemical diagrams prepared for major and trace elements contens revealed that the ore deposits was hydrothermal in origin. At present he ore deposits contains commercially more than 12.000 tons of Mn.
DOCUMENT TYPE: Article
SOURCE: Scopus

Zernack, A.V.a , Cronin, S.J.b , Neall, V.E.b , Procter, J.N.b 
A medial to distal volcaniclastic record of an andesite stratovolcano: detailed stratigraphy of the ring-plain succession of south-west Taranaki, New Zealand
(2010) International Journal of Earth Sciences, pp. 1-30. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78349253432&partnerID=40&md5=dc42bff45e233906b977bbdd457f238d
AFFILIATIONS: Laboratoire Magmas et Volcans, Université Blaise Pascal, 5 Rue Kessler, Clermont-Ferrand, 63038, France; 
Institute of Natural Resources, Massey University, Private Bag 11 222, Palmerston North, 4442, New Zealand
ABSTRACT: The >25 ka volcaniclastic ring-plain succession in south-west Taranaki has been remapped to establish a much more detailed understanding of the older stratigraphic record of Mt. Taranaki. Coastal cliff exposures show a range of volcaniclastic lithofacies, including debris-avalanche and lahar deposits, and allow a detailed chronological reconstruction of past volcanic and sedimentary events. Five new debris-avalanche deposits were identified, and their distribution in coastal cross-sections mapped. In addition, four previously described units were renamed and their stratigraphic position and lateral extent redefined. Chronostratigraphic control of the younger (<50 ka) sequence was obtained by radiocarbon dating of wood found within, or peat interbedded with, the deposits. Emplacement ages of the older units were estimated from their stratigraphic position and underlying marine wave-cut surfaces. Overall, at least 14 widespread debris-avalanche deposits occur within the <200 ka ring-plain record of Mt. Taranaki, suggesting one major edifice failure on average every 14,000 years, with an increase in frequency since 40 ka. The stratigraphic reconstruction of the ring-plain succession showed that the same pattern of deposition was repeatedly produced throughout the existence of Mt. Taranaki. Depending on their sedimentological characteristics, the different volcanic and sedimentary lithofacies can be related to phases of edifice-construction or collapse events. Based on the identified cyclic sedimentation pattern, we present a new episodic stratigraphy that integrates existing and new lithostratigraphic units into a coherent chronostratigraphic framework that can be applied to the entire volcanic and volcaniclastic succession at Mt. Taranaki. This model takes into account the complex geological processes that have taken place on the volcano and provides a more uniform stratigraphic terminology that could be applied to repeatedly collapsing stratovolcanoes elsewhere. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Andesite stratovolcano;  Debris-avalanche deposits;  Mt. Taranaki;  Ring-plain succession;  Volcanic stratigraphy;  Volcaniclastic
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Squire, R.J.a , Allen, C.M.b , Cas, R.A.F.a , Campbell, I.H.b , Blewett, R.S.c , Nemchin, A.A.d 
Two cycles of voluminous pyroclastic volcanism and sedimentation related to episodic granite emplacement during the late Archean: Eastern Yilgarn Craton, Western Australia
(2010) Precambrian Research, 183 (2), pp. 251-274. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78449285433&partnerID=40&md5=6aef2b93e38d263e49152dba8c51f5c4
AFFILIATIONS: School of Geosciences, Monash University, Clayton, VIC 3800, Australia; 
Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia; 
Predictive Mineral Discovery Co-operative Research Centre, C/o Geoscience Australia, GPO Box 378, Canberra, ACT 2609, Australia; 
Department of Applied Geology, Curtin University, Bentley, WA 6845, Australia
ABSTRACT: The thick piles of late-Archean volcaniclastic sedimentary successions that overlie the voluminous greenstone units of the eastern Yilgarn Craton, Western Australia, record the important transition from the cessation in mafic-ultramafic volcanism to cratonisation between about 2690 and 2655. Ma. Unfortunately, an inability to clearly subdivide the superficially similar sedimentary successions and correlate them between the various geological terranes and domains of the eastern Yilgarn Craton has led to uncertainty about the timing and nature of the region's palaeogeographic and palaeotectonic evolution. Here, we present the results of some 2025 U-Pb laser-ablation-ICP-MS analyses and 323 Sensitive High-Resolution Ion Microprobe (SHRIMP) analyses of detrital zircons from 14 late-Archean felsic clastic successions of the eastern Yilgarn Craton, which have enabled correlation of clastic successions. The results of our data, together with those compiled from previous studies, show that the post-greenstone sedimentary successions include two major cycles that both commenced with voluminous pyroclastic volcanism and ended with widespread exhumation and erosion associated with granite emplacement. Cycle One commences with an influx of rapidly reworked feldspar-rich pyroclastic debris. These units, here-named the Early Black Flag Group, are dominated by a single population of detrital zircons with an average age of 2690-2680. Ma. Thick (up to 2. km) dolerite bodies, such as the Golden Mile Dolerite, intrude the upper parts of the Early Black Flag Group at about 2680. Ma. Incipient development of large granite domes during Cycle One created extensional basins predominantly near their southeastern and northwestern margins (e.g., St Ives, Wallaby, Kanowna Belle and Agnew), into which the Early Black Flag Group and overlying coarse mafic conglomerate facies of the Late Black Flag Group were deposited. The clast compositions and detrital-zircon ages of the late Black Flag Group detritus match closely the nearby and/or stratigraphically underlying successions, thus suggesting relatively local provenance. Cycle Two involved a similar progression to that observed in Cycle One, but the age and composition of the detritus were notably different. Deposition of rapidly reworked quartz-rich pyroclastic deposits dominated by a single detrital-zircon age population of 2670-2660. Ma heralded the beginning of Cycle Two. These coarse-grained quartz-rich units, are name here the Early Merougil Group. The mean ages of the detrital zircons from the Early Merougil Group match closely the age of the peak in high-Ca (quartz-rich) granite magmatism in the Yilgarn Craton and thus probably represent the surface expression of the same event. Successions of the Late Merougil Group are dominated by coarse felsic conglomerate with abundant volcanic quartz. Although the detrital zircons in these successions have a broad spread of age, the principal sub-populations have ages of about 2665. Ma and thus match closely those of the Early Merougil Group. These successions occur most commonly at the northwestern and southeastern margins of the granite batholiths and thus are interpreted to represent resedimented units dominted by the stratigraphically underlying packages of the Early Merougil Group. The Kurrawang Group is the youngest sedimentary units identified in this study and is dominated by polymictic conglomerate with clasts of banded iron formation (BIF), granite and quartzite near the base and quartz-rich sandstone units containing detrital zircons aged up to 3500. Ma near the top. These units record provenance from deeper and/or more-distal sources. We suggest here that the principal driver for the major episodes of volcanism, sedimentation and deformation associated with basin development was the progressive emplacement of large granite batholiths. This interpretation has important implication for palaeogeographic and palaeotectonic evolution of all late-Archean terranes around the world. © 2010.
AUTHOR KEYWORDS: Archean;  Detrital zircons;  Provenance;  Tectonics;  U-Pb geochronology;  Volcaniclastic sediments;  Yilgarn Craton
DOCUMENT TYPE: Article
SOURCE: Scopus

Blewett, R.S.a , Squire, R.b , Miller, J.M.c , Henson, P.A.a , Champion, D.C.a 
Architecture and geodynamic evolution of the St Ives Goldfield, eastern Yilgarn Craton, Western Australia
(2010) Precambrian Research, 183 (2), pp. 275-291. Cited 9 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78449291132&partnerID=40&md5=a9d2fb7d0801937d4102d246437d2b2f
AFFILIATIONS: Geoscience Australia, Box 378, Canberra, ACT 2601, Australia; 
SChool of Geosciences, Monash University, Clayton, VIC 3800, Australia; 
Centre for Exploration Targeting, University of Western Australia, Crawley, Perth, Australia
ABSTRACT: A new structural evolution consisting of both extensional and contractional events has been defined for the St Ives Goldfield in the south-central Kalgoorlie Terrane of the eastern Yilgarn Craton in Western Australia. These events shaped the development of the fault architecture, which controlled the location of the regional anticlines, the magmatic centres, and the deposition of the Archaean greenstone successions. The fundamental grain of the St Ives Goldfield is north-northwest-trending. This trend is marked by faults which developed during D1 extension, which was oriented east-northeast-west-southwest. Across these faults we map major stratigraphic changes in the thickness and composition of units, especially of the previously undivided Black Flag Group volcaniclastic rocks. The centre of the St Ives Goldfield is dominated by the Kambalda Anticline. This north-northwest-trending regional fold was likely established early during the D1 extensional history, and was fully established during subsequent east-northeast-oriented D2 contraction. The regional anticline is an important architectural element because (1) magmatism and gold mineralising fluids were focussed into this domed region, and (2) deformation was partitioned across the limbs and crest of this structure. The D3 event involved regional uplift and extension, resulting in the formation of late basins (Merougil Conglomerate locally) and the emplacement of granitoids sourced from a metasomatised mantle wedge (Mafic-type porphyries). The most significant gold event in terms of endowment occurred during D4b sinistral strike-slip shearing and associated thrusting (e.g., Tramways and Republican thrusts). These thrusts were previously interpreted as the first contractional structures to deform the area ('D1'), but are here reinterpreted as relatively late (D4b). In this D4b event, the north-northwest-trending faults underwent sinistral strike-slip shearing and were linked across the Kambalda Anticline by accommodation structures represented by generally east- to east-northeast-trending thrusts. Reactivation of D1 transfer structures may have influenced the location of these later accommodation structures. Late-stage mineralisation during D5 was the result of dextral strike-slip brittle shearing. © 2010.
AUTHOR KEYWORDS: Archaean tectonics;  Eastern Yilgarn Craton;  Orogenic gold;  St Ives Goldfield
DOCUMENT TYPE: Article
SOURCE: Scopus

Edwards, B.R.a , Russell, J.K.b , Simpson, K.c 
Volcanology and petrology of Mathews Tuya, northern British Columbia, Canada: glaciovolcanic constraints on interpretations of the 0.730 Ma Cordilleran paleoclimate
(2010) Bulletin of Volcanology, pp. 1-18. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78049504988&partnerID=40&md5=2965c6b4e0c698a9b3313ed3de714b83
AFFILIATIONS: Department of Earth Sciences, Dickinson College, Carlisle, 17013, United States; 
Volcanology and Petrology Laboratory, Earth and Ocean Sciences, University of British Columbia, Vancouver, Canada; 
Geoscience BC, #440-890 West Pender Street, Vancouver, V6C 1J9, Canada
ABSTRACT: Petrological, volcanological and geochronological data collected at Mathews Tuya together provide constraints on paleoclimate conditions during formation of the edifice. The basaltic tuya was produced via Pleistocene glaciovolcanism in northern British Columbia, Canada, and is located within the Tuya volcanic field (59.195°N/130.434°W), which is part of the northern Cordilleran volcanic province (NCVP). The edifice comprises a variety of lithofacies, including columnar-jointed lava, pillow lava, massive dikes, and volcaniclastic rocks. Collectively these deposits record the transition from an explosive subaqueous to an effusive subaerial eruption environment dominated by Pleistocene ice. As is typical for tuyas, the volcaniclastic facies record multiple fragmentation processes including explosive, quench and mechanical fragmentation. All samples from Mathews Tuya are olivine-plagioclase porphyritic alkali olivine basalts. They are mineralogically and geochemically similar to nearby glaciovolcanic centers from the southeastern part of the Tuya volcanic field (e.g., Ash Mountain, South Tuya, Tuya Butte) as well as the dominant NCVP rock type. Crystallization scenarios calculated with MELTS account for variations between whole rock and glass compositions via low pressure fractionation. The presence of olivine microphenocrysts and the absence of pyroxene phenocrysts constrain initial crystallization pressures to less than 0.6 GPa. The eruption of Mathews Tuya occurred between 0.718 ± 0.054 Ma and 0.742 ± 0.081 Ma based on 40Ar/39Ar geochronology (weighted mean age of 0.730 Ma). The age determinations provide the first firm documentation for large (&gt;700 m thick), pre-Fraser/Wisconsin glaciers in north-central British Columbia ~0.730 Ma, and correlate in age with glaciovolcanic deposits in Russia (e.g., Komatsu et al. Geomorph 88: 352-366, 2007) and with marine isotopic evidence for large global ice volumes ~0.730 Ma. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: AOB;  Cordilleran;  Glaciation;  Mathews;  NCVP;  Pleistocene;  Tuya
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Acharyya, S.K.a , Gupta, A.b , Orihashi, Y.c 
Neoarchean-Paleoproterozoic stratigraphy of the Dhanjori basin, Singhbhum Craton, Eastern India: And recording of a few U-Pb zircon dates from its basal part
(2010) Journal of Asian Earth Sciences, 39 (6), pp. 527-536. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77957589531&partnerID=40&md5=0a23befa04d023d785ab57bad7efec38
AFFILIATIONS: Department of Geological Sciences, Jadavpur University, Kolkata 700 032, India; 
BB 45/3, Salt Lake, Kolkata 700 064, India; 
Earthquake Research Institute, University of Tokyo, Bunkyo, Tokyo113-0032, Japan
ABSTRACT: The stratigraphy of the Dhanjori basin placed at the northeastern margin of the Paleo-Mesoarchean Singhbhum Craton has been revised. A mainly quartz-pebble conglomerate (QPC) and volcani-clastics bearing unit at the base of the Dhanjori basin and intruded by the Mayurbhanj Granite, has been named Phuljhari Formation. The Dhanjori volcani-sedimentary sequence with quartzite-polymictic conglomerate at its base, disconformably overlies the Phuljhari Formation and non-conformaby over the Mayurbhanj Granite. The Dhanjori Group is inferred to broadly range in age from 2.6-2.1. Ga. Detrital zircons from QPC belonging to the Phuljhari Formation have yielded oldest chemical ages of 3.09-3.04. Ga thus fixing the upper age limit of the formation. The 3.09. Ga old zircons recovered earlier from the Mayurbhanj Granite, which is intrusive into the relatively younger Phuljhari Fm., therefore appears to be xenocrystic in nature. A fine grained variety of the Mayubhanj Granite, close to its intrusive contact with the Phuljhari Fm., was sampled during the present study. It has recorded strong impress of acid magmatic event around 1.0-0.8. Ga by its lower intercept and an upper intercept age of ∼2.8. Ga. The latter might record the inherited age of protolith to the Mayurbhanj Granite and correspond to widespread granite magmatic activity affecting the margin of the Singhbhum Craton. Signature of 1.0-0.08. Ga old thermal perturbation also affected lower parts of the Dhanjori basin and the Singhbhum Shear Zone. Detrital Au-U bearing QPC in the Phuljhari Formation represent Neoarchean sedimentation at the margin of the peneplained craton. The Dhanjhori Group comprising mafic-ultramafic volcanics and siliciclastics was hosted in rift induced intracratonic basin around Neoarchean-Palaeoproterozoic threshold. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Dhanjori basin stratigraphy;  Mayurbhanj Granite;  Neoarchaean QPC-bearing Phuljhari Formation;  Singhbhum Craton;  U-Pb zircon dates
DOCUMENT TYPE: Article
SOURCE: Scopus

Kaneda, K.a , Kodaira, S.b , Nishizawa, A.a , Morishita, T.a , Takahashi, N.b 
Structural evolution of preexisting oceanic crust through intraplate igneous activities in the Marcus-Wake seamount chain
(2010) Geochemistry, Geophysics, Geosystems, 11 (10), art. no. Q10014, . 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78049394823&partnerID=40&md5=df9a24aa51c8024e0640d5715c1588ab
AFFILIATIONS: Hydrographic and Oceanographic Department, Japan Coast Guard, Tsukiji 5-3-1, Chuo-ku, Tokyo 104-0045, Japan; 
Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama 236-0001, Japan
ABSTRACT: Multichannel seismic reflection studies and seismic refraction surveys with ocean bottom seismographs in the Marcus-Wake seamount chain in the northwestern Pacific Ocean reveal P wave velocity structures of hot spot-origin seamounts and adjacent oceanic crust. Inside the seamounts are central high-velocity (>6.5 km/s) structures extending nearly to the top that may indicate intrusive cores. Thick sediment layers (up to 4 km) with P wave velocities of 4-5 km/s have accumulated on seafloor that predates seamount formation. Downward crustal thickening of up to 2 km was documented beneath a large seamount cluster, but thickening was not confirmed below a small seamount cluster. Volume ratios of an intrusive core to a seamount body are 15-20%, indicating that most of the supplied magma was consumed in forming the thick sedimentary and volcaniclastic layer constituting the seamount flanks. Underplating and downward crustal thickening may tend to occur when second or later intrusive cores are formed in a seamount. P wave velocities in the lowest crust and in the uppermost mantle below the seamount chain are 0.1-0.2 km/s higher and 0.3-0.5 km/s lower, respectively, than velocities below oceanic crust. We explain this difference as a result of sill-like intrusion of magma into the lower crust and uppermost mantle. Reflected waves observed at offsets >200 km are from mantle reflectors at depths of 30-45 km and 55-70 km. The shallower reflectors may indicate structures formed by intraplate igneous activities, and the deeper reflectors may correspond to the lithosphere-asthenosphere boundary.
AUTHOR KEYWORDS: crustal structure;  hot spot;  seamount;  seismic experiment
DOCUMENT TYPE: Article
SOURCE: Scopus

Bisson, M.a , Sulpizio, R.b , Zanchetta, G.c , Demi, F.c , Santacroce, R.c 
Rapid terrain-based mapping of some volcaniclastic flow hazard using Gis-based automated methods: A case study from southern Campania, Italy
(2010) Natural Hazards, 55 (2), pp. 371-387. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78049321836&partnerID=40&md5=bd6549ea949fe86b5a26742ea0508e23
AFFILIATIONS: Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, via della Faggiola 32, 56126 Pisa, Italy; 
CIRISIVU, c/o Dipartimento Geomineralogico, Università di Bari, via Orabona 4, 70125 Bari, Italy; 
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria, 53, 56126 Pisa, Italy
ABSTRACT: Destructive volcaniclastic flows are among the most recurrent and dangerous natural phenomena in volcanic areas. They can originate not only during or shortly after an eruption (syn-eruptive) but also during a period of volcanic quiescence (inter-eruptive), when heavy and/or persistent rains remobilize loose pyroclastic deposits. The area in Italy most prone to such flows is that of the Apennine Mountains bordering the southern Campania Plain. These steep slopes are covered by pyroclastic material of variable thickness (a few cm to several m) derived from the explosive activity of the Somma-Vesuvius and Campi Flegrei volcanoes a few tens of kilometers to the west. The largest and most recent devastating event occurred on May 5, 1998, causing the death of more than 150 people and considerable damage to villages at the foot of the Apennine Mountains. This tragic event was only the most recent of a number of volcaniclastic flows affecting the area in both historical and prehistoric times. Historical accounts report that more than 500 events have occurred in the last five centuries and that more than half of these occurred in the last 100 years, causing hundreds of deaths. In order to improve volcaniclastic flow hazard zonation and risk mitigation in the study area, we produced a zonation map that identifies the drainage basins potentially prone to disruption. This map was obtained by combining morphological characteristics (concavity and basin shape factor) and the mean slope distribution of drainage basins derived from a digital elevation model with a 10-m resolution. These parameters allowed for the classification of 1,069 drainage basins, which have been grouped into four different classes of proneness to disruption: low, moderate, high and very high. The map compiled in a GIS environment, as well as the linked database, can be rapidly queried. © 2010 Springer Science+Business Media B.V.
AUTHOR KEYWORDS: GIS;  Slope instability;  Southern Campania Plain;  Vesuvian area;  Volcaniclastic flow hazard
DOCUMENT TYPE: Article
SOURCE: Scopus

Gurioli, L.a  b  c , Sulpizio, R.d , Cioni, R.e , Sbrana, A.f , Santacroce, R.f , Luperini, W.f , Andronico, D.g 
Pyroclastic flow hazard assessment at Somma-Vesuvius based on the geological record
(2010) Bulletin of Volcanology, 72 (9), pp. 1021-1038. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78249284588&partnerID=40&md5=f7fe1df316ea205a33e75b87a0602bc2
AFFILIATIONS: Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, 63000 Clermont-Ferrand, France; 
CNRS, UMR 6524, LMV, 63038 Clermont-Ferrand, France; 
IRD, R 163, LMV, 63038 Clermont-Ferrand, France; 
CIRISIVU, c/o Dipartimento Geomineralogico, via Orabona, 4, 70125 Bari, Italy; 
Dipartimento di Scienze della Terra, Via Trentino 51, 09127 Cagliari, Italy; 
Dipartimento di Scienze della Terra, Via S. Maria 53, 56126 Pisa, Italy; 
INGV sezione di Catania Piazza Roma, 2, 95123 Catania, Italy
ABSTRACT: During the past 22 ka of activity at Somma-Vesuvius, catastrophic pyroclastic density currents (PDCs) have been generated repeatedly. Examples are those that destroyed the towns of Pompeii and Ercolano in AD 79, as well as Torre del Greco and several circum-Vesuvian villages in AD 1631. Using new field data and data available from the literature, we delineate the area impacted by PDCs at Somma-Vesuvius to improve the related hazard assessment. We mainly focus on the dispersal, thickness, and extent of the PDC deposits generated during seven plinian and sub-plinian eruptions, namely, the Pomici di Base, Greenish Pumice, Pomici di Mercato, Pomici di Avellino, Pompeii Pumice, AD 472 Pollena, and AD 1631 eruptions. We present maps of the total thickness of the PDC deposits for each eruption. Five out of seven eruptions dispersed PDCs radially, sometimes showing a preferred direction controlled by the position of the vent and the paleotopography. Only the PDCs from AD 1631 eruption were influenced by the presence of the Mt Somma caldera wall which stopped their advance in a northerly direction. Most PDC deposits are located downslope of the pronounced break-in slope that marks the base of the Somma-Vesuvius cone. PDCs from the Pomici di Avellino and Pompeii Pumice eruptions have the most dispersed deposits (extending more than 20 km from the inferred vent). These deposits are relatively thin, normally graded, and stratified. In contrast, thick, massive, lithic-rich deposits are only dispersed within 7 to 8 km of the vent. Isopach maps and the deposit features reveal that PDC dispersal was strongly controlled by the intensity of the eruption (in terms of magma discharge rate), the position of the vent area with respect to the Mt Somma caldera wall, and the pre-existing topography. Facies characteristics of the PDC deposits appear to correlate with dispersal; the stratified facies are consistently dispersed more widely than the massive facies. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Facies;  Hazard assessment;  Mt Somma;  Pyroclastic density currents;  Pyroclastic flow
DOCUMENT TYPE: Article
SOURCE: Scopus

Folch, A.a , Sulpizio, R.b 
Evaluating long-range volcanic ash hazard using supercomputing facilities: Application to Somma-Vesuvius (Italy), and consequences for civil aviation over the Central Mediterranean Area
(2010) Bulletin of Volcanology, 72 (9), pp. 1039-1059. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78149496979&partnerID=40&md5=4c505addc94cf40da1c9635b8dfdfa58
AFFILIATIONS: Barcelona Supercomputing Center, Centro Nacional de Supercomputación, c/Jordi Girona 29, 08034 Barcelona, Spain; 
CIRISIVU, c/o Dipartimento Geomineralogico, Via Orabona, 4, 70125 Bari, Italy
ABSTRACT: Volcanic ash causes multiple hazards. One hazard of increasing importance is the threat posed to civil aviation, which occurs over proximal to long-range distances. Ash fallout disrupts airport operations, while the presence of airborne ash at low altitudes near airports affects visibility and the safety of landing and take-off operations. Low concentrations of ash at airplane cruise levels are sufficient to force re-routing of in-flight aircrafts. Volcanic fallout deposits spanning large distances have been recognized from the Somma-Vesuvius volcano for several Holocene explosive eruptions. Here we develop hazard and isochron maps for distal ash fallout from the Somma-Vesuvius, as well as hazard maps for critical ash concentrations at relevant flight levels. Maps are computed by coupling a meteorological model with a fully numeric tephra dispersal model that can account for ash aggregation processes, which are relevant to the dispersion dynamics of fine ash. The simulations were carried out using supercomputing facilities, spanning on entire meteorological year that is statistically representative of the local meteorology during the last few decades. Seasonal influences are also analyzed. The eruptive scenario is based on a Subplinian I-type eruption, which is within the range of the maximum expected event for this volcano. Results allow us to quantify the impact that an event of this magnitude and intensity would have on the main airports and aerial corridors of the Central Mediterranean Area. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Aerial navigation safety;  Ash fallout;  Hazard maps;  Somma-Vesuvius;  Supercomputer
DOCUMENT TYPE: Article
SOURCE: Scopus

Vasiliev, I.a , de Leeuw, A.a , Filipescu, S.b , Krijgsman, W.a , Kuiper, K.c , Stoica, M.d , Briceag, A.e 
The age of the Sarmatian-Pannonian transition in the Transylvanian Basin (Central Paratethys)
(2010) Palaeogeography, Palaeoclimatology, Palaeoecology, 297 (1), pp. 54-69. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956873472&partnerID=40&md5=d11595d3091bd6459b9b871da82c240c
AFFILIATIONS: Paleomagnetic Laboratory 'Fort Hoofddijk', Budapestlaan 17, 3584 CD, Utrecht, Netherlands; 
Department of Geology, 'Babeş-Bolyai' University, Kogǎlniceanu St. 1, 400084 Cluj-Napoca, Romania; 
Department of Isotope Geochemistry, Faculty of Earth and Life Sciences, Vrije University, De Boelelaan 1085, 1081 HV, Amsterdam, Netherlands; 
Department of Palaeontology, Faculty of Geology and Geophysics, University of Bucharest, Bǎlcescu Bd. 1, Bucharest, 010041, Romania; 
National Institute of Marine Geology and Geoecology, GeoEcoMar, Dimitrie Onciul Street 23-25, Bucharest, 70318, Romania
ABSTRACT: A marked paleoenvironmental change took place at the beginning of the late Miocene in the Central Paratethys, with dominantly marine Sarmatian successions grading rapidly into mainly brackish Pannonian deposits. A long and excellently exposed section comprising the Sarmatian-Pannonian transition has been investigated at Oarba de Mure? in the Transylvanian basin (Romania). In this paper, we focus on both radiometric and magnetostratigraphic dating to provide a chronology for the Sarmatian-Pannonian transition in Transylvania. Two volcaniclastic layers, located approximately 40m below the Sarmatian-Pannonian transition, yield excellent 40Ar/39Ar ages. The weighted mean plateau age for biotite and sanidine separates provided isotopic ages of 11.62±0.12Ma and 11.65±0.13Ma. This implies deposition during the magnetic chron C5r.2r, which is in agreement with the magnetostratigraphic results of the Oarba de Mure? composite section. Rock magnetic analyses indicate greigite as the main magnetic carrier, with characteristics very similar to the magnetosomal greigite found in the Carpathian foredeep. The newly obtained chronology at Oarba de Mure? constrains the age of the Sarmatian-Pannonian transition in the Transylvanian basin to 11.3±0.1Ma, slightly younger than the 11.61Ma postulated in the Styrian and Vienna Basins. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: 40Ar/39Ar dating;  Central Paratethys;  Magnetostratigraphy;  Pannonian;  Sarmatian
DOCUMENT TYPE: Article
SOURCE: Scopus

Villani, F., Pierdominici, S.
Late Quaternary tectonics of the Vallo di Diano basin (southern Apennines, Italy)
(2010) Quaternary Science Reviews, 29 (23-24), pp. 3167-3183 begin_of_the_skype_highlighting              3167-3183      end_of_the_skype_highlighting. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77957604364&partnerID=40&md5=ae5f33bbf28846754a723e884f63e3a5
AFFILIATIONS: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy
ABSTRACT: We discuss new data concerning the late Quaternary tectonics of the Vallo di Diano basin, the largest intramontane depression in the southern Apennines chain (Italy). The southern Apennines axis is currently subject to NE-SW extension. Here, active NW-trending normal faults are associated with strong earthquakes (M > 6), with average recurrence times >1 ka. The Vallo di Diano basin is a half-graben bounded by an extensional fault system VDFS (Vallo di Diano Fault System), featuring three major NW-trending, SW-dipping, ∼15-17 km long fault segments. Holocene faulting and possible historical seismicity have been documented only for the northern fault segment. No major historical earthquakes can be associated with the other fault segments, and the recent sedimentary and structural evolution of the basin is still poorly constrained. As a consequence, its seismogenetic potential has probably been underestimated. We found evidence of late Pleistocene-Holocene faulting in the relay zone of the central and southern fault segments bordering the basin. Here, late Pleistocene volcaniclastic layers at the apex of an alluvial fan are affected by normal displacements on the order of ∼1 m. Additionally, in the same area we recognized a previously unreported, 9 km long and 0.5-1.4 km wide set of scarplets (ranging in height between ∼1 m and 2.5 m) affecting late Pleistocene-late Holocene alluvial fans. The last deformation is younger than 3 ka BP. Due to the geometric arrangement of these scarplets and the long-term displacement along the Vallo di Diano Fault System, we hypothesize that the central and southern fault segments belong to a ∼32 km long hard-linked system, capable of generating Mw > 6.5 earthquakes. The Vallo di Diano basin is thus bounded to the east for its entire length (∼45 km) by an active segmented extensional fault system. Therefore it has to be considered one of the major seismogenic sources in southern Italy. © 2010 Elsevier Ltd.
DOCUMENT TYPE: Article
SOURCE: Scopus

Kenedi, C.L.a  b , Sparks, R.S.J.c , Malin, P.a  b , Voight, B.d , Dean, S.e , Minshull, T.e , Paulatto, M.e , Peirce, C.f , Shalev, E.a  b 
Contrasts in morphology and deformation offshore Montserrat: New insights from the SEA-CALIPSO marine cruise data
(2010) Geophysical Research Letters, 37 (19), art. no. L00E25, . 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77958063113&partnerID=40&md5=39c97fc3a1d26ab430d4a8843a825eca
AFFILIATIONS: Earth and Ocean Sciences, Duke University, Durham, NC, United States; 
Institute of Earth Science and Engineering, University of Auckland, Auckland, New Zealand; 
Department of Earth Sciences, University of Bristol, Bristol, United Kingdom; 
Department of Geosciences, Pennsylvania State University, University Park, PA, United States; 
National Oceanography Centre, University of Southampton, Southampton, United Kingdom; 
Department of Earth Sciences, Durham University, Durham, NC, United States
ABSTRACT: During the December 2007, SEA-CALIPSO experiment we collected seismic reflection profiles offshore of Montserrat. Off the east coast, we imaged deep fans of volcaniclastic debris from three volcanoes progressively active from ∼2 Ma to present. Near-shelf sedimentation rates of 8-9 cm/ka are approximated following cessation of local volcanic activity. The fans were deposited on sediments with apparent dips towards the ESE-trending Montserrat-Havers fault system (MHFS) in southern Montserrat. The MHFS encloses the Soufrire Hills Volcano, has elevated crustal blocks at Roche's Bluff, St. Georges Hill, and Garibaldi Hill, and extends off the west coast. Off the west coast, the N-dip of two faults supports a N-dip interpretation for a major component of MHFS, the Belham Valley fault. We propose that local deformation is affected by stress redistributions consistent with a right-stepping, sinistral en-echelon fault system, but the interplay of transtension and magmatism has resulted in complex and evolving stress regimes. Copyright 2010 by the American Geophysical Union.
DOCUMENT TYPE: Article
SOURCE: Scopus

Aslan, Z.
U-Pb zircon SHRIMP age, geochemical and petrographical characteristics of tuffs within calc-alkaline Eocene volcanics around Gümüşhane (NE Turkey), Eastern Pontides
(2010) Neues Jahrbuch fur Mineralogie, Abhandlungen, 187 (3), pp. 329-346. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78649542793&partnerID=40&md5=b27d8511d448fdac213adeb7a9c35215
AFFILIATIONS: Department of Geological Engineering, Engineering and Architecture Faculty, Bahkesir University, 10145 Bahkesir, Turkey
ABSTRACT: Eocene units are widespread in the Eastern Pontides, unconformably overlying Upper Cretaceous volcanoclastic and sedimentary rocks. The Eocene units consist mainly of lava flows and lesser tuffs and sediments. In the study area, the Gümüşhane region, tuffs are interbedded with lava flows, over an area of -15 km2. Petrographically, the tuffs can be classified into vitric tuff, crystal tuff, lapilli tuff, and locally silicified tuff. The tuffs, which are cut by dolerite dykes, contain plagioclase (An 28-30), amphibole, glass shards, and minor pyroxene, K-feldspar, opaque oxides, and zircon, as well as secondary clay, sericite, calcite, chlorite, and devitrified glass. The U-Pb zircon SHRIMP age from the tuff is 45.8 ± 1.2 Ma, which is regarded as the crystallization age. U and Th concentrations within zircon grains vary from 343 to 744 ppm and from 203 to 605 ppm, respectively, and Th/U ratios range from 0.59 to 1.27, indicating precipitation from a melt. Geochemically, the tuffs have calc-alkaline volcanic-arc characteristics. The trace element compositions are indicative of subduction-zone volcanism. The tuffs have high large ion lithophile elements (LILEs) contents and low high field strength elements (HFSEs) contents compared to N-type Mid-Ocean Ridge Basalt (MORB). Chondritenormalized rare earth element (REE) patterns are concave upwards indicating significant fractional crystallization during evolution of the melt, with (La/Lu)CN = 1.28-13.35. Moderately negative (Eu/Eu*)CN ratios are in the range 0.45-1.07, reflecting plagioclase fractionation. From the trace element signature it is concluded that the parental melt was derived from an enriched upper mantle and formed in an intra-arc basin. © 2010 E. Schweizerbart'sche Verlagsbuchhandlung. Stuttagrt, Germany.
AUTHOR KEYWORDS: Calc-alkaline;  Eastern pontides;  Geochemistry;  Gümüşhane;  Tertiary volcanism;  Tuff;  U-Pb zircon age
DOCUMENT TYPE: Article
SOURCE: Scopus

Bayona, G.a  b , Jiménez, G.a , Silva, C.a  b , Cardona, A.a  b , Montes, C.a  b , Roncancio, J.c , Cordani, U.d 
Paleomagnetic data and K-Ar ages from Mesozoic units of the Santa Marta massif: A preliminary interpretation for block rotation and translations
(2010) Journal of South American Earth Sciences, 29 (4), pp. 817-831. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77958184698&partnerID=40&md5=94106c1828f1b14ed1bd0efd23c4de08
AFFILIATIONS: Corporación Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia; 
Smithsonian Tropical Research Institute, Ancon, Panama; 
Geosearch Ltda, Bogotá, Colombia; 
Department of Geosciences, University of São Paulo, São Paulo, Brazil
ABSTRACT: We report 6. K-Ar ages and paleomagnetic data from 28 sites collected in Jurassic, Lower Cretaceous and Paleocene rocks of the Santa Marta massif, to test previous hypothesis of rotations and translations of this massif, whose rock assemblage differs from other basement-cored ranges adjacent to the Guyana margin. Three magnetic components were identified in this study. A first component has a direction parallel to the present magnetic field and was uncovered in all units (D= 352, I= 25.6, k= 57.35, a95 = 5.3, N= 12). A second component was isolated in Cretaceous limestone and Jurassic volcaniclastic rocks (D= 8.8, I= 8.3, k= 24.71, a95 = 13.7, N= 6), and it was interpreted as of Early Cretaceous age. In Jurassic sites with this component, Early Cretaceous K-Ar ages obtained from this and previous studies are interpreted as reset ages. The third component was uncovered in eight sites of Jurassic volcaniclastic rocks, and its direction indicates negative shallow to moderate inclinations and northeastward declinations. K-Ar ages in these sites are of Early (196.5 ± 4.9. Ma) to early Late Jurassic age (156.6 ± 8.9. Ma). Due to local structural complexity and too few Cretaceous outcrops to perform a reliable unconformity test, we only used two sites with (1) K-Ar ages, (2) less structural complexity, and (3) reliable structural data for Jurassic and Cretaceous rocks. The mean direction of the Jurassic component is (D = 20.4, I = -18.2, k = 46.9, a95 = 5.1, n = 18 specimens from two sites). These paleomagnetic data support previous models of northward along-margin translations of Grenvillian-cored massifs. Additionally, clockwise vertical-axis rotation of this massif, with respect to the stable craton, is also documented; the sense of rotation is similar to that proposed for the Perija Range and other ranges of the southern Caribbean margin. More data is needed to confirm the magnitudes of rotations and translations. © 2009 Elsevier Ltd.
AUTHOR KEYWORDS: Caribbean tectonics;  Jurassic paleogeography;  Santa Marta massif;  Terrane translation;  Vertical-axis rotation
DOCUMENT TYPE: Article
SOURCE: Scopus

Romans, B.W.a , Fildani, A.b , Graham, S.A.a , Hubbard, S.M.c , Covault, J.A.a 
Importance of predecessor basin history on sedimentary fill of a retroarc foreland basin: provenance analysis of the Cretaceous Magallanes basin, Chile (50-52°S)
(2010) Basin Research, 22 (5), pp. 640-658. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953818522&partnerID=40&md5=dc8f3ed794356d31d4fded9c1832f80f
AFFILIATIONS: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, United States; 
Chevron Energy Technology Company, Clastic Stratigraphy R and D, San Ramon, CA, United States; 
Department of Geoscience, University of Calgary, Calgary, AB, Canada
ABSTRACT: An integrated provenance analysis of the Upper Cretaceous Magallanes retroarc foreland basin of southern Chile (50°30'-52°S) provides new constraints on source area evolution, regional patterns of sediment dispersal and depositional age. Over 450 new single-grain detrital-zircon U-Pb ages, which are integrated with sandstone petrographic and mudstone geochemical data, provide a comprehensive detrital record of the northern Magallanes foreland basin-filling succession (>4000-m-thick). Prominent peaks in detrital-zircon age distribution among the Punta Barrosa, Cerro Toro, Tres Pasos and Dorotea Formations indicate that the incorporation and exhumation of Upper Jurassic igneous rocks (ca. 147-155 Ma) into the Andean fold-thrust belt was established in the Santonian (ca. 85 Ma) and was a significant source of detritus to the basin by the Maastrichtian (ca. 70 Ma). Sandstone compositional trends indicate an increase in volcanic and volcaniclastic grains upward through the basin fill corroborating the interpretation of an unroofing sequence. Detrital-zircon ages indicate that the Magallanes foredeep received young arc-derived detritus throughout its ca. 20 m.y. filling history, constraining the timing of basin-filling phases previously based only on biostratigraphy. Additionally, spatial patterns of detrital-zircon ages in the Tres Pasos and Dorotea Formations support interpretations that they are genetically linked depositional systems, thus demonstrating the utility of provenance indicators for evaluating stratigraphic relationships of diachronous lithostratigraphic units. This integrated provenance dataset highlights how the sedimentary fill of the Magallanes basin is unique among other retroarc foreland basins and from the well-studied Andean foreland basins farther north, which is attributed to nature of the predecessor rift and backarc basin. © 2009 The Authors. Journal Compilation © Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.
DOCUMENT TYPE: Article
SOURCE: Scopus

Gomez, C.a , Janin, M.d  e , Lavigne, F.c , Gertisser, R.f , Charbonnier, S.f , Lahitte, P.d , Hadmoko, S.R.c  g , Fort, M.b , Wassmer, P.b  h , Degroot, V.i , Murwanto, H.j 
Borobudur, a basin under volcanic influence: 361,000 years BP to present
(2010) Journal of Volcanology and Geothermal Research, 196 (3-4), pp. 245-264. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956772792&partnerID=40&md5=5125f9a52fa6eb32b9f35aa4cb1a13f2
AFFILIATIONS: University of Canterbury, College of Sciences, Department of Geography, Private Bag 4800, Christchurch 8140, New Zealand; 
University Paris 7 Denis Diderot, Lab. PRODIG, CNRS UMR8586, Paris, France; 
University Paris 1 Pantheon-Sorbonne, Laboratoire LGP, CNRS UMR8591, Paris, France; 
University Paris Sud XI, Lab. De Géochronologie, Multi-techniques, UMR 8148 IDES, Orsay, France; 
University Bretagne Occidentale, UMR 6538 Domaines Océaniques, Institut Universitaire Européen de la Mer, Plouzane, France; 
Keele University, School of Physical and Geographical Sciences, Earth Sciences and Geography, Keele, Staffordshire, ST5 5BG, United Kingdom; 
University Gadja Madah, Dept. of Physical Geography, Yogyakarta, Indonesia; 
University Louis Pasteur, Strasbourg, France; 
Rijksmuseum voor Volkenkunde, Insular Southeast Asian Res., Leiden, Netherlands; 
University UPN, Dept. of Geology, Yogyakarta, Indonesia
ABSTRACT: Borobudur basin is located in Central Java (Indonesia), 30 km to the North of Yogyakarta City. The basin is famous for its UNESCO world heritage temple and for one of the world's most active volcanoes, Merapi, located to the East of Borobudur basin. Merapi is one of the three andesitic volcanoes that surround the basin: Merapi, Merbabu and Sumbing volcanoes. Therefore, volcanic activity has strongly influenced the evolution of Borobudur basin. The object of this contribution is to present the evolution of Borobudur basin over the last 161,000. years in the light of volcanic influence. The methodology and tools developed for this research span over different areas of expertise, from geochemistry, geology and geomorphology to remote sensing, GIS and archeology.Results highlight the following points:. 1.Two major volcanic events deposited volcaniclastic materials up to tens of meters thick ~119,000years BP and ~31,000years BP. in the Southern part of the Borobudur basin. The second volcanic event could correspond to the collapse of the older Ancient Merapi (Camus et al., 2000) or Proto-Merapi Stage (Newhall et al., 2000).2.There is no trace in the Borobudur basin of a large debris avalanche <31,000 BP, indicating that the young debris avalanche inferred in the literature for Merapi Volcano was either too small to reach 20 km from the actual summit of Merapi; or, despite the orientation of the avalanche caldera rim on Merapi Volcano, the debris avalanche was deposited more towards the South, completely eroded or covered by younger deposits.3.There are several generations of paleolakes in the Borobudur basin. The latest one has shrunk until historical times, corroborating the theory of Newhall et al. (2000) and Murwanto et al. (2004) that Borobudur Temple was standing by a water body. Most of these paleolakes were impounded following volcanic events. Paleolakes most probably originated from the blockage of the hydrographic network by volcanic material.4.Borobudur temple was never buried under volcanic material during historic times. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Borobudur basin;  Geochemistry;  Geomorphology;  Indonesia;  Java;  K/Ar Dating;  Merapi;  Paleolake;  Paleomagnetism;  Pyroclastic flows;  Quaternary;  Volcano
DOCUMENT TYPE: Article
SOURCE: Scopus

Pike, A.S.a , Scatena, F.N.a , Wohl, E.E.b 
Lithological and fluvial controls on the geomorphology of tropical montane stream channels in Puerto Rico
(2010) Earth Surface Processes and Landforms, 35 (12), pp. 1402-1417. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955830561&partnerID=40&md5=f5a4adf6beac00278bbba6f09aee3c96
AFFILIATIONS: University of Pennsylvania, Department of Earth and Environmental Science, 240 S. 33 rd Street, Hayden Hall, Philadelphia, PA 19104, United States; 
Colorado State University, Department of Geosciences, Warner College of Natural Resources, Room 330, Ft Collins CO 80523-1482, United States
ABSTRACT: An extensive survey and topographic analysis of five watersheds draining the Luquillo Mountains in north-eastern Puerto Rico was conducted to decouple the relative influences of lithologic and hydraulic forces in shaping the morphology of tropical montane stream channels. The Luquillo Mountains are a steep landscape composed of volcaniclastic and igneous rocks that exert a localized lithologic influence on the stream channels. However, the stream channels also experience strong hydraulic forcing due to high unit discharge in the humid rainforest environment. GIS-based topographic analysis was used to examine channel profiles, and survey data were used to analyze downstream changes in channel geometry, grain sizes, stream power, and shear stresses. Results indicate that the longitudinal profiles are generally well graded but have concavities that reflect the influence of multiple rock types and colluvial-alluvial transitions. Non-fluvial processes, such as landslides, deliver coarse boulder-sized sediment to the channels and may locally determine channel gradient and geometry. Median grain size is strongly related to drainage area and slope, and coarsens in the headwaters before fining in the downstream reaches; a pattern associated with a mid-basin transition between colluvial and fluvial processes. Downstream hydraulic geometry relationships between discharge, width and velocity (although not depth) are well developed for all watersheds. Stream power displays a mid-basin maximum in all basins, although the ratio of stream power to coarse grain size (indicative of hydraulic forcing) increases downstream. Excess dimensionless shear stress at bankfull flow wavers around the threshold for sediment mobility of the median grain size, and does not vary systematically with bankfull discharge; a common characteristic in self-forming 'threshold' alluvial channels. The results suggest that although there is apparent bedrock and lithologic control on local reach-scale channel morphology, strong fluvial forces acting over time have been sufficient to override boundary resistance and give rise to systematic basin-scale patterns. Copyright © 2010 John Wiley and Sons, Ltd.
AUTHOR KEYWORDS: Channel profiles;  Colluvial-fluvial processes;  Hydraulics;  Lithology;  Morphology;  Mountain streams
DOCUMENT TYPE: Article
SOURCE: Scopus

Westall, F.a , Foucher, F.a , Cavalazzi, B.a , de Vries, S.T.b , Nijman, W.b , Pearson, V.c , Watson, J.c , Verchovsky, A.c , Wright, I.c , Rouzaud, J.-N.d , Marchesini, D.e , Anne, S.f 
Volcaniclastic habitats for early life on Earth and Mars: A case study from ∼3.5 Ga-old rocks from the Pilbara, Australia
Planetary and Space Science, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956839856&partnerID=40&md5=3ac7fc0ff3c1d86a2b18726fa7d78718
AFFILIATIONS: Centre de Biophysique Moléculaire, CNRS-OSUC, Rue Charles Sadron, 45071 Orléans, France; 
Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands; 
Planetary and Space Sciences Research Institute (PSSRI), The Open University, Walton Hall, Milton Keynes K7 6AA, UK; 
Laboratoire de Géologie, Ecole Normale Supérieure, de Paris, 24, rue, Lhomond, 75231 Paris, Cedex 5, France; 
via Torino 10, 40139 Bologna, Italy; 
Department of Geological Sciences, University of Orléans, 45071 Orléans, Cedex 2, France
ABSTRACT: Within the context of present and future in situ missions to Mars to investigate its habitability and to search for traces of life, we studied the habitability and traces of past life in ∼3.5 Ga-old volcanic sands deposited in littoral environments an analogue to Noachian environments on Mars. The environmental conditions on Noachian Mars (4.1-3.7 Ga) and the Early Archaean (4.0-3.3 Ga) Earth were, in many respects, similar: presence of liquid water, dense CO2 atmosphere, availability of carbon and bio-essential elements, and availability of energy. For this reason, information contained in Early Archaean terrestrial rocks concerning habitable conditions (on a microbial scale) and traces of past life are of relevance in defining strategies to be used to identify past habitats and past life on Mars. One such example is the 3.446 Ga-old Kitty's Gap Chert in the Pilbara Craton, NW. Australia. This formation consists of volcanic sediments deposited in a coastal mudflat environment and is thus a relevant analogue for sediments deposited in shallow water environments on Noachian Mars. Two main types of habitat are represented, a volcanic (lithic) habitat and planar stabilized sediment surfaces in sunlit shallow waters. The sediments hosted small (&lt;1 μm in size) microorganisms that formed colonies on volcanic particle surfaces and in pore waters within the volcanic sediments, as well as biofilms on stabilised sediment surfaces. The microorganisms included coccoids, filaments and rare rod-shaped organisms associated with microbial polymer (EPS). The preserved microbial community was apparently dominated by chemotrophic organisms but some locally transported filaments and filamentous mat fragments indicate that possibly photosynthetic mats formed nearby. Both microorganisms and sediments were silicified during very early diagenesis. There are no macroscopic traces of fossilised life in these volcanic sediments and sophisticated instrumentation and specialized sample preparation techniques are required to establish the biogenicity and syngenicity of the traces of past life. The fact that the traces of life are cryptic, and the necessity of using sophisticated instrumentation, reinforces the challenges and difficulties of in situ robotic missions to identify past life on Mars. We therefore recommend the return of samples from Mars to Earth for a definitive search for traces of life. © 2010 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Early Archaean;  Mars;  Microfossils;  Pilbara;  Volcanic sediments
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Donoghue, E.a , Troll, V.R.b , Harris, C.c 
Fluid-rock interaction in the miocene, post-caldera, Tejeda Intrusive Complex, Gran Canaria (Canary Islands): Insights from mineralogy, and O- and H-isotope geochemistry
(2010) Journal of Petrology, 51 (10), art. no. egq052, pp. 2149-2176. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77957278325&partnerID=40&md5=b194915d636cf9b158e4d701ff9c0415
AFFILIATIONS: Department of Geology, University of Dublin, Trinity College, Dublin 2, Ireland; 
Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden; 
Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa
ABSTRACT: The intra-caldera volcaniclastic deposits of the Miocene Tejeda caldera on Gran Canaria host an ∼12 km diameter intrusive complex comprising a peralkaline, trachytic to phonolitic cone sheet swarm surrounding a central core of hypabyssal syenite stocks. Both intrusive rock types display textural and mineralogical features indicative of secondary fluid-rock interaction, including (1) deuteric mineral phases (e.g. aegirine, alkali-amphibole, analcime), (2) turbid alkali feldspars, and (3) hydrothermal mineral phases (phyllosilicates, Fe-Ti oxides, Mn-oxides, and quartz). Altered cone sheets have whole-rock δ18O values ranging from 0·1 to 10·0‰ (n = 22), and whole-rock δD values between -62 and -149‰ (n = 28). Three altered syenite samples have whole-rock δ18O values of 2·5, 1·5, and 0·9‰, and corresponding δD values of -91, -99, and -121‰. The H2O concentrations of the altered cone sheets range from 0·4 to 0·8 wt % (n = 28), and the altered syenites have H2O concentrations of 0·5, 0·5, and 0·6 wt %, respectively. The majority of altered samples are depleted in 18O relative to the typical δ18O range for unaltered trachytes and syenites (δ18O = 6-8‰), indicative of interaction with local meteoric water (δ18O c. -8‰) at temperatures ≥ 150°C. Only one cone sheet sample appears petrographically unaltered and has a typical 'igneous' isotopic composition (δ18O = 7·1‰, δD = -48‰) and a relatively high H2O concentration (2·2 wt %). A weak correlation (r = 0·55) between δD and H2O is observed in the cone sheets, reflecting the combined effects of magmatic H2O exsolution, and subsequent deuteric and hydrothermal alteration. No systematic variation in δ18O or δD was detected across the cone sheet swarm, most likely reflecting overprinting of isotopic compositions during successive intrusive events. However, the highest δ18O values (8·2-10·0‰) occur in clay-bearing cone sheets from the central part of the intrusive complex, suggesting enhanced infiltration of relatively cool meteoric water in this area. Overall, at least three phases of fluid-rock interaction can be distinguished: (1) deuteric alteration (c. 300-500°C) by late magmatic fluids expelled from a solidifying crystal mush; (2) hydrothermal alteration (≥150-300°C) by meteoric water during the final stages of crystallization and/or immediately following solidification of the intrusive complex; (3) retrograde alteration related to the influx of relatively cool (≤150°C) meteoric waters. © The Author 2010. Published by Oxford University Press. All rights reserved.
AUTHOR KEYWORDS: Cone sheets;  Gran Canaria;  Hydrothermal alteration;  Intrusive complexes;  Stable isotopes;  Tejeda caldera
DOCUMENT TYPE: Article
SOURCE: Scopus

Shu, L.a , Wang, B.a  b , Zhu, W.a , Guo, Z.c , Charvet, J.d , Zhang, Y.a 
Timing of initiation of extension in the Tianshan, based on structural, geochemical and geochronological analyses of bimodal volcanism and olistostrome in the Bogda Shan (NW China)
(2010) International Journal of Earth Sciences, pp. 1-17. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956238106&partnerID=40&md5=55a3e83acfb78663ba81c26fa8c6070f
AFFILIATIONS: State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing, 210093, China; 
Institute of Earth Sciences, Academia Sinica, Nankang, 11529, Taiwan; 
School of Earth and Space Sciences, Peking University, Beijing, 100871, China; 
Institut des Sciences de la Terre d'Orléans, UMR 6113, 1A rue de la Férollerie, Orléans, 45100, France
ABSTRACT: This paper describes an olistostrome formation and accompanied bimodal volcanic rocks occurring in the Baiyanggou area, south of Bogda Shan. The main lithotectonic units consist of olistostrome, volcanic rocks and turbidite. The olistostrome is tectonically underlain by Upper Carboniferous limestone and sandstone along a NEE-trending detachment fault. Paleo-growth fault is locally observed. The olistostrome unit includes plenty of blocks of limestone, sandstone, rhyolite and volcaniclastic rocks, and a matrix of graywacke. Limestone blocks are dated as Pennsylvanian-Bashkirian in age by the coral and brachiopod fossils that are extensively recognized in the Upper Carboniferous strata. The volcanic unit consists of pillowed and massive basalt and rhyolite, the latter occur as an 8- to 10-meter-thick layer above the olistostrome unit. The turbidite unit is mainly composed of chert, siliceous mudstone and sandstone, within which the Bouma sequence can be locally recognized. Meter-wide gabbro and diabase dykes intrude these three units. Geochemically, rhyolites are characterized by high ACNK value of &gt;1.1, depletion of Ba, Nb and Sm, and enrichment in Rb, Th and Zr. Basaltic rocks are rich in K2O, they show a LREE-enriched pattern and depletion in Ba, Nb and Zr, and enrichment in Ti, Ce and Hf, similar to continental rift-type tholeiite series. A gabbro porphyrite intruding the olistostrome was dated at 288 ± 3 Ma by a sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb method, and a rhyolite at 297 ± 2 Ma by a laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) zircon U-Pb method. The Baiyanggou olistostrome and accompanying bimodal volcanic series are linked to an extensional setting that developed in the south of the Bogda Shan. Several lines of evidence, e.g. occurrence of large-scale strike-slip shear zones, large number of mantle-derived magmatic rocks and available geochronological data, demonstrate a significant geodynamic change from convergence to extension in the Chinese Tianshan belt, even in the whole Central Asian Orogenic Belt. The extension in the Chinese Tianshan belt is initiated at ca. 300 Ma, i.e. around Carboniferous-Permian boundary times, and the peak period of intra-plate magmatism occurred in the interval of 300-250 Ma. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Bimodal volcanic rocks;  Bogda Shan;  Central Asian Orogenic Belt;  Early Permian;  Olistostrome;  Tianshan;  Zircon U-Pb dating
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Underwood, M.B.a , Saito, S.b , Kubo, Y.c 
IODP expedition 322 drills two sites to document inputs to the Nankai Trough Subduction Zone
(2010) Scientific Drilling, (10), pp. 14-25. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78651550040&partnerID=40&md5=c31f79ef7741ce1489abd64f8287f091
AFFILIATIONS: Department of Geological Sciences, University of Missouri, Columbia, MO 65203, United States; 
Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan; 
Center for Deep Earth Exploration, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan
ABSTRACT: The primary goals during Expedition 322 of the Integrated Ocean Drilling Program were to sample and log the incoming sedimentary strata and uppermost igneous basement of the Shikoku Basin, seaward of the Nankai Trough (southwestern Japan). Characterization of these subduction inputs is one piece of the overall science plan for the Nankai Trough Seismogenic Zone Experiment. Before we can assess how various material properties evolve down the dip of the plate interface, and potentially change the fault's behavior from stable sliding to seismogenic slip, we must determine the initial pre-subduction conditions. Two sites were drilled seaward of the trench to demonstrate how facies character and sedimentation rates responded to bathymetric architecture. Site C0011 is located on the northwest flank of a prominent basement high (Kashinosaki Knoll), and Site C0012 is located near the crest of the seamount. Even though significant gaps remain in the coring record, and attempts to recover wireline logs at Site C0012 failed, correlations can be made between stratigraphic units at the two sites. Sedimentation rates slowed down throughout the condensed section above the basement high, but the seafloor relief was never high enough during the basin's evolution to prevent the accumulation of sandy turbidites near the crest of the seamount. We discovered a new stratigraphic unit, the middle Shikoku Basin facies, which is typified by late Miocene volcaniclastic turbidites. The sediment-basalt contact was recovered intact at Site C0012, giving a minimum basement age of 18.9 Ma. Samples of interstitial water show a familiar freshening trend with depth at Site C0011, but chlorinity values at Site C0012 increase above the values for seawater toward the basement contact. The geochemical trends at Site C0012 are probably a response to hydration reactions in the volcaniclastic sediment and diffusional exchange with seawater-like fluid in the upper igneous basement. These data are important because they finally establish an authentic geochemical reference site for Nankai Trough, unaffected by dehydration reactions, and they provide evidence for active fluid flow within the upper igneous crust. Having two sets of geochemical profiles also shows a lack of hydrogeological connectivity between the flank and the crest of the Kashinosaki Knoll.
DOCUMENT TYPE: Article
SOURCE: Scopus

Herman, A.B.a , Spicer, R.A.b 
Mid-Cretaceous floras and climate of the Russian high Arctic (Novosibirsk Islands, Northern Yakutiya)
(2010) Palaeogeography, Palaeoclimatology, Palaeoecology, 295 (3-4), pp. 409-422. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956010538&partnerID=40&md5=a7427dedff2f2c59de87707e79283b27
AFFILIATIONS: Geological Institute, Russian Academy of Sciences, 7 Pyzhevskii Pereulok, 119017 Moscow, Russian Federation; 
Department of Earth and Environmental Sciences, Centre for Earth, Planetary, Space and Astronomical Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom
ABSTRACT: Two mid-Cretaceous floras collected in terrigenous and volcaniclastic deposits of the Novosibirsk Islands in the Russian high Arctic were studied. These floras are the most poleward mid-Cretaceous floras known and existed at palaeolatitudes up to 82-85° N. These represent our best insight into polar conditions at one of the warmest intervals in Earth history. An Albian flora from the Balyktakh Formation of the Kotel'nyi Island comprises 40 species of ferns, bennettites, cycadophytes, ginkgoaleans, czekanowskialeans, conifers and gymnosperms incertae sedis. This flora is most similar to the Albian Buor-kemuss Flora widespread in the Arctic Siberia and Alaska and, to a lesser extent, to the Aptian Silyap Flora of Siberia. A Turonian flora from the Derevyannye Gory Formation on the Novaya Sibir' Island includes approximately 50 taxa of ferns, ginkgoaleans, conifers and angiosperms. This flora exhibits plants common for the early Cretaceous as well as taxa typical for Cenomanian-Senonian, which implies that the age of the plant-bearing deposits is likely to be Turonian. The Cretaceous climate has often been described as 'warm' with a higher degree of equability than today with the near-polar regions in particular being much warmer than today. Our estimates using CLAMP and a new global gridded climate calibration demonstrate that for the Turonian Novaya Sibir' Flora plant physiognomy reflects a humid climate with warm summers and mild frost-free winters: the mean annual temperature is estimated to have been +. 9.2 ± 2.2°C, the warm month mean temperature +. 17.2 ± 2.8°C, the cold month mean temperature +. 1.1 ± 3.8°C and the mean growing season precipitation 537 ± 392. mm. These temperature parameters indicate that within 900. km of the Turonian North Pole the climate was similar to that of modern temperate, or even warm-temperate, zones but must have differed considerably in having pronounced high-latitude sunlight seasonality. The ecology of the late Cretaceous Arctic plants reflects their adaptation to this climate. Synchronous shedding of foliage (deciduousness) was by far the most common strategy and retention of leaves year round (evergreenness) was also viable for a small number of taxa. Large deciduous leaves typical for the Cretaceous Arctic dicots probably reflect the combination of a warm and humid climate with high-latitude light regime: long days in summer and predominance of relatively weak and mostly diffuse sunlight. The large range of leaf size in a given plant species of Arctic angiosperms was most probably linked to the seasonal character of annual shoot development. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Arctic;  Cretaceous;  Fossil plants;  Novosibirsk Islands;  Palaeoecology;  Warm climate
DOCUMENT TYPE: Article
SOURCE: Scopus

Gallego, A.a , Russo, R.M.a , Comte, D.b , Mocanu, V.I.c , Murdie, R.E.d , Vandecar, J.C.e 
Seismic noise tomography in the Chile ridge subduction region
(2010) Geophysical Journal International, 182 (3), pp. 1478-1492. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955721949&partnerID=40&md5=2425321a7004719f4e571f85262ff3b6
AFFILIATIONS: Department of Geological Sciences, University of Florida, P.O. Box 112120, 241 Williamson Hall, Gainesville, FL 32611, United States; 
Department de Geofisica, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile; 
Department of Geophysics, Bucharest University, 6 Traian Vuia Street, RO-7139 Bucharest 1, Romania; 
Gold Fields Australia, St Ives Gold Mine, P.O. Box 359, Kambalda, WA 6442, Australia; 
DTM, Carnegie Inst. of Washington, 2541 Broad Branch Road, Washington DC 20015, United States
ABSTRACT: We used cross-correlation of ambient seismic noise recorded in the Chile Triple Junction (CTJ) region to estimate interstation surface wave time-domain Green's functions, and then inverted traveltimes to obtain crustal surface wave velocity models. Interstation distances within the Chile Ridge Subduction Project (CRSP) temporary seismic network ranged from 40 to ~100 km. We selected 365 d, and cross-correlated and stacked 24 hr of vertical component data at 38 stations pairs, resulting in nominally 703 traveltimes along assumed-straight interstation paths. Velocities in 2-D cells of 30 km × 30 km were calculated using a linear least-squares inversion of the Rayleigh wave group velocity traveltimes. Furthermore we performed a Rayleigh wave group velocity dispersion analysis to estimate the sensitivity of different period waves at depth and to calculate a 3-D shear velocity model of the Patagonian crust. The process was applied to cross correlation pairs determined in two period bands, 5-10 s, corresponding to shallow crustal velocities down to approximately 10 km depth, and 10-20 s, for velocities down to around 20 km. Our results show that cell velocities correlate well with known geological features. We find high-crustal velocities where the Patagonian Batholith outcrops or is likely present at depth, and low velocities correlate with the active volcanic arc of the Southern Volcanic Zone and the subducted Chile ridge in Taitao peninsula, where thermal activity of hot springs is present. High velocities in the mountainous portions of the southeastern study area appear to correlate with outcropping older metamorphic units. Low velocity in the east correlate with sequences of volcaniclastic deposits. © 2010 The Authors Journal compilation © 2010 RAS.
AUTHOR KEYWORDS: Continental margins: convergent;  Crustal structure;  Rheology: crust and lithosphere;  Surface waves and free oscillations;  Wave propagation;  Wave scattering and diffraction
DOCUMENT TYPE: Article
SOURCE: Scopus

Stewart, R.B., Németh, K., Cronin, S.J.
Is Efate (Vanuatu, SW Pacific) a result of subaerial or submarine eruption? An alternative model for the 1 Ma Efate Pumice Formation
(2010) Central European Journal of Geosciences, 2 (3), pp. 306-320. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77957681451&partnerID=40&md5=1b27245b9a4a799ec8253a569358bca9
AFFILIATIONS: Volcanic Risk Solutions, CS-INR, Massey University, Palmerston North, New Zealand
ABSTRACT: The Efate Pumice Formation (EPF) is a trachydacitic volcaniclastic succession widespread in the central part of Efate Island and also present on Hat and Lelepa islands to the north. The volcanic succession has been inferred to result from a major, entirely subaqueous explosive event north of Efate Island. The accumulated pumice-rich units were previously interpreted to be subaqueous pyroclastic density current deposits on the basis of their bedding, componentry and stratigraphic characteristics. Here we suggest an alternative eruptive scenario for this widespread succession. The major part of the EPF is distributed in central Efate, where pumiceous pyroclastic rock units several hundred meters thick are found within fault scarp cliffs elevated about 800 m above sea level. The basal 200 m of the pumiceous succession is composed of massive to weakly bedded pumiceous lapilli units, each 2-3 m thick. This succession is interbedded with wavy, undulatory and dune bedded pumiceous ash and fine lapilli units with characteristics of co-ignimbrite surges and ground surges. The presence of the surge beds implies that the intervening units comprise a subaerial ignimbrite-dominated succession. There are no sedimentary indicators in the basal units examined that are consistent with water-supported transportation and/or deposition. The subaerial ignimbrite sequence of the EPF is overlain by a shallow marine volcaniclastic Rentanbau Tuffs. The EPF is topped by reef limestone, which presumably preserved the underlying EPF from erosion. We here propose that the EPF was formed by a combination of initial subaerial ignimbrite-forming eruptions, followed by caldera subsidence. The upper volcaniclastic successions in our model represent intra-caldera pumiceous volcaniclastic deposits accumulated in a shallow marine environment in the resultant caldera. The present day elevated position of the succession is a result of a combination of possible caldera resurgence and ongoing arc-related uplift in the region.
AUTHOR KEYWORDS: caldera;  dacite;  explosive;  ignimbrite;  phreatomagmatic;  pumice;  regional uplift;  rhyolite;  subaqueous;  subduction
DOCUMENT TYPE: Article
SOURCE: Scopus

Russo Ermolli, E.a , Sardella, R.b , Di Maio, G.c , Petronio, C.b , Santangelo, N.d 
Pollen and mammals from the late Early Pleistocene site of Saticula (Sant'Agata de' Goti, Benevento, Italy)
(2010) Quaternary International, 225 (1), pp. 128-137. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955770925&partnerID=40&md5=bb0dd30c245596fcea1083ffd44bf884
AFFILIATIONS: Dipartimento di Arboricoltura, Botanica e Patologia vegetale, Università di Napoli Federico II, Via Università 100, 80050 Portici (Napoli), Italy; 
Dipartimento di Scienze della Terra, Sapienza, Università di Roma, Italy; 
GEOMED srl, Scafati (Salerno), Italy; 
Dipartimento di Scienze della Terra, Università di Napoli Federico II, Italy
ABSTRACT: A fluvio-lacustrine succession was discovered in 1995 at Saticula, near Sant'Agata de' Goti (Benevento), below a thick volcaniclastic deposit sealed by the " Ignimbrite Campana" formation (39. ka). Vertebrate fossil remains and pollen were recovered in the excavated sections. Pollen analysis allowed recognition of two pollen zones, the first being characterised by a Quercus-Carya mixed deciduous forest which was probably present in the plain and on the slopes surrounding the Caudina valley basin. The following samples record a drastic decrease in Carya pollen grains and the contemporary increase in herbs and Pinus. A more open environment established around the river shores due to a climate shift towards dryer conditions. Most of the vertebrate remains were found in the upper portion of the succession corresponding to the zone with reduced Carya pollen. The fossil mammal assemblage includes Hippopotamus antiquus, Axis eurygonos, Megacerini indet., Equus suessenbornensis and Stephanorhinus cf. S. hundsheimensis. In addition, a partial unerupted molar of an elephantid, two hyena coprolites and fragments of rodent teeth were identified. The high amount of Carya at the base of the succession represents the most peculiar feature of the Saticula floral record and was used as a reference for its chronological constraint. Comparison with other Italian pollen successions allowed the Saticula record to be tentatively ascribed to the late Early Pleistocene. After that period, Carya was never recorded in such high amounts and gradually disappeared from the Italian flora following a heterochronous latitudinal gradient. The Saticula mammal assemblage is in agreement with the chronological framework suggested by pollen data. © 2009 Elsevier Ltd and INQUA.
DOCUMENT TYPE: Article
SOURCE: Scopus

Kröner, A.a  b , Lehmann, J.c  d , Schulmann, K.c , Demoux, A.a  b , Lexa, O.d  e , Tomurhuu, D.f , Štípská, P.c , Liu, D.g , Wingat, M.T.D.h 
Lithostratigraphic and geochronological constraints on the evolution of the central Asian orogenic belt in SW Mongolia: Early paleozoic rifting followed by late paleozoic accretion
(2010) American Journal of Science, 310 (7), pp. 523-574. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78149338881&partnerID=40&md5=cedaced90e0dffa0c09238649fec1d86
AFFILIATIONS: Institut für Geowissenschaften, Universität Mainz, Becherweg 21, D-55099 Mainz, Germany; 
Beijing SHRIMP Center, Chinese Academy of Geological Sciences, Beijing 100037, China; 
Institut de Physique du Globe de Strasbourg, IPGS-UMR 7516, CNRS, Université de Strasbourg, 3 rue Michel-Ange, F-67084 Strasbourg, France; 
Czech Geological Survey, Klárov 3, 118 21 Praha 1, Czech Republic; 
IPSG, Univerzita Karlova, Albertov 6, Praha 2, Czech Republic; 
Institute of Geology and Mineral Resources, Mongolian Academy of Sciences, P. O. Box 118, Ulaanbaatar 210351, Mongolia; 
Beijing SHRIMP Center, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, 100037 Beijing, China; 
Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia
ABSTRACT: New SHRIMP U-Pb and evaporation Pb-Pb zircon ages, together with a revision of the lithostratigraphy of "suspect" terranes in SW Mongolia, suggest that the collage of continental and oceanic units in this region resulted from recurrent magmatic reworking and deformation of Silurian-early Devonian proximal and distal passive margin sequences of the Paleo-Asian Ocean. The zircon ages from early Ordovician volcaniclastic rocks and syntectonic felsic dikes reveal an heterogeneous stretching of the Precambrian Dzabkhan microcontinent (Lake Zone basement) during the Ordovician, followed by the development of a carbonate platform on a proximal margin (Gobi-Altai Zone), serpentinite breccias and Silurian chert sequences on a distal margin and possibly also the formation of oceanic crust. The assumed early Neoproterozoic South Gobi continental zone may either represent an allochthonous block detached from Dzabkhan or, less likely, the conjugate margin of a Paleo-Asian continental rift. Early Devonian volcanism subsequently affected both types of margins with back-arc spreading centers and arcs located in the core of the future Trans-Altai Zone. During the late Devonian to early Carboniferous a Japan-type magmatic arc developed on the previously stretched continental crust of the Gobi-Altai Zone. This event was associated with shortening of the entire domain, exhumation of the deep arc core and formation of intramontane basins with Devonian and Carboniferous detrital zircons of the adjacent Lake Zone continent. Clastic, flysch-type sedimentation occurred on the former distal margin and in oceanic areas. During this early Carboniferous contraction event the continental and oceanic units were imbricated and accreted to the continent in the north. Subsequently, late Carboniferous volcanic arc sequences and a Japan-type magmatic arc developed on the Trans-Altai oceanic crust and the southern South Gobi Zone, respectively. Finally, a Permian thermal event was localized in the Gobi-Altai-Lake Zone contact domain and was responsible for formation of Permian grabens, bimodal volcanism and substantial melting of the accreted crust.
AUTHOR KEYWORDS: Accretionary tectonics;  Central Asian orogenic belt;  Mongolia;  Paleozoic;  Tectono-stratigraphy;  Zircon geochronology
DOCUMENT TYPE: Article
SOURCE: Scopus

Sak, P.B.a , Navarre-Sitchler, A.K.b , Miller, C.E.a , Daniel, C.C.c , Gaillardet, J.d , Buss, H.L.e , Lebedeva, M.I.f , Brantley, S.L.f 
Controls on rind thickness on basaltic andesite clasts weathering in Guadeloupe
(2010) Chemical Geology, 276 (3-4), pp. 129-143. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956178982&partnerID=40&md5=b23493b1034ded4a038a40fb712167dd
AFFILIATIONS: Department of Earth Sciences, Dickinson College, Carlisle, PA 17013, United States; 
Environmental Science and Engineering Division, Colorado School of Mines, Golden, CO 80401, United States; 
Department of Geology, Bucknell University, Lewisburg, PA 17837, United States; 
Laboratoire de Géochimie et Cosmochimie, Institut de Physique du Globe de Paris, Universite Paris 7, Paris, France; 
US Geological Survey, 345 Middlefield Rd. MS 420, Menlo Park, CA 94040, United States; 
Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, United States
ABSTRACT: A clast of low porosity basaltic andesite collected from the B horizon of a soil developed on a late Quaternary volcaniclastic debris flow in the Bras David watershed on Basse-Terre Island, Guadeloupe, exhibits weathering like that observed in many weathered clasts of similar composition in other tropical locations. Specifically, elemental profiles measured across the core-rind interface document that primary minerals and glass weather to Fe oxyhydroxides, gibbsite and minor kaolinite in the rind. The earliest reaction identified in the core is oxidation of Fe in pyroxene but the earliest reaction that creates significant porosity is plagioclase dissolution. Elemental loss varies in the order Ca≈Na&gt;K≈Mg&gt;Si&gt;Al&gt;Fe≈P»Ti, consistent with the relative reactivity of phases in the clast from plagioclase≈pyroxene≈glass&gt;apatite&gt;ilmenite. The rind surrounds a core of unaltered material that is more spherical than the original clast. The distance from the core-rind boundary to a visually prominent rind layer, L, was measured as a proxy for the rind thickness at 36 locations on a slab cut vertically through the nominal center of the clast. This distance averaged 24.4±3.1mm. Maximum and minimum values for L, 35.8 and 20.6mm, were observed where curvature of the core-rind boundary is greatest (0.12mm-1) and smallest (0.018mm-1) respectively. Extrapolating from other rinds in other locations, the rate of rind formation is estimated to vary by a factor of about 2 (from ~4 to 7×10-14ms-1) from low to high curvature. The observation of a higher rate of rind formation for a higher curvature interface is consistent with a diffusion-limited model for weathering rind formation. The diffusion-limited model predicts that, like rind thickness, values of the thickness of the reaction front (h) for a given reaction, defined as the zone over which a parent mineral such as plagioclase completely weathers to rind material, should also increase with curvature. Values of h were quantified as a function of interface curvature using bulk chemical analysis (500&lt;h&lt;2000μm). Values of h were also quantified by measuring loss of matrix glass and increase in porosity as a function of curvature. In contrast to rind thickness, h shows no consistent increase with curvature. This contradiction is attributed to the mm-scale roughness of the interface which is related to phenocryst grain size. Therefore, the overall rind formation rate is strongly affected by curvature measured at the scale of the clast, while mineral reaction rates documented by reaction front thickness are strongly affected by curvature at the scale of phenocrysts. Similarly, the weathering advance rate (ms-1) for the entire Bras David watershed can be extrapolated from the clast weathering rate if roughness at the watershed scale equals values of approximately 400-800. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Basalt weathering;  Chemical weathering;  Guadeloupe;  Weathering rinds
DOCUMENT TYPE: Article
SOURCE: Scopus

Pereira, M.F.a , Silva, J.B.b , Ribeiro, C.a 
The role of bedding in the formation of fault-fold structures, Portalegre-Esperança transpressional shear zone, SW Iberia
(2010) Geological Journal, 45 (5-6), pp. 521-535. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956736634&partnerID=40&md5=67fe94e58de457cb5da94a15deb24c1b
AFFILIATIONS: Departamento de Geociências, Centro de Geofísica de Évora, Universidade de Évora, Portugal; 
Departamento de Geologia, Faculdade de Ciências, Lattex-IDL, Universidade de Lisboa, Portugal
ABSTRACT: Fold-fault structures within a major transpressional shear zone of the SW Iberian Massif were investigated by combining geological mapping, cross-section analysis and microtectonic studies. A significant example of contractional deformation is displayed in the Portalegre-Esperança Shear Zone (PESZ) where a heterogeneous Ordovician stratigraphic sequence, showing a strong competence contrast between quartzites, slates and quartzo-feldspathic rocks favoured strain localization and fault nucleation that controlled fold formation. The presence of pelitic layers within the thick-bedded quartzites had probably provided weakness zones that were more favourable for the strain localization than the previous foliation present in the quartzites. The quartzites and the quartzo-feldspathic rocks (granites and volcaniclastic rocks) accommodated heterogeneous high strain developing different degrees of mylonitization. The quartzites with protomylonitic textures are dominant and represent coarse-grained siliciclastic sediments that suffered metamorphism and partial dynamic recrystallization. Ultramylonites occur within discrete high-strain shear zones. It is probable that the strain localization in the PESZ involved both the effect of having layers of different competence and layers or stratigraphic contacts with rocks that experienced grain size reduction dominated by cataclasis and dislocation creep. Folds within quartzites with sub-horizontal to gently plunging hinges vary from closed to open in thick-bedded quartzites and from tight to closed in thin-bedded quartzites. Observed changes in structural style of deformed quartzites, slates and quartzo-feldspathic rocks are interpreted to result from the constraints imposed by the mechanical properties of the different lithologies. As the folds tightened during shortening, the alternating zones of contrasting competence favoured the disruption of the bedding. The deformation history in the PESZ was dominated by thrusting and strike-slip faulting along incompetent layers that locally developed staircase geometry and transected the lower Ordovician stratigraphic sequence. The kinematic model proposed for the PESZ is consistent with the models of transpressional shear zones stretched along strike with the development of coeval strike-slip and low angle oblique-slip faults associated to active buckle folds with axes parallel to the principal extension direction. © 2010 John Wiley & Sons, Ltd.
AUTHOR KEYWORDS: Competence contrast;  Fault nucleation and propagation;  Folds formation;  Mylonitization;  Transpression
DOCUMENT TYPE: Article
SOURCE: Scopus

Clemens, J.D.a , Benn, K.b  c 
Anatomy, emplacement and evolution of a shallow-level, post-tectonic laccolith: The Mt Disappointment pluton, SE Australia
(2010) Journal of the Geological Society, 167 (5), pp. 915-941. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956965412&partnerID=40&md5=a21fdeb0ef2b454f0b229a70baf779a4
AFFILIATIONS: Department of Earth Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa; 
Department of Earth Sciences, University of Ottawa, Ottawa, ON K1N6N5, Canada; 
TerraCognita Geological Consulting Inc., 4874 St. Clair Parkway, Port Lambton, ON N0P 2B0, Canada
ABSTRACT: The Late Devonian, high-level, post-orogenic Mt Disappointment pluton was emplaced as a nested laccolith. Field observations and magnetic fabric (anisotropy of magnetic susceptibility) data show that the monzogranitic to granodioritic magmas entered the pluton from a central, linear feeder. The first set of magmas solidified to a non-megacrystic unit and the second to a unit carrying K-feldspar megacrysts. Emplacement was accommodated partly by uplift of the overburden on brittle marginal faults. The magmas were produced through mid- to deep crustal (<600 MPa) partial melting of a source containing both 'igneous' and 'sedimentary' rocks, possibly a package of volcaniclastic and aluminous metagreywackes. The spectrum of magma compositions was not formed through any differentiation or magma mixing process. At the source, the melt compositions varied as a result of mixing between liquids derived from the two main source rocks, with variations in the amount of plagioclase component that entered the melt. The degree of entrainment of peritectic orthopyroxene and ilmenite appears to have controlled the Fe, Mg and Ti contents of the magma batches. A variety of evidence suggests that magma withdrawal from the protolith was rapid and episodic. The magma batches so formed were emplaced into the growing pluton essentially without further chemical evolution. © 2010 Geological Society of London.
DOCUMENT TYPE: Article
SOURCE: Scopus

Seghedi, I.a , Szakács, A.a  b , Roşu, E.c , Pécskay, Z.d , Gméling, K.e 
Note on the evolution of a Miocene composite volcano in an extensional setting, Zĝrand Basin (Apuseni Mts., Romania)
(2010) Central European Journal of Geosciences, 2 (3), pp. 321-328. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77957673727&partnerID=40&md5=8b9ea90c8ba9eca8cca671ea97a40d5b
AFFILIATIONS: Institute of Geodynamics, Romanian Academy, 19-21, Jean-Luis Calderon str., RO-020032 Bucharest, Romania; 
Dept. of Environmental Sciences, Sapienţia University, Matei Corvin str., 4, RO-400112 Cluj-Napoca, Romania; 
Geological Institute of Romania, 1, Caransebeş str. 32, RO-78344 Bucharest, Romania; 
Institute of Nuclear Research, Hungarian Academy of Sciences, Bem ter 18/c, H-4001 Debrecen, Hungary; 
Institute of Isotopes, Hungarian Academy of Sciences, 29-33, Konkoly Thege-M. str., H-1121 Budapest, Hungary
ABSTRACT: Bontĝu is a major eroded composite volcano filling the Miocene Zĝrand extensional basin, near the junction between the Codru-Moma and Highiş-Drocea Mountains, at the tectonic boundary between the South and North Apuseni Mountains. It is a quasi-symmetric structure (16-18 km in diameter) centered on an eroded vent area (9×4 km), buttressed to the south against Mesozoic ophiolites and sedimentary deposits of the South Apuseni Mountains. The volcano was built up in two sub-aerial phases (14-12.5 Ma and 11-10 Ma) from successive eruptions of andesite lava and pyroclastic rocks with a time-increasing volatile budget. The initial phase was dominated by emplacement of pyroxene andesite and resulted in scattered individual volcanic lava domes associated marginally with lava flows and/or pyroclastic block-and-ash flows. The second phase is characterized by amphibole-pyroxene andesite as a succession of pyroclastic eruptions (varying from strombolian to subplinian type) and extrusion of volcanic domes that resulted in the formation of a central vent area. Numerous debris flow deposits accumulated at the periphery of primary pyroclastic deposits. Several intrusive andesitic-dioritic bodies and associated hydrothermal and mineralization processes are known in the volcano vent complex area. Distal epiclastic deposits initially as gravity mass flows and then as alluvial volcaniclastic and terrestrial detritic and coal filled the basin around the volcano in its western and eastern part.Chemical analyses show that lavas are calc-alkaline andesites with SiO2 ranging from 56-61%. The petrographical differences between the two stages are an increase in amphibole content at the expense of two pyroxenes (augite and hypersthene) in the second stage of eruption; CaO and MgO contents decrease with increasing SiO2. In spite of a ~4 Ma evolution, the compositions of calc-alkaline lavas suggest similar fractionation processes. The extensional setting favored two pulses of short-lived magma chamber processes.
AUTHOR KEYWORDS: andesite;  Apuseni Mountains;  composite volcano;  extensional setting
DOCUMENT TYPE: Article
SOURCE: Scopus

Georgiopoulou, A.a , Masson, D.G.b , Wynn, R.B.b , Krastel, S.c 
Sahara slide: Age, initiation, and processes of a giant submarine slide
(2010) Geochemistry, Geophysics, Geosystems, 11 (7), art. no. Q07014, . 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955337180&partnerID=40&md5=2a2e1cf1c1e6d382d0371646a397ad35
AFFILIATIONS: National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, United Kingdom; 
School of Geological Sciences, University College Dublin, UCD Science Centre (West), Dublin 4, Ireland; 
Leibniz Institute of Marine Sciences, University of Kiel (IFM-GEOMAR), Wischhofstrasse 1-3, Gebude 4, D-24148 Kiel, Germany
ABSTRACT: The Sahara Slide is a giant submarine landslide on the northwest African continental margin. The landslide is located on the open continental slope offshore arid Western Sahara, with a headwall at a water depth of ∼2000 m. High primary productivity in surface waters drives accumulation of thick fine-grained pelagic/hemipelagic sediment sequences in the slide source area. Rare but large-scale slope failures, such as the Sahara Slide that remobilized approximately 600 km3 of sediment, are characteristic of this sedimentological setting. Seismic profiles collected from the slide scar reveal a stepped profile with two 100 m high headwalls, suggesting that the slide occurred retrogressively as a slab-type failure. Sediment cores recovered from the slide deposit provide new insights into the process by which the slide eroded and entrained a volcaniclastic sand layer. When this layer was entrained at the base of the slide it became fluidized and resulted in low apparent friction, facilitating the exceptionally long runout of ∼900 km. The slide location appears to be controlled by the buried headwall of an older slope failure, and we suggest that the cause of the slide relates to differential sedimentation rates and compaction across these scarps, leading to local increases of pore pressure. Sediment cores yield a date of 50-60 ka for the main slide event, a period of global sea level rise which may have contributed to pore pressure buildup. The link with sea level rising is consistent with other submarine landslides on this margin, drawing attention to this potential hazard during global warming. Copyright 2010 by the American Geophysical Union.
AUTHOR KEYWORDS: debris flow;  northwest Africa;  Sahara Slide;  slope instability;  tsunami;  turbidite
DOCUMENT TYPE: Article
SOURCE: Scopus

Sohn, Y.K.a , Yoon, S.-H.b 
Shallow-marine records of pyroclastic surges and fallouts over water in Jeju Island, Korea, and their stratigraphic implications
(2010) Geology, 38 (8), pp. 763-766. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955965457&partnerID=40&md5=15fc1bbdd5ef4d1777e36823a00f2e21
AFFILIATIONS: Department of Earth and Environmental Sciences, Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, South Korea; 
Faculty of Ocean Science, Marine and Environmental Research Institute, Jeju National University, Jeju 690-756, South Korea
ABSTRACT: Explosive volcanism results in a wide range of volcaniclastic deposits in many of Earth's subaerial and subaqueous environments. In this paper, we introduce a unique, shallow-marine volcaniclastic deposit from Jeju Island, Korea, for which the materials were transported to the water surface by pyroclastic clouds and then settled from the surface as they were entrained in the water. The deposition occurred under alternating currents and still waters, which is most plausibly attributed to tidal processes. Mud flasers or drapes intercalated in the deposit, which indicate periods of slack water during tidal cycles, suggest that the deposit accumulated in a very short period of a fortnight or a month, about a million times faster than the adjacent sedimentary strata. Because of the unusually high sedimentation rate, the volcaniclastic deposit could record the "usual" fair-weather processes in the depositional site at a resolution that is almost never provided by ordinary sedimentary deposits. This finding highlights the biases in Earth's stratigraphic records and teaches us that volcanic deposits, commonly regarded as the products of catastrophic events, can in some cases record more faithfully the ordinary and usual processes that nonvolcanic deposits cannot. © 2010 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Chough, S.K.a , Sohn, Y.K.b 
Tectonic and sedimentary evolution of a Cretaceous continental arc-backarc system in the Korean peninsula: New view
(2010) Earth-Science Reviews, 101 (3-4), pp. 225-249. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954661258&partnerID=40&md5=1f54822a415131c7e3a97dd4915301da
AFFILIATIONS: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, South Korea; 
Department of Earth and Environmental Sciences and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, South Korea
ABSTRACT: This paper focuses on the tectonic and sedimentary evolution of the Cretaceous volcanic rocks and nonmarine successions in the southeastern part of the Korean peninsula, which constitute an ancient continental arc system. The arc system (Gyeongsang Arc System), comprising an arc platform (Gyeongsang Volcanic Arc) and a backarc basin (Gyeongsang Backarc Basin), was a southwestward extension of the Japanese Arc formed by oblique northward subduction of the proto-Pacific (Izanagi) plate under the Asian continent. The backarc basin was initiated in the southeastern part of the Korean peninsula in the Early Cretaceous as a narrow NS-trending trough. The basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated. Sediments were deposited in streamflow-dominated alluvial fans adjacent to the fault-bounded basin margin in the north and low-gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers. Sediments were also derived from the western highland margin, draining Precambrian to Jurassic basement rocks. The initially narrow trough progressively expanded toward the east, resulting in eastward migration of depocenters that eventually generated a broad fluvio-lacustrine plain fringing the volcanic arc platform. The arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network. Pyroclastic density currents and landslides, which originated from the arc platform, also entered the basin. In addition, extrusion of basaltic volcanic rocks was continual within the basin during basin expansion. The resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin. In the Late Cretaceous, andesitic to rhyolitic volcanism became climactic in the arc platform, producing a number of calderas or volcanotectonic depressions. Volcaniclastic aprons fringing the arc platform encroached upon the basin fill. Intraarc basins, produced by sinistral shearing of the arc platform, received sediments from active volcanoes and footwalls of contemporaneous faults, forming small-scale streamflow-dominated alluvial fans and floodplains with later development of a deep lake. Overall, the Gyeongsang Arc System formed under an extensional or transtensional (sinistral strike-slip) stress regime, suggesting that the subducting and the overriding plates were not strongly coupled. Both the volcanic arc and the backarc basin ceased to develop as volcanic activities shifted progressively eastward in the Paleogene accompanied with rollback of the subduction of the Izanagi plate. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Arc volcanism;  Backarc basin;  Basin evolution;  Continental arc;  Gyeongsang Basin;  Intraarc basin;  Stratigraphic development
DOCUMENT TYPE: Review
SOURCE: Scopus

Corfield, R.I.a , Carmichael, S.a , Bennett, J.a , Akhter, S.a , Fatimi, M.a , Craig, T.b 
Variability in the crustal structure of the West Indian Continental Margin in the Northern Arabian Sea
(2010) Petroleum Geoscience, 16 (3), pp. 257-265. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955505158&partnerID=40&md5=a01a35462f633c12de85ec4786655e60
AFFILIATIONS: BP Exploration, Chertsey Road, Sunbury-on-Thames, Middlesex TW16 7LN, United Kingdom; 
University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
ABSTRACT: In this case study of the West Indian Continental Margin we present an interpretation of a volcanic margin structure based on regional mapping of high quality 2D seismic data in conjunction with regional satellite derived gravity data and selected subsidence analyses. The area shows many classic characteristics of a volcanic-type margin. Volcanic facies identified and mapped along the margin include seaward-dipping reflectors (SDRs), sub-aerial seamounts, clinoform packages interpreted as lava and volcaniclastic delta systems and thick, seismically layered sequences interpreted as volcanically derived sediment deposited in both fluvial and marine environments. The results show major variation in the overall thickness and style of volcanism across the margin both in dip and strike directions which may be related to variability in influence of the Deccan Plume in addition to localization along structural features inherited from older tectonic events. Our interpretation of rapid lateral variation in the thickness of extrusive volcanism has important implications for the distribution, preservation and hydrocarbon potential of the pre-rift sequence across the margin. The interpreted crustal structure also has a major impact on predictions of the historical and present-day heat-flow into the post-rift section. Our interpretation of the timing and distribution of volcanism is consistent with the presence of a broad region of elevated mantle potential temperatures at the time of the final break-up event on the West Indian Continental Margin, commonly attributed to the Deccan/Réunion Plume. Pre-existing structural heterogeneities appear to have played an important part in controlling the distribution of volcanism. Interpreted tectonic subsidence, based on backstripping analysis of the postbreak- up interval, is also shown to be consistent with post-break-up thermal subsidence in combination with dynamic support associated with the elevated mantle temperatures into the Early Eocene. © 2010 EAGE/Geological Society of London.
AUTHOR KEYWORDS: Deccan;  Gravity;  India;  Margin;  Pakistan;  Subsidence;  Volcanic
DOCUMENT TYPE: Article
SOURCE: Scopus

Álvaro, J.J.a , Debrenne, F.b 
The Great Atlasian Reef Complex: An early Cambrian subtropical fringing belt that bordered West Gondwana
(2010) Palaeogeography, Palaeoclimatology, Palaeoecology, 294 (3-4), pp. 120-132. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955273766&partnerID=40&md5=8ee234f7b4e2a6fa61b92f4d90658bcf
AFFILIATIONS: Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Spain; 
13, rue du Long Foin, 91700-Sainte Geneviève des Bois, France
ABSTRACT: The so-called Great Atlasian Reef Complex developed during early Cambrian time throughout the Moroccan margin (Souss Basin) of West Gondwana. According to the syndepositional tectonic activity associated with its intracratonic Ediacaran-Cambrian rift, the great reef complex can be subdivided into four major archaeocyathan-microbial reef episodes:. (i) The Atdabanian episode is recorded by a SW-NE-trending, 400. km long barrier reef that extended across the western Anti-Atlas. It was controlled by large-scale reactivation of an inherited rifting branch, which resulted in the nucleation and growth of linear reef complexes located along its margin. The interplay of block tilting, sharp modifications in accommodation space, and relative sea-level rise led to a composite retrogradational-aggradational reef systems tract, characterized by archaeocyathan-microbial kalyptrate complexes (Tiout Member and Amouslek Formation) that protected stromatolite-dominated, back-barrier environments (lower member of the Igoudine Formation).(ii) The western Anti-Atlas recorded an early Botoman reactivation of the same rifting branch that triggered a lateral migration of frame-building centres of carbonate productivity. As a result, the involved grabens and half-grabens recorded the development of fringing mound complexes (lower Issafen Formation). These occupied some linear intra-platform, deeper depressions capped by marls and shales, whereas laterally equivalent shallower environments recorded the development of patch-reefs and bioherms.(iii) The western Anti-Atlas subsequently recorded a late Botoman interval of tectonic quiescence superimposed to a local interval of progradational pulses. This favoured the nucleation of dispersed archaeocyathan-microbial patch-reefs and bioherms.(iv) A distinct palaeogeographic area is recognized in the southern High Atlas, where the entire Atdabanian-Botoman interval recorded small-scale, synsedimentary block tilting and high rates of volcaniclastic input. As a result, this sector was characterized by the record of microbial and archaeocyathan-microbial patch-reefs and bioherms, preferentially developed on the uplifted parts of tilted blocks.The end of reef development and carbonate productivity in the Souss Basin is related to the progradation of siliciclastic depositional systems (Toyonian regression), considered to have caused the collapse of reef communities throughout West Gondwana. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Archaeocyaths;  Buildup;  Calcimicrobes;  Morocco;  Rift;  Subtropical climate
DOCUMENT TYPE: Article
SOURCE: Scopus

Jauer, C.D.a , Budkewitsch, P.b 
Old marine seismic and new satellite radar data: Petroleum exploration of north west Labrador Sea, Canada
(2010) Marine and Petroleum Geology, 27 (7), pp. 1379-1394. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954660288&partnerID=40&md5=175282238a6559e3db3cf2b0fb90f891
AFFILIATIONS: Bedford Institute of Oceanography, Geological Survey of Canada (Atlantic), Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada; 
Canada Centre for Remote Sensing, Ottawa, ON, Canada
ABSTRACT: This paper presents some new concepts in the petroleum systems of the northern Labrador and southern Baffin Island offshore region of eastern Canada. The focus of this work is the region of the Hekja O-71 gas discovery of 1979 by Aquitaine, one of only five wells drilled between 1976 and 1980 within an area covering some 166,000 square kilometers within the Saglek Basin.This study emerged from a broad scale re-examination of the petroleum potential of this area " from the crust up" using regional reflection, refraction and potential field data. An opportunity to use SAR (synthetic aperture radar) data from the RADARSAT-1 Earth observation satellite was taken to incorporate alternative data sources to support this exploratory review and resource assessment.Examination of the final map of interpreted slick-like features on the sea surface, revealed a close correlation of some of these occurrences to several bathymetric features which have underlying seismic signatures similar to previously identified gas hydrate " pipes" or chimney anomalies as seen in data from offshore Nova Scotia and in the Irish Sea. Globally, many active marine hydrocarbon seeps appear on the seafloor as " pockmarks" ; in this case no seafloor depressions were seen on conventional multi channel 2-D seismic data associated with active seepage. Instead, very distinct mound-like structures are seen associated with seeps at two locations east of Hudson Strait. The presence of significant cold water coral in close proximity to the active seepage sites may show a link between seafloor petroleum seepage and coral reef development similar to that observed offshore Norway.Close examination of the near surface seismic character led to the interpretation of what was originally seen as seismic noise in vintage data, as likely being fluid escape chimneys or gas pipes, along the eastern edge of the Hekja structural complex, where favourable hydrocarbon trapping conditions are present.No active seeps were seen there; this may be due to other factors, such as the nature of the fluids that are escaping or the possibility of self sealing activity by biological agents such as bacterial matting with associated carbonate hard-ground formation.One seep anomaly was noted relatively close to the major basaltic eruptive complex near the Gjoa G-37 well. This may be due to the presence of volcaniclastic- hosted hydrocarbons similar in style to those recently discovered at the Rosebank field in Paleocene volcanics in the Faroe-Shetland Basin. The occurrence of an active seep in a volcanically-dominated terrain raises the potential for a radical shift in accepted types of petroleum leads and where they may occur.The presence of apparent oil seepage versus the past history of finding only gas-prone accumulations is a strong indicator that a second, oil-prone petroleum system exists in the Saglek Basin. The signs of active petroleum systems as shown by oil seep anomalies with confirming seismic evidence of discrete sea floor structures in close proximity makes a compelling argument for re-examining these areas with an eye towards stratigraphic instead of structural plays. © 2010.
AUTHOR KEYWORDS: Basalt;  Cold water corals;  Oil slicks;  Petroleum;  Radarsat;  Saglek Basin;  SAR data;  Sea floor structures;  Seeps;  Seismic interpretation
DOCUMENT TYPE: Article
SOURCE: Scopus

Welkner, D.a  b , Eberhardt, E.a , Hermanns, R.L.c 
Hazard investigation of the Portillo Rock Avalanche site, central Andes, Chile, using an integrated field mapping and numerical modelling approach
(2010) Engineering Geology, 114 (3-4), pp. 278-297. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955171722&partnerID=40&md5=aad58dab758b1553c54d5cac3ed98d31
AFFILIATIONS: Geological Engineering/EOS, University of British Columbia, Vancouver, B.C., Canada; 
BGC Engineering Inc., 500-1045 Howe St., Vancouver, BC, Canada; 
Geological Survey of Norway, International Centre for Geohazards, Trondheim, Norway
ABSTRACT: This paper reports a detailed rock slope hazard investigation of the Portillo Rock Avalanche site located in the rugged mountains of the Andean Cordillera of central Chile. The site is important as it lies along the International Santiago-Mendoza Highway Corridor connecting Chile and Argentina, and a major ski resort is located on its deposits. A number of large lobate-shaped diamicton deposits were mapped and dated by cosmogenic nuclides (36Cl), with the results showing that they correspond to two significant prehistoric rockslide events. An integrated field mapping and numerical modelling investigation was subsequently carried out to assess the threat posed to the area by further rocksliding activity. Distinct-element modelling was used to back analyze the failure mechanism and identify the geological model that best reproduced the Portillo Rock Avalanche failure surface. Results show that a stress-controlled failure at the toe of the slope followed by sliding along volcaniclastic bedding was the likely failure mechanism. A 3-D dynamic runout analysis was carried out to back analyze which combinations of rheologies, material properties and rockslide sequencing were best able to reproduce the current distribution of rockslide deposits. Results indicate that two separate sliding events originating from different sources had occurred, with each involving different combinations of frictional and Voellmy rheologies depending on the level of entrainment that occurred along each travel path.Insights gained from the back analysis were then used to carry out a forward analysis to assess the potential for a recurring major rockslide under several different triggering scenarios. Results suggest that a low probability M 7.8 earthquake would be required to trigger another rockslide from the original source area. The rock slope was otherwise found to be stable, even following high precipitation events. Nevertheless, runout simulations for the estimated large-magnitude earthquake-triggered rockslide volume showed that for both a highly frictional and non-saturated path (i.e. dry season) and a snow covered path (winter), the leading edge of the flow would override part of the International Santiago-Mendoza Corridor with the debris coming to rest in a flat-lying area in the upper part of the valley. Overall, the results from this integrated hazard assessment suggest that the hazard level is low. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Chilean Andes;  Cosmogenic dating;  Rockslide hazard assessment;  Runout analysis;  Stress-controlled failure;  Trigger mechanism analysis
DOCUMENT TYPE: Article
SOURCE: Scopus

Machado, G.a , Hladil, J.b , Slavík, L.b , Koptíková, L.b  c , Moreira, N.d , Fonseca, M.e , Fonseca, P.f 
An Emsian-Eifelian calciturbidite sequence and the possible correlatable pattern of the Basal Choteč Event in Western Ossa-Morena zone, Portugal (Odivelas Limestone)
(2010) Geologica Belgica, 13 (4), pp. 431-446. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954569936&partnerID=40&md5=95818f3fbe8aec7ee407f05a794d11eb
AFFILIATIONS: GeoBioTec, Geoscience Department, University of Aveiro, 3810-193 Aveiro, Portugal; 
Institute of Geology, AS CR, v.v.i. Rozvojová 269, 165 00 Prague 6, Czech Republic; 
Institute of Geology and Palaeontology, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic; 
LIRIO - Laboratório de Investigação de Rochas Industriais e Ornamentais, Espaço Ciência, Convento das Maltezas, 7100-513 Estremoz, Portugal; 
IICT - Instituto de Investigação Científica Tropical, DCN-GeoDES, Tapada da Ajuda 1349-017 Lisboa; 
Geology Department and CeGul, Faculty of Sciences of the University of Lisbon, Edifício C6, Campo Grande, 1749-016 Lisbon, Portugal
ABSTRACT: An Emsian-Eifelian carbonate-volcaniclastic sequence in south-western Ossa-Morena Zone (Portugal) was studied in terms of reef fauna, conodont biostratigraphy, macro- and micro-facies and magnetic susceptibility stratigraphy. The results point to a bracketing between the Po. patulus and T. australis conodont biozones (uppermost Emsian - middle-late Eifelian). The field data, facies analysis and reef fauna indicate that the sequence is composed entirely of calciturbidite and debris-flow deposits (intercalated with hemipelagic tuffites) related to a (up-slope) reefal system resting on top of volcanic buildings within a large volcanic complex. The purity of the limestones does not seem to be generally influenced by volcanic contributions. Although with some uncertainties, the first part of the section seems to show pre-,syn- and post-Basal Choteč Event (BCE) beds as recorded by significant shifts in lithofacies and magnetic susceptibility signal. A tentative interregional correlation with magnetic susceptibility curves is suggested with sections in Morocco, Nevada (USA) and Uzbekistan.
AUTHOR KEYWORDS: Basal Choteč Event;  Emsian-Eifelian boundary;  Magnetic susceptibility;  Odivelas Limestone;  Sedimentology;  Stratigraphy;  SW Ossa-Morena Zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Domínguez, E.A.a , Iglesias, C.b , Dondi, M.c , Guarini, G.c , Raimondo, M.c 
Interrelationships between kaolin mineralogy and ceramic behavior: A case-study from Patagonia, Argentina
(2010) SME Annual Meeting and Exhibit 2010, pp. 529-531. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954241126&partnerID=40&md5=e1c49a449e10509a0393df70633f41d0
AFFILIATIONS: Univ. Nacional del Sur, Bahía Blanca, Argentina; 
Piedra Grande SA, Trelew, Argentina; 
CNR-ISTEC, Faenza, Italy
ABSTRACT: Kaolin deposits of Patagonia (Argentina) were formed by "in situ" alteration of volcaniclastic rocks or by erosion, transportation, and deposition of residual clays in small basins. The mineralogy, geochemistry, grain size distribution, and specific surface area of natural and washed kaolins were studied in order to point out the relationships with the ceramic process. Primary kaolins are coarse-grained, kaolinite+quartz±halloysite, with a very low specific surface area. Sedimentary clays are either kaolinitic-smectitic and very fine-grained or kaolinitic with a coarser particle size distribution. An interdependence between mineralogy, chemistry, particle size distribution, texture, surface activity and ceramic behavior was found. Plasticity is strictly dependent on surface activity and expandable clay minerals. Slip rheology is affected by soluble salts, smectite, and tubular halloysite. Kaolinite-halloysite play an opposite role versus smectite-I/S in slip casting and tile pressing. Kaolinite and quartz are beneficial for drying behavior while expandable clay minerals increase drying sensitivity. Firing behaviour is mainly affected by minor components supplying fluxing oxides.
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

Domínguez, E.A.a , Iglesias, C.b , Dondi, M.c , Murray, H.H.d 
Geology, mineralogy, ceramic applications and genesis of La Espingarda kaolin deposit, Patagonia, Argentina
(2010) SME Annual Meeting and Exhibit 2010, pp. 525-528. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954222338&partnerID=40&md5=0ff0b1ed307ca448b446bc4c8cdbf38f
AFFILIATIONS: Univ. Nacional del Sur, Bahía Blanca, Argentina; 
Piedra Grande SA, Trelew, Argentina; 
CNR-ISTEC, Faenza, Italy; 
Indiana Univ., Bloomington, IN, United States
ABSTRACT: La Espingarda kaolin deposit was formed by "in situ" alteration of volcaniclastic rhyolitic rocks belonging to Jurassic Marifil Formation. Three volcanic lithofacies were identified: porphyric biotitic ignimbrites (PBI), a coarse lithic ignimbrite (ILG), a fluidal intrusive rhyolite (RFI), all kaolinized in different degrees. The alteration covers an ellipsoidal area of ∼20,000 m2, with its alteration decreasing downwards and disappearing at 8-12 m from the surface. The length to thickness ratio of alteration is 60:1. An erratic silicification was found as small zones (&lt;3 m2) of quartz stockwork. The mineralogy is kaolinite + quartz + feldspars + Fe-oxyhydroxides ± halloysite ± illite and interstratified I/S, although the relative proportions change in each rock type. Due to coarse grain size and high quartz content, natural kaolin is unsuitable for slip cast ceramics, unless beneficiated. Washed ILG kaolin has the best rheological properties and behavior in casting and drying for its mineralogy, particle size distribution, thin texture and surface activity, as well as a certain fusibility and firing kinetics. PBI and RFI kaolins, due to finer texture, smaller grain size, lower surface activity, and higher halloysite amount, have worse slip viscosity and thixotropy that are due also to soluble salts. For the same reason, they have good casting and drying properties, but their purity brings about higher softening temperatures and water absorption. Several parameters are used to discriminate between hypogene or supergene kaolinite genesis. The hydrothermal genesis is mainly sustained by fluid inclusion temperature (150-180°C) in quartz veinlets, while weathering is supported by deposit morphology, simple mineralogy, kaolinite stable isotopes (δ18O ‰ 18, 13; δD ‰ -59; -85) and paleoclimatic record. It is concluded that a weathering process formed the main alteration with some participation of steam-heated meteoric waters. Neither the contents of Au, Ag, As, Sb, Hg, nor drill data support the existence of any epithermal gold mineralization at the kaolinite bottom.
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

Barzoi, S.C., Seclaman, M.
Petrographic and geochemical interpretation of the Late Cretaceous volcaniclastic deposits from the Hateg Basin
(2010) Palaeogeography, Palaeoclimatology, Palaeoecology, 293 (3-4), pp. 306-318. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954958229&partnerID=40&md5=44b8d1d11c7bed8ba8fcacae35ded098
AFFILIATIONS: Department of Mineralogy, Faculty of Geology and Geophysics, University of Bucharest, 1, N. Balcescu Blvd., 1, RO-010041, Romania
ABSTRACT: The present paper provides new petrographic and geochemical insights into the tectonic and depositional environment of the Late Cretaceous volcaniclastic deposits from the Hateg Basin, in the South Carpathians. These deposits are widespread in the Rachitova-Stei unit, which is tectonically delimitated from the South Carpathians' geological background by strike-slip faults.The conducted petrographic studies have revealed that the volcaniclastic rocks from the Rachitova-Stei unit are mainly pyroclastic (i.e. coarse tuffs, tuff-breccia and tuffites), with a wide variety of volcanic pyroclastic fragments, most commonly including andesites (amphibole andesites, biotite-bearing-amphibole andesites, pyroxene-bearing-amphibole andesites, pyroxene-andesites), and less frequently latite-andesites, latites, rhyolites and dacites. The rhyolites are found only in the lower sequence of the Rachitova-Stei unit. The volcaniclastic deposits were altered by diagenetic processes. The celadonite is the most common diagenetic mineral formed in these rocks, whose presence indicates that the pyroclastic fragments have interacted with sea water.The high percentage of pyroclastic fragments with mainly angular forms and the rich-hornblende content evidence a highly explosive volcanism. The poorly-sorted pyroclastic assemblages with larger blocks and with little reworked pyroclastic material indicate a very short distance of transportation and a deposition relatively close to the explosion centre. The huge quantity of pyroclastic material from the Rachitova-Stei unit suggests that the volcanic explosion had a centre of considerable dimensions, but there is no evidence of such a volcano neither in the Hateg Basin nor anywhere else in the South Carpathians.The whole-rock geochemical composition and the immobile trace element signature from the pyroclastic fragments indicate an island arc depositional environment that was placed close to an active continental margin. In addition, the andesitic nature of the pyroclasts indicates that the volcaniclastic rocks were most probably derived from a magma generated by the subduction of an oceanic plate under a thin continental plate. The presence of the non-volcanic pyroclasts (i.e. granites, quartz-muscovite schists, muscovite quartzites, graphitic phyllites etc.), detached from the continental crust by explosion, confirms that the overriding plate is of continental material. The presence of the rhyolitic magma in the first stage of eruption also supports the continental nature of the overriding plate, the magma having resulted by the partial melting of the rocks from the continental crust.The petrographic and geochemical data have evidenced that the volcanism took place on a thin continental crust. However, this crust is not characteristic to the Getic Unit from the South Carpathians, which is commonly accepted to represent the basement of the Hateg Basin. Most probably, the volcanism was generated in another geotectonic context, respectively, in a continental island arc with a thin overriding crust, most likely situated at a lower latitude. The volcaniclastic units of the Hateg Basin were displaced and moved from this tectonic context to the present location by strike-slip movements. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Andesites;  Hateg Basin;  Pyroclastic rocks;  South Carpathians;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Do Campo, M.a , del Papa, C.b , Nieto, F.c , Hongn, F.b , Petrinovic, I.b 
Integrated analysis for constraining palaeoclimatic and volcanic influences on clay-mineral assemblages in orogenic basins (Palaeogene Andean foreland, Northwestern Argentina)
(2010) Sedimentary Geology, 228 (3-4), pp. 98-112. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954213782&partnerID=40&md5=1a54e0b488abe4724320ead59d45fe99
AFFILIATIONS: CONICET-U.B.A. Instituto de Geocronología y Geología Isotópica, Facultad de Ciencias Exactas y Naturales, Pabellón INGEIS, Ciudad Universitaria (1428) Buenos Aires, Argentina; 
CONICET-Universidad Nacional de Salta, Buenos Aires 177, 4400 Salta, Argentina; 
Departamento de Mineralogía y Petrología and I.A.C.T., Universidad de Granada-CSIC, Avda. Fuentenueva s/n, 18002-Granada, Spain
ABSTRACT: Variations in clay-mineral assemblages in ancient continental deposits are frequently used to reconstruct past climate changes. In active settings, volcanic events can supply highly labile volcaniclastic material, which can easily be transformed into smectite via diagenesis, which can produce a noticeable footprint in clay-mineral assemblages. Southern Central Andean foreland deposits are appropriate case studies to ascertain whether the climatic signal was preserved in the clay assemblages of their fine-grained sediments as tectonic uplift, volcanism, and sedimentation have been interacting since the Cretaceous. We have studied a 1400-m-thick coarsening-upward Palaeogene succession of the Tin Tin basin (northern Calchaquí Valley, Argentina), applying X-ray diffraction (XRD), electron microscopy, and detailed sedimentary facies analysis with the aim of comparing tendencies in the vertical fluctuations of clay minerals with evidence from sedimentological facies.Illite-muscovite plus smectite account for 78% to 100% of the clay minerals in the fine fraction, with kaolinite and chlorite in subordinate amounts. The vertical variation of sedimentary settings from an overbank/lacustrine domain to fluvial braided plains and an aeolian dune field suggests a gradual increase in aridity upsection. However, smectite abundances do not show a gradual decreasing trend compatible with progressively lower hydrolyzing conditions; their relative abundances vary widely throughout the section, depicting pulse-like, abrupt fluctuations. Despite the absence of field evidence for volcanic influence, several indications of volcanic and volcaniclastic material have been found under scanning electron microscopy (SEM) in levels with high smectite abundances from the middle to the top of the succession. They include quartz crystals showing embayments and skeletal forms, with smectite filling the voids, microcrystalline silica, as well as heulandite crystals in close association with authigenic smectite. The XRD analyses of these levels evidence well-crystallized smectite, which is characteristic of a volcaniclastic origin. Therefore, the increase in smectite abundance in these beds reflects a significant volcaniclastic contribution, which is also evidenced by a centimetre-thick ash layer topward in the sequence. The only smectite-rich level near the base of the Tin Tin section also contains well-crystallized smectite associated with heulandite, thus probably evidencing volcaniclastic input. We infer that most of the smectite in these sediments formed during early diagenesis, probably through the dissolution of labile tuffaceous material. Textural and morphological analysis by SEM is essential to determine whether clay-mineral assemblages could be interpreted in terms of palaeoclimate. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Clay minerals;  Foreland basins;  Northwest Argentina;  Smectite;  Volcaniclastic material
DOCUMENT TYPE: Article
SOURCE: Scopus

Breesch, L.a , Swennen, R.a , Vincent, B.b , Ellison, R.c , Dewever, B.a 
Dolomite cementation and recrystallisation of sedimentary breccias along the Musandam Platform margin (United Arab Emirates)
(2010) Journal of Geochemical Exploration, 106 (1-3), pp. 34-43. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953576841&partnerID=40&md5=40ffe6a35d2b31be5c3000c95eff4e78
AFFILIATIONS: Geologie, K.U.Leuven, Celestijnenlaan 200E, B-3001 Heverlee, Belgium; 
IFP, Géologie-Géochimie, 1-4 Avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France; 
British Geological Survey, Keyworth, Nottingham NG12 5GG, United Kingdom
ABSTRACT: Two main events of dolomite formation were identified along the southern border of the Late Jurassic Musandam carbonate platform of the UAE. The first dolomitisation phase (type 1) was restricted to specific stratigraphic layers in Jurassic platform limestones that were subsequently brecciated by mass flow and collapse processes on the platform margin. These dolomites are planar-s, have crystal sizes ranging from 5 to 25μm and exhibit an orange to pink and sometimes zoned red-yellow luminescence. This dolomite phase was formed shortly after deposition by fluids of marine or slightly modified marine composition.The second dolomite phase (type 2) mainly affected dolomite type 1 breccias by recrystallisation, dolomite cementation and replacement. Type 2 dolomites are planar-e and non-planar-c, with crystal sizes between 20 and 70μm. They have more elongated forms with purple luminescent to non-luminescent cores overgrown by pink to yellow luminescent rims. Stable isotope analyses show a covariant trend between δ18O and δ13C from marine (δ4.2 to δ1.8 and +0.8 to +2.1% VPDB respectively) towards depleted values (δ10.2 and δ8.9% VPDB respectively) This depletion is explained by recrystallisation during type 2 dolomitisation and it is interpreted in terms of high temperatures during precipitation and the incorporation of light carbon as hydrocarbons matured. Dolomite type 2 formation is thought to be the result of tectonically induced fluid flow which supplied hot magnesium-rich fluids.Two possible time scenarios for this fluid flow event are proposed: 1) during thrust emplacement of the tectonic nappes on top of the Musandam Platform in the Late Cretaceous. Volcaniclastic and basaltic rocks of the Hawasina Complex and the Oman-UAE ophiolites are a possible magmatic source for magnesium in this case; or 2) coinciding with the migration of hot, post-evaporative brines along the Hagab thrust, which acted as a fluid conduit during the Cenozoic orogeny. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Cementation;  Dolomite;  Fluid flow;  Musandam;  Oxygen isotopes;  Recrystallisation
DOCUMENT TYPE: Article
SOURCE: Scopus

Vicinanza, D.a , Guida, A.a , Ferrante, V.a , Ciavola, P.b 
Performance of a beach dewatering system-Chiaiolella Beach, Procida Island, Italy
(2010) Journal of Coastal Research, 26 (4), pp. 753-761. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954604053&partnerID=40&md5=5b8b271df3a5562b01defc5ff2826263
AFFILIATIONS: Seconda Universit di Napoli, Dipartimento di Ingegneria Civile, CIRIAM Via Roma 29, 81031 Aversa (Caserta), Italy; 
Universit di Ferrara, Dipartimento di Scienze della Terra, Via Saragat 1, 44100 Ferrara, Italy
ABSTRACT: Chiaiolella Beach is a 1.5-km-long pocket beach located on Procida Island (Italy). The beach is formed by medium sand generated by erosion of vulcanoclastic rocks that form cliffs around the island and at the backshore of the study site. A beach dewatering system was installed in April 2002 to provide a wider beach for users and to prevent cliff undercutting during storms. It has not been operative since December 2004, as local authorities decided to undertake cliff stabilization measures. Surveys carried out immediately before (October 2001) and 1 year after installation (October 2002) showed negligible volumetric change on the drained beach in Ciraccio (-0.52m3/m), the NNE sector of Chiaiolella Beach, whereas on the undrained control section there was an accumulation of 1.41m3/m. Since no long-term monitoring of beach profiles was available at the site previous to installation, to obtain an indication of the nearshore hydrodynamics and morphodynamics in absence of the drain, historical shoreline from high-resolution georeferenced aerial photography and numerical model were used. Overall, no evident positive effects of the dewatering system were confirmed, at least for mild wave energy levels. For higher wave energies, e.g., during a storm that occurred in December 2002, part of the beach (SSW sector, Ciracciello) had consistent volume losses and the dewatering system was not able to compensate them, as at some stage it was even damaged. This study points out the inadequacy of the dewatering system as coastal protection under high wave conditions. © Coastal Education &amp; Research Foundation 2010.
AUTHOR KEYWORDS: beach drainage;  Beach management system;  beach survey;  numerical modeling
DOCUMENT TYPE: Article
SOURCE: Scopus

Aliani, S.a , Bortoluzzi, G.b , Caramanna, G.c , Raffa, F.d 
Seawater dynamics and environmental settings after November 2002 gas eruption off Bottaro (Panarea, Aeolian Islands, Mediterranean Sea)
(2010) Continental Shelf Research, 30 (12), pp. 1338-1348. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955550137&partnerID=40&md5=32cb937ff2e93d6def094c6f0578bd63
AFFILIATIONS: CNR, ISMAR, Forte S. Teresa, 19036 Pozzuolo di Lerici, La Spezia, Italy; 
CNR, ISMAR, Via Gobetti 101, 40129 Bologna, Italy; 
Department of Chemical and Environmental Engineering, University Park, Nottingham, United Kingdom; 
CNR, IAMC, Spianata S. Ranieri 86, 98122 Messina, Italy
ABSTRACT: In November 2002 several gas bursts occurred at sea in the caldera within the islets eastward of Panarea (Aeolian Islands), with degassing of CO2 lasting several months. In a depression close to Bottaro Islet (PEG1) the gas flowed violently from the depth of ~14m to the surface producing a large plume of gas and fluids. The aims of this paper are to report on the morphological modifications, the water and gas fluxes, and the water dynamics and hydrological properties near the PEG1 site. Bathymetric surveys up to 2006 and divers' observations up to 2008 revealed that the sinkhole had been partially filled by sediments transported by currents or sliding from the rims. Depth reduced to ~12m and the shape of the depression was becoming similar to the others in the area, suggesting that explosive gas eruptions may have occurred in the past. The gas outflow generated a bubble plume that locally affected the water circulation. Different patterns in the dynamics of the water column were described using rotor current meters, ADCP, ROV and divers' observations, and high-resolution bathymetry. A divergence about 1m thick was generated by a surface vortex visible in December 2002 that was not found in September 2003 with reduced gas flow. A sub-surficial layer down to ~1-2m above bottom showed varying speed and directions possibly correlated to tides. A bottom layer of water ~1m thick flowed continuously toward the crater during both surveys. On the nearby sandy bottoms, sand dunes and 2/4mm size volcanoclastic gravels rolling toward the emitting area were found. The fluxes of water entering at the seafloor were calculated by current velocities, height of the bottom layer, and area of the degassing vent. The input water fluxes were found to be 4.2 and 0.2×108l/d, for December 2002 and September 2003. The total vertical output flux was also estimated; considering bubble sizes and voids, gas fluxes were 2.6 and 0.3×108l/d. These values are similar to the fluxes calculated by geochemical and gas sampling methods. CTD data from summer 2003 and spring 2004 recorded pH anomalies with values as low as 6.3 located on main emissions. The low pH water was also distributed laterally for dozens of meters on the bottom, depicting plumes and bottom layers of altered seawater over remarkable distances. The gas burst generated a plume similar to what is described for double core bubble plumes, where the velocity of seawater entering the system is proportional to the vertical gas flux. A new perspective to monitor vent activity is envisaged, and since measuring seawater is easier than measuring gas fluxes, a continuous and real time monitoring of hydrothermal activity could be designed. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Aeolian Islands;  Bubble plumes;  Gas eruption;  Panarea;  Seafloor morphology;  Shallow water vents
DOCUMENT TYPE: Article
SOURCE: Scopus

Stroberg, T.W.a , Manga, M.a , Dufek, J.b 
Heat transfer coefficients of natural volcanic clasts
(2010) Journal of Volcanology and Geothermal Research, 194 (4), pp. 214-219. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954539266&partnerID=40&md5=73ebb85824dcb3413016d6f47fc84215
AFFILIATIONS: Earth and Planetary Science, University of California, Berkeley CA 94720-4767, United States; 
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta GA, United States
ABSTRACT: Heat transfer coefficients used in numerical simulations of volcanic eruptions are typically borrowed from industrial settings where the coefficients are well determined for non-permeable, machined (spherical) materials. Volcanic clasts, in contrast, are permeable and have irregular shapes. We performed a series of laboratory experiments to determine heat transfer coefficients for natural volcanic particles. We measured the surface and interior temperatures during cooling at wind speeds ranging from 0 to 10m/s. We also measured the permeability and density of the particles. We find that the permeability of the particles has little effect on clast cooling. In the absence of any wind, heat loss occurs by free convection, and we find no relationship between the heat transfer coefficient and particle density. However, for non-zero Reynolds numbers (finite wind speed), the heat transfer coefficient decreases with increasing porosity. We obtain a correlation for the dimensionless heat loss, or Nusselt number, of the form Nu=2+aRe1/2Pr1/3 where a is a density dependent coefficient given by a=0.00022ρ+0.31, with ρ in kg/m3, and Re and Pr are the Reynolds number and Prandtl number, respectively. Compared with non-porous particles, heat transfer coefficients for natural pumice clasts are reduced by a factor of 2-3 for particles with similar Re. Numerical simulations show that this leads to an increase in depositional temperature by 50-90°C. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Heat transfer coefficients;  Permeability;  Pumice
DOCUMENT TYPE: Article
SOURCE: Scopus

Kadio, E., Coulibaly, Y., Allialy, M.E., Kouamelan, A.N., Pothin, K.B.K.
On the occurrence of gold mineralizations in southeastern Ivory Coast
(2010) Journal of African Earth Sciences, 57 (5), pp. 423-430. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953609128&partnerID=40&md5=fee478e17dfda2d01cbc39ecd65997fb
AFFILIATIONS: Laboratoire de Géologie du Socle et de Métallogénie, UFR STRM, Université de Cocody-Abidjan, 22 BP 582, Abidjan 22, Cote d'Ivoire
ABSTRACT: Gold mineralizations are known to occur in the Paleoproterozoic (Birimian) formations of the Aboisso area, southeastern Ivory Coast. These formations, which have been structured during the Eburnean orogeny, mainly consist of volcanic, volcaniclastic and sedimentary rocks intruded by granitic, basic and ultrabasic plutons. Exploration of these terranes has revealed numerous gold mineralizations, the most significant of which are located in the Aféma shear zone. Four distinct types of mineralizations can be distinguished based on the typology of the host rocks. These include mineralizations enclosed in highly silicified volcanic rocks (type 1), mineralizations closely related to intense silicification of metasedimentary rocks (type 2), mineralizations associated with silicified polygenic conglomerates (type 3), and mineralizations encountered in brecciated and silicified zones within a metadiorite sill (type 4). Gold is observed either as free gold, or in association with pyrite, arsenopyrite, sphalerite, chalcopyrite, ±pyrrhotite, ±galena, ±anatase, ±monazite, ±magnetite. Gold and the various sulfides are mostly of hydrothermal epigenetic origin. The fact that the gold mineralizations occurs in brecciated and silicified zones around granitoid intrusions clearly indicates that post-magmatic hydrothermal activity and tectonics exerted a major control during the mineralization process. © 2009 Elsevier Ltd.
AUTHOR KEYWORDS: Aféma (Ivory Coast);  Birimian;  Gold;  Hydrothermalism;  Shear zone;  Tectonics
DOCUMENT TYPE: Article
SOURCE: Scopus

Cluzel, D.a  b , Adams, C.J.a  b  c , Meffre, S.a  b  d , Campbell, H.a  b  e , Maurizot, P.a  b  f 
Discovery of early cretaceous rocks in New Caledonia: New Geochemical and U-Pb zircon age constraints on the transition from subduction to marginal breakup in the Southwest Pacific
(2010) Journal of Geology, 118 (4), pp. 381-397. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955690889&partnerID=40&md5=4f324cf6d28aafe2e19ad6616a7ac3ec
AFFILIATIONS: Pǒle Pluridisciplinaire de la Matière et de l'Environnement, EA 3325, Université de la Nouvelle-Calédonie, BP R4, 98851 Noumea Cedex, New Caledonia; 
Institut des Sciences de la Terre d'Orléans, Unité Mixte de Recherche 6113, Centre National de la Recherche/Université d'Orléans, 1A rue de la Fé rollerie, 45071 Orléans Cedex 2, France; 
Geological and Nuclear Sciences, Private Bag 1930, Dunedin, New Zealand; 
Australian Research Council Centre of Excellence in OreDeposits, University of Tasmania, Hobart Campus, Private Bag 79, Hobart, TAS 7001, Australia; 
Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand; 
Bureau de Recherches Géologiques et Minières, Direction de l'Industrie, Des Mines et de l'Energie, B.P. 465, 98845 Nouméa, New Caledonia
ABSTRACT: New U-Pb dating of detrital zircon and geochemical features of Permian-Mesozoic arc-derived volcanic rocks and volcaniclastic turbidites (graywackes), when compared with those of the volcanic rocks associated with unconformable Late Cretaceous shallow-water sediments, reveal that subduction in New Caledonia, once thought to be extinct in the Late Jurassic (ca. 150 Ma), was still active at least from ca. 130 to 95 Ma. The accumulation of volcanic arcderived sediments during the late Early Cretaceous suggests that, as in New Zealand, active-margin activity went on for a short time in spite of the assumed subduction jamming by the Hikurangi Plateau at ca. 100 Ma. Meanwhile, the rift-related magmatic activity that preceded the marginal breakup migrated eastward from ca. 130 Ma (130-95 Ma) in eastern Australia, to 110 Ma (110-82 Ma) in New Zealand, and, finally, to ca. 89 Ma (89-83 Ma) in New Caledonia and generated large volumes of silicic magma. In contrast, marginal basins opened synchronously at ca. 83 Ma when the stretched continental crust finally broke out. In general, intraplate and volcanic arc signatures coexisted in Cretaceous syn-rift magmas. Therefore, the Australian marginal breakup appears to be the final effect of continuous southward unzipping of Gondwana that interfered with the subduction-modified mantle wedge of the Mesozoic active margin. The occurrence of lateral flow of the upper asthenospheric mantle due to the rapidly eastwardmigrating Australian plate margin possibly prevented the formation of a volcanic arc at the eastern end of the system. © 2010 by The University of Chicago. All rights reserved.
DOCUMENT TYPE: Article
SOURCE: Scopus

Dunning, G., Indares, A.
New insights on the 1.7-1.0 Ga crustal evolution of the central Grenville Province from the Manicouagan - Baie Comeau transect
(2010) Precambrian Research, 180 (3-4), pp. 204-226. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953649412&partnerID=40&md5=7fe8b41ea58155e3379e2b05fd8eaee3
AFFILIATIONS: Department of Earth Sciences, Memorial University of Newfoundland, St. John's, A1B 3X5 NL, Canada
ABSTRACT: Integrated field relationships and U-Pb geochronology of rocks exposed along the southern part of the Manicouagan reservoir (central Grenville Province, Quebec) provide insights into protolith formation and thermal events that range in age from ca. 1.7 to 0.9 Ga and share common features with the rest of the Grenville Province and beyond. From presently lower to higher structural levels, main findings include the recognition of: (a) ca. 1.70-1.75 Ga granitic magmatism and metamorphism in the southern part of the parautochthonous Gagnon terrane, correlative in age with late stages of magmatism in the Makkovik Orogen to the northeast; (b) a ca. 1.69 gabbro-anorthosite suite (Island domain) which is inferred to represent the southwesternmost exposure of Labradorian crust in the central Grenville Province; (c) a 1.4 Ga volcaniclastic sequence and associated plutonic rocks (Canyon domain), which based on lithological association and age, is inferred to represent the NNE extension of the Montauban island arc; and (d) a ca. 1.2 Ga bimodal felsic-mafic volcanic to intermediate volcaniclastic sequence (Banded complex), inferred to have originated in an intra-continental rift system, contemporaneously with the Composite Arc Belt (southwestern Grenville Province) and with widespread extensional magmatism elsewhere in the Canadian Shield. In addition, 1.3 Ga granitoid plutons are documented to intrude Labradorian units at the NW boundary of Canyon domain. The significance of these plutons is ambiguous, as they may represent either stitching plutons, marking the accretion of the 1.4 Ga Canyon domain to the Laurentian margin, or the first stage in the development of the ca. 1.2 Ga continental rift system. The hinterland units (Island domain, Canyon domain and Banded complex) were metamorphosed under medium-pressure granulite facies conditions during the culmination of the Grenvillian orogeny between 1.08 and 1.04 Ga. This metamorphism was accompanied by ca. 1.07 Ga A-type granitic magmatism in Canyon domain. In addition, locally abundant ca. 0.98 Ga late-tectonic felsic pegmatite and ultrapotassic dykes occur in Canyon domain. This event is coeval with titanite ages documented in a wide range of units. The data on the Grenvillian evolution suggest mantle-derived magmatism and associated metamorphism in the hinterland during both the culmination and the waning stages of the Grenvillian orogeny. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Grenville Province;  Magmatism;  Metamorphism;  U-Pb geochronology
DOCUMENT TYPE: Article
SOURCE: Scopus

Genç, Ş.C.a , Tüysüz, O.b 
Tectonic setting of the Jurassic bimodal magmatism in the Sakarya Zone (Central and Western Pontides), Northern Turkey: A geochemical and isotopic approach
(2010) Lithos, 118 (1-2), pp. 95-111. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955689075&partnerID=40&md5=7322949df1e2b9f28b86d6a2aa16f2f9
AFFILIATIONS: Istanbul Technical University, Faculty of Mines, Dept. of Geological Engineering, 34469 Maslak, Istanbul, Turkey; 
Istanbul Technical University, Eurasia Institute of Earth Sciences, 34469 Maslak, Istanbul, Turkey
ABSTRACT: The Lower to Middle Jurassic Mudurnu formation of the Sakarya Zone (Northern Turkey) was deposited in an extensional basin. This unit crops out along the southern Pontide range and consists of marine sedimentary rocks including debris flows, lignite-bearing clastic rocks and Ammonitico Rosso horizons alternating with mafic and felsic volcanic and volcaniclastic rocks. Magmatic rocks of the Mudurnu formation comprise two compositionally different groups; 1) a mafic group including diabase-microgabbro-basaltic lavas and their pyroclastic equivalents, and 2) a felsic group including granite porphyries and felsic pyroclastic rocks. All the magmatic members of the Mudurnu formation are subalkaline and display a calc-alkaline affinity. They are bimodal, with a significant silica gap between the mafic and felsic members with the exception of a few samples. These magmatic rocks display enrichment in LILE and depletion in Nb, Ta, P and Ti, implying a subduction-related magmatic signature. Melting modelling for the mafic rocks indicates that they originated possibly from subcontinental lithospheric mantle (SCLM) composed of spinel lherzolite. εNd(i) values (+. 1.5 to +. 4.3) imply that the mafic volcanic and hypabyssal rocks were possibly derived from a time-integrated LREE-depleted mantle source. The initial Sr and Nd isotope values, and εNd(i) of the felsic hypabyssal rocks are comparable to the mafic ones. The isotope data point to a genetic relationship between the felsic and mafic members. Results obtained from the geochemical modelling of incompatible versus compatible trace elements show that the felsic rocks were derived from the mafic melts by fractional crystallization (FC) process. In the light of their regional geological setting and these geochemical characteristics, we propose that the magmatic rocks of the Mudurnu formation formed in an extensional basin situated on an active and/or just ended subduction zone during the Jurassic period. The Mudurnu formation is a good example of extensional magmatism derived from a depleted mantle source that displayed subduction signatures and that was modified by fluids from a long-lived subduction event. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Bimodal magmatism;  Geochemistry;  Jurassic;  Sakarya Zone;  Sr-Nd isotope;  Subduction-signature
DOCUMENT TYPE: Article
SOURCE: Scopus

Du, X.a  b , Xie, X.a , Lu, Y.a , Zhang, L.a , Zhang, C.a 
Hydrogeochemistry of formation water in relation to overpressures and fluid flow in the Qikou Depression of the Bohai bay basin, China
(2010) Journal of Geochemical Exploration, 106 (1-3), pp. 77-83. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953552831&partnerID=40&md5=1d22c41b36a582d6e6d68ecb874c3702
AFFILIATIONS: Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan, 430074, China; 
Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
ABSTRACT: The Qikou Depression is the largest hydrocarbon bearing depression in the western part of the Bohai bay basin, dominated by fan delta and lacustrine strata with volcanic and volcaniclastic rocks. In this study, the formation pressures and hydrochemistry of the formation water in the Qikou depression are investigated. It is found that a significant overpressure occurs in the Dongying (Ed) Formation and the first member (Es1), the second member (Es2), the third member (Es3) of the Shahejie Formation. The pressure coefficients commonly range from 1.2 to 1.6 with the highest pressure coefficient being 1.7. The analysis of hydrochemistry data shows that the whole depression is dominated by NaHCO3 water type. The concentration of total dissolved solid (TDS) ranges from 2.13 to 53.16g/L and shows a distinct vertical variation of salinity and ion ratios. High salinity water (TDS&gt;10g/L) occurs below a depth of 2500m, which coincides with the presence of the overpressured system. However, the increasing trend of TDS is diminished below 3500m because the generation of organic acids in Qikou Depression is inhibited in the presence of overpressure. The analysis of the relationship among different ions indicates that the present-day characteristics of the formation water result from the albitization of feldspar and the dissolution of sodium-rich silicate minerals and halite in the different hydrochemical and pressure systems. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Fluid flow;  Hydrogeochemistry;  Overpressure;  Qikou Depression;  Water-rock interaction
DOCUMENT TYPE: Article
SOURCE: Scopus

Khalaf, E.E.D.A.H.
Stratigraphy, facies architecture, and palaeoenvironment of Neoproterozoic volcanics and volcaniclastic deposits in Fatira area, Central Eastern Desert, Egypt
Journal of African Earth Sciences, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953235926&partnerID=40&md5=042becb73cdac50928f1db4d58a8425e
AFFILIATIONS: Cairo University, Faculty of Science, Geology Department, Egypt
ABSTRACT: Fatira area in the Central Eastern Desert, Egypt, is a composite terrane consisting of Neoproterozoic volcanics and sediments laid down in submarine to subaerial environment, intruded by voluminous old to young granitic rocks. The various lithofacies of the study area can be grouped in three distinct lithostratigraphic sequences, which are described here in stratigraphic order, from base to top as the Fatira El Beida, Fatira El Zarqa and Gabal Fatira sequences. Each depositional sequence, is intimately related to volcanic activity separated by time intervals of volcanic inactivity, such as marked hiatuses, reworked volcaniclasts, and or turbidite sedimentation. Four submarine facies groups have been recognized within the oldest, folded eruption sequence of Fatira El Beida. The southern part of the study area is occupied by sheet lava (SL), pillow lavas (PL), pillow breccias (PB), and overlying Bouma turbiditic volcaniclastites (VC). The four facies groups of Fatira El Beida sequence occur in a predictable upward-deepening succession, essentially from base to top, an SL-PL-PB-VC stacking pattern. The coeval tholeiitic mafic and felsic volcaniclastic rocks of this sequence indicate an extensional back-arc tectonic setting. The El Beida depositional sequence appears to fit a submarine-fan and slope-apron environment in an intra-arc site. The Fatira El Zarqa sequence involves a large volume of subaerial calc-alkaline intermediate to felsic volcanics and an unconformably overlying siliciclastic succession comprising clast-supported conglomerates (Gm), massive sandstone sheet floods (Sm) and mudstones (FI), together with a lateritic argillite paleosol (P) top formed in an alluvial-fan system. The youngest rock of Gabal Fatira sequence comprises anorogenic trachydacites and rhyolites with locally emergent domes associated with autobrecciation and sill-dyke rock swarms that could be interpreted as feeders and subvolcanic intrusions. Unconformity and lithofacies assemblages define seven events and three unconformity-bounded tectonic stages that record uplift-subsidence cycles in the study area. A proximal-distal relationship has been established within the depositional products, based on the relative dominance of erosional and depositional features. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Central Eastern Desert, Egypt;  Fatira area;  Geotectonic setting;  Neoproterozoic;  Subaqueous vs. subaerial eruption;  Volcanic lithofacies associations
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Zoheir, B.A.a , Akawy, A.b 
Genesis of the Abu Marawat gold deposit, central Eastern Desert of Egypt
(2010) Journal of African Earth Sciences, 57 (4), pp. 306-320. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950863529&partnerID=40&md5=c2ab7afb4d32136d9ceef589fdb32408
AFFILIATIONS: Department of Geology, Faculty of Science, Benha University, 13518 Benha, Egypt; 
Department of Geology, Faculty of Science, South Valley University, Qena, Egypt
ABSTRACT: Gold mineralisation at the Abu Marawat mine, central Eastern Desert of Egypt, is related to a system of massive and sheared, milky quartz veins cutting a sequence of Neoproterozoic island arc metavolcanic/volcaniclastic rocks and related banded iron formation (BIF). Sulphide-bearing quartz veins and related hydrothermal breccia bodies display a range of textures including sheared, boudinaged and recrystallised quartz, open space filling and microbreccia. These variable textures imply a complex history of crack-seal mechanism characterising the relation between mineral deposition and a major N-S-trending shear zone, during a late brittle-ductile deformation event which affected the area at about 550 Ma. Gold-base metal mineralisation is associated with brecciation and fracturing of the iron ore bands, close to silicified shears and related quartz veins. The auriferous quartz lodes are characterised by the occurrence of visible pyrite-chalcopyrite ± pyrrhotite ± sphalerite ± galena mineralisation. Gold is refractory in pyrite and chalcopyrite, but rare visible gold/electrum and telluride specks were observed in a few samples. Hydrothermal alteration includes pervasive silicification, pyritisation, sericitisation, carbonatisation confined to a delicate set of veins and altered shears, and a more widespread propylitic alteration assemblage (quartz + chlorite + pyrite + calcite ± epidote). Fluid inclusion petrography and microthermometric studies suggest heterogeneous trapping of a low-salinity (1.4-6.7 wt.% eq. NaCl) aqueous solution and a carbonic fluid. Evidence for fluid immiscibility during ore formation includes variable liquid/vapour ratios in inclusions along individual trails and bulk inclusion homogenisation into liquid and occasionally to vapour at comparable temperatures. The trapping conditions of intragranular aqueous-carbonic inclusions approximate 264-378 °C at 700-1300 bar. Similar temperature estimates have been obtained from Al-in-chlorite geothermometry of chlorite associated with sulphides in the mineralised quartz veins. Fracturing enhanced fluid circulation through the wallrock and related BIF, allowing reaction of the S-bearing ore fluid with iron oxides. This caused pyrite formation and concomitant Au precipitation, enhanced by fluid immiscibility as H2S partitioned preferentially into the carbonic phase. The ore fluids may have originated from granitoid intrusions (likely the post-Hammamat felsites, whereas gold and base metals might have been leached from the Abu Marawat basic metavolcanics. © 2009 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Abu Marawat;  BIF;  Eastern Desert of Egypt;  Fluid inclusions;  Hydrothermal alteration;  Shear zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Ufimtsev, G.F.
Geomorphological features of the Peruvian Andes
(2010) Geography and Natural Resources, 31 (2), pp. 183-191. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954191015&partnerID=40&md5=12e0b00ea0970f302d5d83ec41c8990a
AFFILIATIONS: Institute of the Earth's Crust SB RAS, Irkutsk, Russian Federation
ABSTRACT: The characteristic features of the relief and morphogenesis of the Peruvian Andes are described, which represent an expanded portion of a young mountain belt with an intrinsic array of geomorphological paradoxes and disturbances in altitudinal zonality of the morphogenesis. This study identified the main types of river valleys and alpine lake depressions, valley and piedmont pediments, surfaces of volcanic accumulation, shore terraces, and varied manifestations of the aeolian morphogenesis. The main kinds of natural monuments and morphological landscapes are characterized. © 2010.
AUTHOR KEYWORDS: Aeolian processes;  Altitudinal zonality;  Geographical zonality;  Morphogenesis;  Relief;  Shore terraces
DOCUMENT TYPE: Article
SOURCE: Scopus

van Leeuwen, T.M.a , Susanto, E.S.b , Maryanto, S.b , Hadiwisastra, S.c , Sudijonob , Muhardjod , Prihardjob 
Tectonostratigraphic evolution of Cenozoic marginal basin and continental margin successions in the Bone Mountains, Southwest Sulawesi, Indonesia
(2010) Journal of Asian Earth Sciences, 38 (6), pp. 233-254. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952093932&partnerID=40&md5=f7c42a4e980b053d4664c9444010b96f
AFFILIATIONS: Jl. H. Naim IIIB No. 8, Jakarta 12150, Indonesia; 
Geological Development and Research Centre, Jl. P. Diponegoro No. 57, Bandung, Indonesia; 
Lembaga Geoteknologi, LIPI, Jl. Cisitu Sangkuriang No. 21, Bandung, Indonesia; 
PT Rio Tinto Exploration, 15th Floor Menara Anugrah Kantor, Jakarta 12950, Indonesia
ABSTRACT: The Bone Mountains, located in Southwest Sulawesi along the SE margin of Sundaland, are composed of Oligocene to possibly lower Miocene marginal basin successions (Bone Group) that are juxtaposed against continental margin assemblages of Eocene-Miocene age (Salokalupang Group). Three distinct units make up the latter: (i) Middle-Upper Eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part (Matajang Formation), reflecting a period of arc volcanism and carbonate development along the Sundaland margin; (ii) a well-bedded series of Oligocene calc-arenites (Karopa Formation), deposited in a passive margin environment following cessation of volcanic activity, and (iii) a series of Lower-Middle Miocene sedimentary rocks, in part turbiditic, which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity (Baco Formation), formed in an extensional regime without subduction.The Bone Group consists of MORB-like volcanics, showing weak to moderate subduction signatures (Kalamiseng Formation), and a series of interbedded hemipelagic mudstones and volcanics (Deko Formation). The Deko volcanics are in part subduction-related and in part formed from melting of a basaltic precursor in the overriding crust. We postulate that the Bone Group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west (Sundaland) and by a newly initiated westerly-dipping subduction zone on its eastern side.Around 14-13. Ma an extensional tectonic event began in SW Sulawesi, characterized by widespread block-faulting and the onset of potassic volcanism. It reached its peak about 1. Ma year later with the juxtaposition of the Bone Group against the Salokalupang Group along a major strike-slip fault (Walanae Fault Zone). The latter group was sliced up in variously-sized fragments, tilted and locally folded. Potassic volcanism continued up to the end of the Pliocene, and locally into the Quaternary. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Continental margin;  Geochemistry;  Marginal basin;  Paleontological dating;  Southwest Sulawesi;  Stratigraphy
DOCUMENT TYPE: Article
SOURCE: Scopus

Komorowski, J.-C.a  b , Legendre, Y.a  b , Christopher, T.b , Bernstein, M.c , Stewart, R.b  d , Joseph, E.b  d , Fournier, N.b  d  e , Chardot, L.b  f , Finizola, A.a  b  g , Wadge, G.h , Syers, R.b , Williams, C.b , Bass, V.b 
Insights into processes and deposits of hazardous vulcanian explosions at Soufrière Hills Volcano during 2008 and 2009 (Montserrat, West Indies)
(2010) Geophysical Research Letters, 37 (11), art. no. L00E19, . Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953576221&partnerID=40&md5=a0dbf47fc856e5cf6001a89f120b4683
AFFILIATIONS: Institut de Physique du Globe de Paris, UMR 7154, CNRS, place Jussieu, F-75252 Paris Cedex 05, France; 
Montserrat Volcano Observatory, Flemmings, Salem, MSR, Trinidad and Tobago; 
Center for Geohazards, University at Buffalo, SUNY, New York, NY 14260, United States; 
Seismic Research Centre, University of the West Indies, Saint Augustine, Trinidad and Tobago; 
Wairakei Research Centre, GNS Science, 114 Karetoto Rd., Taupo 3377, New Zealand; 
Ecole et Observatoire des Sciences de la Terre, 5, rue Rene Descartes, F-67084 Strasbourg Cedex, France; 
Laboratoire GoSciences Runion, Universit de la Runion, IPGP, Saint-Denis, France; 
Environmental Systems Science Centre, NCEO, University of Reading, 3 Earley Gate, Reading RG6 6AL, United Kingdom
ABSTRACT: During the Soufrire Hills eruption, vulcanian explosions have generally occurred 1) in episodic cycles; 2) isolated during pauses in extrusion, and 3) after major collapses of the dome. In a different eruptive context, significant vulcanian explosions occurred on 29 July 2008, 3 December 2008, and 3 January 2009. Deposits are pumiceous except for the 3 December event. We reconstructed the dispersal pattern of the deposits and their textural characteristics to evaluate erupted volume and vesicularity of the magma at fragmentation. We discuss the implications of these explosions in terms of eruptive processes and chronology, and the hazards posed by their sudden and often unheralded occurrence. We suggest that overpressurization of the conduit can develop over time-scales of months to weeks by a process of self-sealing of conduit walls and/or the cooling dome by silica polymorphs. This work provides new insights for understanding the generation of hazardous vulcanian explosions at andesitic volcanoes. Copyright © 2010 by the American Geophysical Union.
DOCUMENT TYPE: Article
SOURCE: Scopus

Eliwa, H.a , Breitkreuz, C.b , Khalaf, I.a , Gameel, K.E.a  b 
Depositional styles of Early Ediacaran terrestrial volcanosedimentary succession in Gebel El Urf area, North Eastern Desert, Egypt
(2010) Journal of African Earth Sciences, 57 (4), pp. 328-344. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950862819&partnerID=40&md5=5f1afef1efd383ee3871cf040ca027bc
AFFILIATIONS: Geology Department, Faculty of Science, Minufiya University, Sheben El Kom, Egypt; 
Geological Institute, Technische Universität Bergakademie Freiberg, Bernhard-von-Cotta-Str. 2, 09599 Freiberg, Germany
ABSTRACT: Located 100 km northwest of Hurghada, the volcanosedimentary successions of Gebel El Urf is exposed between latitude 27° 45′ 30″ and 27° 51′ 00″ N and longitude 32° 49′ 00″ and 32° 59′ 00″ E. The volcanosedimentary successions of Gebel El Urf crop out in an area dominated by different Late Proterozoic plutonic complexes. Both, erosional and intrusive contacts with different granitoid units have been identified. Two SHRIMP ages have been obtained from crystal-rich and lithic-poor ignimbrites yielding 615 ± 4 and 616.0 ± 5.4 Ma placing the evolution of the inter-montane basins, described here, into the Early Ediacaran. In the Gebel El Urf area, a southeastward dipping succession (Gebel El Urf Succession, GUS) of ca. 2000 m thickness rests on coarse-grained granite with an erosional unconformity. Another succession present in the area (Wadi Kefri Succession, WKS) represents volcanogenic sediments which exhibit degrees of metamorphic overprint. In places, it is presumed to be older than GUS. For the GUS, 14 lithofacies types have been differentiated and grouped to seven lithofacies associations. Subdivided into four depositional phases, GUS starts with a thick, massive and clast-supported conglomerate of alluvial fan facies (well-rounded clasts up to 100 cm). GUS continues with pelitic to sandy-turbiditic lacustrine and sandy braided river deposits with occasional volcanic glassy fragments (now illite) (Phase 2). The upper half of the GUS is dominated by volcanic deposits, starting with a 50 m thick package of alternating ignimbrites and synvolcanic sedimentary mass flow deposits, the latter related to phreatomagmatic vents (Phase 3). A thick succession of welded to non-welded ignimbrites follows, with one 20 m intercalation of coarse well-rounded conglomerates (Phase 4). Numerous SiO2-rich and - poor dykes and sills emplaced into GUS. The GUS development displays a cycle from high to low energy sedimentation and back, under humid climatic conditions. Phase 2 was characterized by extension and down faulting of basin shoulders. Tectonic activity presumably also led to damming of the river creating a sweat water lake. Volcanism commenced with small vents during Phase 2 and terminated with voluminous eruptions in Phase 4. © 2009 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Dokhan Volcanics;  Ediacaran;  Egypt;  Facies analysis;  Gebel El Urf;  Hammamat Sediments
DOCUMENT TYPE: Article
SOURCE: Scopus

Ciaranfi, N.a , Lirer, F.b , Lirer, L.c , Lourens, L.J.d , Maiorano, P.a , Marino, M.a , Petrosino, P.c , Sprovieri, M.b , Stefanelli, S.a , Brilli, M.e , Girone, A.a , Joannin, S.f , Pelosi, N.b , Vallefuoco, M.b 
Integrated stratigraphy and astronomical tuning of lower-middle Pleistocene Montalbano Jonico section (southern Italy)
(2010) Quaternary International, 219 (1-2), pp. 109-120. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952952179&partnerID=40&md5=d124b8f4317bd7d370aa51632a94579d
AFFILIATIONS: Dipartimento di Geologia e Geofisica, Università di Bari, Via E. Orabona 4, 70125 Bari, Italy; 
Istituto per l'Ambiente Marino Costiero (IAMC) Sede Napoli - CNR, Calata Porta di Massa, Interno Porto di Napoli, 80133, Napoli, Italy; 
Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, L.go San Marcellino 10, 80138 Napoli, Italy; 
Faculty of Geosciences, Department of Earth Sciences, Utrecht University, Utrecht, Netherlands; 
Istituto di Geologia Ambientale e Geoingegneria (IGAG)-CNR, Via Bolognola 7, 00138 Rome, Italy; 
UMR 5125 PEPS, CNRS, France; Université Lyon 1, Campus de La Doua, Bâtiment Géode, 69622 Villeurbanne Cedex, France
ABSTRACT: Astronomical calibration of the lower-middle Pleistocene Montalbano Jonico section located in the Lucania Basin (Southern Italy) is presented. Previous papers widely discussed the integrated stratigraphy (calcareous nannofossils, sapropel stratigraphy, benthic and planktonic oxygen stable isotopes) and the paleoenvironmental features of this section and its potential suitability for the selection of the Middle Pleistocene Global Stratotype Section and Point (GSSP). In this study, new planktonic δ18O data, additional biostratigraphical constraints and new tephrochronology on volcaniclastic layers occurring within the studied record are reported. The new chronostratigraphic framework provides a robust base for correlation of the oxygen isotope stratigraphy for the Montalbano Jonico section with the glacial and interglacial fluctuations of the Oceanic and Mediterranean δ18O reference deep-sea records. Specifically, the lower part of the Montalbano Jonico section (Interval A) provides correlation of the planktonic and benthic δ18O cycles to Marine Isotope Stage (MIS) 36 to MIS 23. Interval A includes a distinct peak of left-coiled neogloboquadrinids, the Globoratalia crassaformis influx, the First Occurrence of Gephyrocapsa omega, and the First Common Occurrence and Last Common Occurrence of Reticulofenestra asanoi. These stratigraphical constraints support the tuning of five sapropel layers included in this part of the section to insolation cycles i-112, i-104, i-102, i-90 and i-86. The upper part of the section (Interval B), which includes the temporary disappearance (td2) of G. omega and tephra layer V5, Ar/Ar age dated at 719.5±12.6ka, is consistent with identification of MIS 22 to MIS 16 in the planktonic δ18O pattern. The δ18O time series of the whole section was reconstructed using the midpoints of individual sapropels and their correlative precession minima, visual comparison of the δ18O pattern with the record available at the Mediterranean ODP Site 975, and, in the upper part of the section, the Ar/Ar age of tephra V5. The developed astronomical tuning revealed that the Montalbano Jonico section covers an interval from 1240ka to 645ka. A significant change in sedimentation rate occurs between Intervals A (0.53m/ky) and Interval B (0.91m/ky) at about 870ka and is consistent with a sea-level drop from a bathyal to a circalittoral environment. Bioevents recognised in the Montalbano Jonico section have been dated according to the astronomical calibration, and age assignments of tephra V1-V4 and V6-V9 are also proposed. The Montalbano Jonico section fills the gap between the top of the Vrica section and the base of the Ionian informal Middle Pleistocene stage, and represents a Mediterranean reference section for the Mid-Pleistocene transition. © 2009 Elsevier Ltd and INQUA.
DOCUMENT TYPE: Article
SOURCE: Scopus

Terekhov, E.P., Mozherovsky, A.V., Gorovaya, M.T., Tsoy, I.B., Vashchenkova, N.G.
Composition of the rocks of the Kotikovo Group and the main stages in the Late Cretaceous-Paleogene evolution of the Terpeniya Peninsula, Sakhalin Island
(2010) Russian Journal of Pacific Geology, 4 (3), pp. 260-273. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954080476&partnerID=40&md5=f8f865c50700355141cf5f6059866766
AFFILIATIONS: Il'ichev Pacific Oceanological Institute, Far East Branch, Russian Academy of Sciences, ul. Baltiiskaya 43, Vladivostok, 690041, Russian Federation
ABSTRACT: This paper reports and discusses the composition of the rocks of the Kotikovo Group (the Uchir, Zaslonovskaya, Turovskay, and Ol'don formations) of the Terpeniya Peninsula (East Sakhalin). It is suggested that the Cenozoic deposits unconformably overlay the Maastrichtian-Danian rocks with basal conglomerates at the base. Two main stages were distinguished in the Late Cretaceous-Paleogene evolution of this area on the basis of our study. The first stage was responsible for the formation of the Maastrichtian-Danian volcaniclastic and volcanogenic-sedimentary rocks of the Uchir Group, while the second stage produced the Paleocene-Eocene sedimentary rocks of the Zaslonovskaya, Turovskaya, and Ol'don formations. The end of the first stage (at the boundary of the Uchir and Zaslonovskaya formations) was marked by a change in the tectonic regime. This was expressed in the weakening of the volcanic activity, the uplift of the territory, and the exposure of new provenances to erosion. During the second, Early Paleogene stage, the area of the East Sakhalin Mountains, the Terpeniya Peninsula, and the submarine Terpeniya Ridge represented a shallow-water marine sedimentary basin representing the western flank of the Cenozoic Pogranichnyi Basin. The formation of the anticlinal East Sakhalin Mountains-Terpeniya Peninsula-submarine Terpeniya Ridge structure occurred during the Late Cenozoic period of the East Sakhalin evolution. © 2010 Pleiades Publishing, Ltd.
AUTHOR KEYWORDS: Composition;  East Sakhalin anticlinorium;  Eocene;  Key words;  Kotikovo Group;  Paleocene;  Radiolarians;  Sakhalin Island;  Spore and pollen flora;  Terpeniya Peninsula;  Upper Cretaceous
DOCUMENT TYPE: Article
SOURCE: Scopus

Le Gall, B.a , Daoud, M.A.b , Maury, R.C.a , Rolet, J.a , Guillou, H.c , Sue, C.a 
Magma-driven antiform structures in the Afar rift: The Ali Sabieh range, Djibouti
(2010) Journal of Structural Geology, 32 (6), pp. 843-854. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955922785&partnerID=40&md5=1c0f675ff05b6d87fc44494baa9423d9
AFFILIATIONS: Université Européenne de Bretagne, Université de Brest, CNRS; UMR 6538 Domaines Océaniques, Place N. Copernic, 29280 Plouzané, France; 
Institut des Sciences de la Terre, Centre d'Etudes et de Recherches de Djibouti, B.P. 486, Djibouti Ville, Djibouti; 
UMR 1572, LSCE/CEA-CNRS, Domaine du CNRS, 12 avenue de la Terrasse, 91118 Gif-sur-Yvette, France
ABSTRACT: The Ali Sabieh Range, SE Afar, is an antiform involving Mesozoic sedimentary rocks and synrift volcanics. Previous studies have postulated a tectonic origin for this structure, in either a contractional or extensional regime. New stratigraphic, mapping and structural data demonstrate that large-scale doming took place at an early stage of rifting, in response to a mafic laccolithic intrusion dated between 28 and 20 Ma from new K-Ar age determinations. Our 'laccolith' model is chiefly supported by: (i) the geometry of the intrusion roof, (ii) the recognition of roof pendants in its axial part, and (iii) the mapping relationships between the intrusion, the associated dyke-sill network, and the upper volcanic/volcaniclastic sequences. The laccolith is assumed to have inflated with time, and to have upwardly bent its sedimentary roof rocks. From the architecture of the ~1 km-thick Mesozoic overburden sequences, ca. 2 km of roof lifting are assumed to have occurred, probably in association with reactivated transverse discontinuities. Computed paleostress tensors indicate that the minimum principal stress axis is consistently horizontal and oriented E-W, with a dominance of extensional versus strike-slip regimes. The Ali Sabieh laccolith is the first regional-scale magma-driven antiform structure reported so far in the Afro-Arabian rift system. © 2010 Elsevier Ltd.
AUTHOR KEYWORDS: Afar rift;  Ali sabieh range;  Antiform;  Djibouti;  Extension;  Mafic laccolith;  Oligo-Miocene
DOCUMENT TYPE: Article
SOURCE: Scopus

Winter, L.S.a , Tosdal, R.M.a , Mortensen, J.K.b , Franklin, J.M.c  d 
Volcanic stratigraphy and geochronology of the cretaceous Lancones Basin, Northwestern Peru: Position and Timing of Giant VMS Deposits
(2010) Economic Geology, 105 (4), pp. 713-742. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77958522329&partnerID=40&md5=2aefe6e10af95661e59a586e7786fe36
AFFILIATIONS: Mineral Deposit Research Unit, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T ITA, Canada; 
Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T ITA, Canada; 
Franklin Geoscience Ltd., 24 Commanche Drive, Nepean, ON K2E 6E9, Canada; 
Altius Minerals Corporation, 66 Kenmount Road, St. John's, NL A1B 3V7, Canada
ABSTRACT: A ∼10-km-thick sequence of basaltic to rhyolitic volcanic rocks forms the arc component of the Cretaceous Lancones basin in northwestern Peru and underlies part of the Huancabamba deflection. The marine volcanic successions show markedly different compositional features and depositional facies consistent with a maturing arc within a shallowing marine basin. The earliest volcanism accompanying rifting was dominated by basaltic pillow lava and breccia with lesser aphyric to feldspar-quartz porphyritic felsic volcanic rocks. These volcanic successions filled the lowest exposed portion of the basin and were accompanied by volcanogenic massive sulfide (VMS) deposits, which are inferred to have formed in a localized but relatively deep marine setting. U-Pb zircon dating of felsic volcanic rocks associated with VMS deposits at Tambogrande indicates ages from 104.8 ± 1.3 to 100.2 ± 0.5 Ma for the ore-bearing volcanic sequence. The timing of onset of rift-related volcanism is not well constrained but is therefore of middle Albian age or older. Subsequent latest Albian to Turonian volcanism is composed of successions of relatively more felsic rich volcaniclastic rocks and yields U-Pb zircon ages of 99.3 ± 0.3 to 91.1 ± 1.0 Ma. These later volcanic successions are intercalated and overlain by siliciclastic and carbonate sedimentary sequences prevalent in the western forearc section of the Lancones basin. Finally, the basin was intruded by Late Cretaceous to Tertiary granitoids of the Coastal batholith. The genesis of the Cretaceous Lancones basin and other equivalent volcanic rift-related, marginal basins in western South America, including the western Peruvian trough, is related tectonically to the break-up of Gondwana. Early volcanism and associated VMS deposits formed in the Lancones basin during the Albian coincided with the initial rifting stage, prior to active oceanic spreading, between South America and Africa. During this time the relatively stationary western margin of continental South America was undergoing extension and rifting due to a westward and oceanward retreating arc, resembling a Mariana arc-type setting. The Mochica orogeny marks the termination of rifting, subsidence, and related volcanism along the western margin of South America. This orogenic event also broadly coincides with the onset of spreading of the South Atlantic and westward drift of the South American continent. Subsequent volcanism in the Lancones basin was more continental arclike under an Andean-type scenario. © 2010 by Economic Geology.
DOCUMENT TYPE: Article
SOURCE: Scopus

Stockar, R.a  b 
Facies, depositional environment, and palaeoecology of the Middle Triassic Cassina beds (Meride Limestone, Monte San Giorgio, Switzerland)
(2010) Swiss Journal of Geosciences, 103 (1), pp. 101-119. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954177609&partnerID=40&md5=666d43aa260fed1e86863c582fbf0126
AFFILIATIONS: Museo Cantonale di Storia Naturale, Viale Cattaneo 4, 6900 Lugano, Switzerland; 
Institut de Géologie et Paléontologie, Université de Lausanne, Anthropole, 1015 Lausanne, Switzerland
ABSTRACT: The Ladinian Cassina beds belong to the fossiliferous levels of the world-famous Middle Triassic Monte San Giorgio Lagerstätte (UNESCO World Heritage List, Canton Ticino, Southern Alps). Although they are a rich archive for the depositional environment of an important thanatocoenosis, previous excavations focused on vertebrates and particularly on marine reptiles. In 2006, the Museo Cantonale di Storia Naturale (Lugano) started a new research project focusing for the first time on microfacies, micropalaeontological, palaeoecological and taphonomic analyses. So far, the upper third of the sequence has been excavated on a surface of around 40 m2, and these new data complete those derived from new vertebrate finds (mainly fishes belonging to Saurichthys, Archaeosemionotus, Eosemionotus and Peltopleurus), allowing a better characterization of the basin. Background sedimentation on an anoxic to episodically suboxic seafloor resulted in a finely laminated succession of black shales and limestones, bearing a quasi-anaerobic biofacies, which is characterized by a monotypic benthic foraminiferal meiofauna and has been documented for the first time from the whole Monte San Giorgio sequence. Event deposition, testified by turbidites and volcaniclastic layers, is related to sediment input from basin margins and to distant volcanic eruptions, respectively. Fossil nekton points to an environment with only limited connection to the open sea. Terrestrial macroflora remains document the presence of emerged areas covered with vegetation and probably located relatively far away. Proliferation of benthic microbial mats is inferred on the basis of microfabrics, ecological considerations and taphonomic (both biostratinomic and diagenetic) features of the new vertebrate finds, whose excellent preservation is ascribed to sealing by biofilms. The occurrence of allochthonous elements allows an insight into the shallow-waters of the adjoining time-equivalent Salvatore platform. Finally, the available biostratigraphic data are critically reviewed. © 2010 Swiss Geological Society.
AUTHOR KEYWORDS: Cassina beds;  Depositional environment;  Facies;  Middle Triassic;  Monte San Giorgio;  Palaeoecology
DOCUMENT TYPE: Article
SOURCE: Scopus

Siemes, A., McCann, T., Fischer, A.
Palaeogene alluvial-volcaniclastic deposits in the Mesta Basin (SW Bulgaria): Depositional setting and basin evolution
(2010) Geological Magazine, 147 (3), pp. 321-338. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952553746&partnerID=40&md5=fbfa3fd85dec4ee09186706b2a312394
AFFILIATIONS: Steinmann Institut, Universitt Bonn, Nußallee 8, 53115 Bonn, Germany
ABSTRACT: The Mesta half-graben is one in a series of extensional basins in SW Bulgaria that record the onset of extension within the Rhodope Zone in the Late Eocene. Tectonic activity on a continuous detachment along the eastern margin was a major control on subsidence, accommodation space creation, sediment supply and facies distribution in the basin. The sedimentary architecture was complicated by synsedimentary rotation, the presence of intrabasinal faults and the resulting compartmentalization, as well as synsedimentary volcanic activity. Facies and structural analysis of a key transverse section in the central part of the basin, together with supporting observations from other parts of the basin, indicate a pulsed tectono-sedimentary evolution of the basin with three distinct stages. The first stage (Late Eocene) is a phase of rapid extension with an initial alluvial setting. Basin margin fans and an axial fluvial through-drainage system were the major depositional systems in this stage. The second stage (Early Oligocene) marks the onset of volcanic activity within the Mesta Basin and is characterized by the formation of volcanic centres, an intense phase of explosive volcanism and rapid infilling of the previous basin topography with volcanic material deposited from pyroclastic density currents. The third stage (Late Oligocene) represents waning volcanic activity in a mixed alluvial-volcaniclastic environment. This stage is characterized by alternating alluvial and volcaniclastic depositional cycles, as well as partial reworking of volcanic material. © Cambridge University Press 2009.
AUTHOR KEYWORDS: Aegean extension;  Alluvial;  Detachment fault;  Half-graben;  Southwest Bulgaria;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Sorbino, G., Sica, C., Cascini, L.
Susceptibility analysis of shallow landslides source areas using physically based models
(2010) Natural Hazards, 53 (2), pp. 313-332. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77951976387&partnerID=40&md5=02ac80affa9d55261a41cc66a0f0516f
AFFILIATIONS: Department of Civil Engineering, University of Salerno, Salerno, Italy
ABSTRACT: Rainfall-induced shallow landslides of the flow-type involve different soils, and they often cause huge social and economical disasters, posing threat to life and livelihood all over the world. Due to the frequent large extension of the rainfall events, these landslides can be triggered over large areas (up to tens of square kilometres), and their source areas can be analysed with the aid of distributed, physically based models. Despite the high potential, such models show some limitations related to the adopted simplifying assumptions, the quantity and quality of required data, as well as the use of a quantitative interpretation of the results. A relevant example is provided in this paper referring to catastrophic phenomena involving volcaniclastic soils that frequently occur in southern Italy. Particularly, three physically based models (SHALSTAB, TRIGRS and TRIGRS-unsaturated) are used for the analysis of the source areas of huge rainfall-induced shallow landslides occurred in May 1998 inside an area of about 60 km2. The application is based on an extensive data set of topographical, geomorphological and hydrogeological features of the affected area, as well as on both stratigraphical settings and mechanical properties of the involved soils. The results obtained from the three models are compared by introducing two indexes aimed at quantifying the "success" and the "error" provided by each model in simulating observed source areas. Advantages and limitations of the adopted models are then discussed for their use in forecasting the rainfall-induced source areas of shallow landslides over large areas. © Springer Science+Business Media B.V. 2009.
AUTHOR KEYWORDS: Landslide susceptibility mapping;  Shallow landslides;  Source area;  Triggering mechanism;  Volcaniclastic soils
DOCUMENT TYPE: Article
SOURCE: Scopus

Gangloff, R.A.a , Fiorillo, A.R.b 
Taphonomy and paleoecology of a bonebed from the prince creek formation, North Slope, Alaska
(2010) Palaios, 25 (5), pp. 299-317. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77951533728&partnerID=40&md5=a1880ee1a35d01762d2160edc443f7ef
AFFILIATIONS: Museum of Paleontology, University of California, 1101 Valley Life Sciences Building, Berkeley, CA 94720-4780, United States; 
Museum of Nature and Science, P.O. Box 151469, Dallas, TX 75315, United States
ABSTRACT: The late CampanianMaastrichtian Liscomb Bonebed is the richest source of dinosaur remains thus far documented in the polar regions. This bed is formally defined herein and assigned to the upper part of the Prince Creek Formation; the bonebed and several other organic-rich beds are part of a 178 m sequence of fluvial and volcaniclastic deposits. The Liscomb Bonebed is a mudstone rich in clay, comminuted plant remains, and palynomorphs with a total organic carbon (TOC) of 6.8010.55. It contains a multitaxic, low-diversity, dinosaur assemblage, dominated by Edmontosaurus sp., which is primarily represented by late juveniles. Four theropod taxa are almost exclusively represented by isolated teeth. With >6000 specimens collected, the assemblage is characterized by a Minimum Number of Individuals (MNI) of 36, dominance of Voorhies Groups I and II, and an underrepresentation of teeth, skulls, and girdles. Bones are highly fragmented and exhibit low weathering and abrasion indices. Bite marks occur on slightly more than 1 of elements. The densest accumulations of bone are typically found in the middle third of the bed with the largest bones at the bottom. The Liscomb Bonebed assemblage resulted from mass mortality associated with overbank floods that formed floodplain mires and ponds. Data from the current study clearly establish the Alaskan Arctic as the year-round residence of a rich dinosaur fauna and add further support to the hypotheses that even high-latitude hadrosaurids were gregarious and formed social groups. © 2010 SEPM (Society for Sedimentary Geology).
DOCUMENT TYPE: Article
SOURCE: Scopus

Chetel, L.M.a  b , Carroll, A.R.a 
Terminal infill of Eocene Lake Gosiute, Wyoming, U.S.A
(2010) Journal of Sedimentary Research, 80 (5-6), pp. 492-514. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953825018&partnerID=40&md5=896b85ea11c587df40b9df54e450eb2a
AFFILIATIONS: Department of Geoscience, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, United States; 
BP America, 200 Westlake Park Boulevard, Houston, TX 77079, United States
ABSTRACT: Deposition of lacustrine sediments in the greater Green River Basin was progressively terminated in the middle Eocene as volcaniclastic detritus prograded across the basin; the lacustrine sediment of the Laney Member was replaced by deposition of the deltaic and fluvial sediments of the volcaniclastic Bridger and Washakie formations and the Sand Butte Bed of the Laney Member. The transition from the deposition of lacustrine to alluvial sediment also records a reversal in the direction of drainage across the basin that occurred between 49.5 Ma and 48.9 Ma. Prior to this transition, drainage entered the basin from the east and the arkosic detritus of the Cathedral Bluffs Member of the Wasatch Formation was deposited in the Washakie and Great Divide subbasins. At the same time evaporitic sediments of the Wilkins Peak Member of the Green River Formation accumulated simultaneously in the Bridger Basin, indicating that the clastic sediment was baffled east of the Rock Springs Arch, an intrabasinal structural high. The subsequent transition to deposition of the Laney Member is traditionally interpreted as an isochronous expansion of Lake Gosiute across the greater Green River Basin. Alternatively, the transition may have been diachronous with continued accumulation of the Wilkins Peak Member in the Bridger Basin coinciding with the earliest deposition of the Laney Member in the Washakie Basin. By 48.9 Ma the dominant drainage was clearly from the west, which reflects the capture of an external drainage network through the northwest corner of the basin that delivered extrabasinal volcaniclastic detritus to the greater Green River Basin. More broadly, these results illustrate that the geomorphic evolution of the landscape influenced the character of sedimentary fill in the nonmarine greater Green River Basin. Copyright © 2010, SEPM (Society for Sedimentary Geology).
DOCUMENT TYPE: Article
SOURCE: Scopus

Melezhik, V.A.a  b , Fallick, A.E.c 
On the Lomagundi-Jatuli carbon isotopic event: The evidence from the Kalix Greenstone Belt, Sweden
(2010) Precambrian Research, 179 (1-4), pp. 165-190. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950595120&partnerID=40&md5=0118797cccefc6b11dca00ccc2ef6d35
AFFILIATIONS: Geological Survey of Norway, Leiv Eirikssons vey 39, N-4791 Trondheim, Norway; 
Centre for Geobiology, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway; 
Scottish Universities Environmental Research Centre, East Kilbride, Glasgow, G75 0QF Scotland, United Kingdom
ABSTRACT: We report a significant new database on the carbon and oxygen isotopic analyses (233 whole-rock, and 43 microcored samples) obtained from sedimentary dolostones in the Kalix Greenstone Belt from the Fennoscandian Shield of Sweden. This characterises the second half of the prominent Palaeoproterozoic Lomagundi-Jatuli positive carbon-isotope excursion. Within a 600 m-thick succession of alternating volcanic, volcaniclastic, siliciclastic and dolomitic rocks from greenschist-epidote-amphibolite metamorphic facies, the least altered dolostone samples show a gentle oscillation between +2‰ and +4‰ throughout stratigraphy with a second-order positive excursion from +4‰ through +8‰, and gradually back again to +4‰ in the c. 150 m-thick unit in the middle and upper parts of the succession. This second-order excursion is superimposed on the general relatively rapid δ13C decline at the second half of the Lomagundi-Jatuli isotopic event and coincides with the transition from a marine-influenced rift to a passive margin setting. If the excursion is global, it would reveal internal fine structure of the Lomagundi-Jatuli isotopic excursion; if not, basinal local factors are the main players. Lithostratigraphic and C-isotope correlation between Kalix and neighbouring Peräpohja Schist Belt successions, 40-km-apart, suggest an incomplete geological record in both successions despite the absence of obvious non-depositional unconformities. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Carbon isotopes;  Dolostone;  Fennoscandian Shield;  Palaeoproterozoic;  Passive margin;  Rift;  Rimmed shelf;  Stromatolites
DOCUMENT TYPE: Article
SOURCE: Scopus

Shalev, E.a  b , Kenedi, C.L.a  b , Malin, P.a  b , Voight, V.c , Miller, V.c , Hidayat, D.c , Sparks, R.S.J.d , Minshull, T.e , Paulatto, M.e , Brown, L.f , Mattioli, G.g 
Three-dimensional seismic velocity tomography of Montserrat from the SEA-CALIPSO offshore/onshore experiment
(2010) Geophysical Research Letters, 37 (9), art. no. L00E17, . Cited 8 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952115288&partnerID=40&md5=80a7a0b1007a5d99b0fe33826091d447
AFFILIATIONS: Department of Geosciences, Cornell University, 2146 Snee Hall, Ithaca, NY 14853, United States; 
Department of Geosciences, Pennsylvania State University, 540 Deike Bldg., University Park, PA 16802, United States; 
Institute of Earth Science and Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; 
Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701, United States; 
National Oceanography Centre, University of Southampton, European Way, Southampton SO14 3ZH, United Kingdom; 
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, United Kingdom; 
Department of Geosciences, University of Arkansas, Fayetteville, AK, United States
ABSTRACT: The SEA-CALIPSO experiment in December 2007 incorporated a sea-based airgun source, and seismic recorders both on Montserrat and on the adjacent sea floor. A high quality subset of the data was used for a first arrival P-wave velocity tomographic study. A total of more than 115,000 traveltime data from 4413 airgun shots, and 58 recording stations, were used in this highresolution tomographic inversion. The experiment geometry limited the depth of well resolved structures to about 5 km. The most striking features of the tomography are three relatively high velocity zones below each of the main volcanic centers on Montserrat, and three low velocity zones flanking Centre Hills. We suggest that the high velocity zones represent the solid andesitic cores of the volcano complexes, characterized by wave speeds faster than adjacent volcaniclastic material. The low velocity zones may reflect porous volcaniclastic material and/or alteration by formerly active hydrothermal systems. Copyright © 2010 by the American Geophysical Union.
DOCUMENT TYPE: Article
SOURCE: Scopus

Martens, U.a , Weber, B.b , Valencia, V.A.c 
U/Pb geochronology of devonian and older paleozoic beds in the southeastern maya block, central America: Its affinity with peri-gondwanan terranes
(2010) Bulletin of the Geological Society of America, 122 (5-6), pp. 815-829. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953746307&partnerID=40&md5=116ed8a714ed0b49ae33c88f8e7e4bde
AFFILIATIONS: Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, CA 94305, United States; 
División Ciencias de la Tierra, Centro de Investigación Científica y de Educación, Superior de Ensenada (CICESE), 22860 Ensenada, Baja California, Mexico; 
Department of Geosciences, University of Arizona, Tucson, AZ, United States
ABSTRACT: Paleozoic rocks of the Maya (Yucatan) block of Central America include granitoids, rhyolitic-dacitic volcanic rocks, clastic sedimentary strata ranging from conglomerate to shale/phyllite, and minor limestone. To date, published isotopic ages, paleontologic data, and interpretations of field relations have been contradictory. For instance, U/Pb ages of zircon and monazite from granitoids yield Silurian-Devonian ages (ca. 420-405 Ma); the granitoids are bordered by metasedimentary contact aureoles, yet the bulk of their protolith has been assigned to the Pennsylvanian-Permian (Macal Formation or Santa Rosa Group). In this paper, we resolve the paradox by showing that pre-Lower Devonian beds are present in the Maya Mountains and constitute the wall rock for the intrusions. We dated 23 igneous zircons from a rhyolite inter bedded with conglomerates obtaining a 406 +7/-6 Ma (2s) median U/Pb age, which represents the time of eruption of the previously recognized volcaniclastic Bladen Formation. Further-more, U/Pb geochronology of detrital zircon grains from a sandstone cobble, and outcrops of sandstone and quartzite yielded equivalent age spectra, indicating that they represent a separate geologic unit, which we herein define as the Baldy unit. Recognition of a distinct, pre-Devonian unit is justified because the sandstone cobble was collected from a conglomerate associated with the dated rhyolite, implying that the Baldy unit must have been deposited, lithified, exposed, and eroded before deposition of the Bladen Formation. The Baldy unit predates Silurian-Devonian magmatism because it does not contain interbedded volcanic rocks and is intruded by the dated granites. The five youngest detrital zircons of Baldy sedimentary rocks yielded ages in the 600-520 Ma range. These features imply that Baldy deposition took place some time between the Cambrian and Silurian. Baldy zircon age spectra have peaks at ca. 1.52 Ga, ca. 1.21 Ga, and ca. 1.02 Ga, consistent with provenance from Baltica or Amazonia, not Laurentia. Based on our new data and previously known geologic attributes of the Maya block, we propose that, during the Cambrian-Silurian, the block's position was along the West Amazonia side of Gondwana's periphery. © 2010 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Li, Z.-X.a , Li, X.-H.b , Wartho, J.-A.a  e , Clark, C.a , Li, W.-X.c , Zhang, C.-L.d , Bao, C.d 
Magmatic and metamorphic events during the early Paleozoic Wuyi-Yunkai orogeny, southeastern South China: New age constraints and pressure-temperature conditions
(2010) Bulletin of the Geological Society of America, 122 (5-6), pp. 772-793. Cited 10 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77949276042&partnerID=40&md5=6ffb0aa833c0e46f1778773bc3697c33
AFFILIATIONS: Institute for Geoscience Research, Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia; 
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100027, China; 
Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 
Nanjing Institute of Geology and Mineral Resources, Nanjing 210016, China; 
School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287, United States
ABSTRACT: The early Paleozoic Wuyi-Yunkai orogen in South China is a major orogenic belt in East Asia that formed at a similar time as the classic Caledonian orogeny in Europe. Despite the possibility of its being one of the few examples of intraplate orogenesis in the world, details about the orogen remain poorly defined. In this study, we provide age constraints on metamorphic and magmatic events in the eastern segment of the orogen, and the protoliths of the amphibolite-facies metamorphic rocks found there. By combining previous work with our new metamorphic and petrogenetic analyses, we present the following findings: (1) the Wuyi-Yunkai orogeny occurred between mid-Ordovician (>460 Ma) and earliest Devonian (ca. 415 Ma) time; (2) amphibolite-facies metamorphism in the eastern Wuyi-Yunkai orogen occurred between ca. 460 and 445 Ma, whereas cooling below 500-300 °C occurred by ca. 420 Ma; (3) the orogen exhibits a clockwise pressure-temperature (P-T) path and a maximum pressure of >8 kbar, indicating crustal thickening during the orogeny; (4) protoliths of the high-grade metamorphic rocks in the eastern segment of the orogen were dominantly Neoproterozoic (840-720 Ma) volcanic and volcaniclastic rift successions and younger deposits formed in a failed rift, and Paleoprotero zoic rocks account for only a small proportion of the outcrops; and (5) the analyzed granites indicate a mixed source of Paleoprotero zoic basement and Neoproterozoic conti nental rift rocks, with elevated melt temperatures of >800 °C, which are interpreted as reflecting dehydration melting of basin sediments taken to below midcrustal levels. © 2010 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Lenhardt, N.a  e , Böhnel, H.b , Wemmer, K.c , Torres-Alvarado, I.S.d , Hornung, J.a , Hinderer, M.a 
Petrology, magnetostratigraphy and geochronology of the Miocene volcaniclastic Tepoztlán Formation: Implications for the initiation of the Transmexican Volcanic Belt (Central Mexico)
(2010) Bulletin of Volcanology, 72 (7), pp. 817-832. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956175080&partnerID=40&md5=4bf0c8410edfb17c9ebcaf13ec005414
AFFILIATIONS: Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Darmstadt, Germany; 
Centro de Geociencias, Universidad Nacional Autónoma de México, Querétaro, Mexico; 
Geowissenschaftliches Zentrum Göttingen, Göttingen, Germany; 
Departamento de Sistemas Energéticos, Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Temixco, Mexico; 
Department of Geology, University of Pretoria, Pretoria 0002, South Africa
ABSTRACT: The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time intervall 22.8-18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant mode of deposition: (1) the fluvial dominated Malinalco Member (22.8-22.2 Ma), (2) the volcanic dominated San Andrés Member (22.2-21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3-18.8 Ma). © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Central Mexico;  K-Ar Geochronology;  Magnetostratigraphy;  Miocene;  Tepoztlán Formation;  Transmexican Volcanic Belt;  Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Doronzo, D.M., Dellino, P.
A fluid dynamic model of volcaniclastic turbidity currents based on the similarity with the lower part of dilute pyroclastic density currents: Evaluation of the ash dispersal from ash turbidites
(2010) Journal of Volcanology and Geothermal Research, 191 (3-4), pp. 193-204. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950518103&partnerID=40&md5=d5a957af83dfbffad199234d9a3a9d77
AFFILIATIONS: Centro Interdipartimentale di Ricerca sul Rischio Sismico e Vulcanico (CIRISIVU), C/O Dipartimento Geomineralogico, Università di Bari, Via E. Orabona 4, 70125 Bari, Italy
ABSTRACT: Subaqueous sediment density currents have variable flow structures, depending on particle size and volumetric concentration. They form both in ocean basins and in volcanic districts, where subaqueous density currents are generated by collapse of slope and primary pyroclastic material entering the sea, respectively. A particular type of such flows is represented by volcaniclastic turbidity currents, which form by the subaqueous remobilization of primary pyroclastic deposits. In this work, a fluid dynamic model of volcaniclastic turbidity currents is presented and applied to the currents that generated the Craco (Southern Italy) volcaniclastic deposits. The deposits consist of thick laminated to massive beds, which formed from the remobilization of thin fine-ash pyroclastic fall deposits, in an area far away from the original volcanic source. Our model is based on the sedimentological features of the deposits and particle physical characteristics. It allows the calculation of velocity, thickness and Reynolds number of the currents. Furthermore, a relationship between the current thickness, laminae thickness and paleo-slope angle is obtained, which allows to evaluate the thickness of the primary pyroclastic fallout deposits. Our model can be useful for obtaining an estimation of the primary distal ash dispersal by the characteristics of the associated subaqueous volcaniclastic deposits. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Fine-ash dispersal;  Fluid dynamics of dilute currents;  Volcaniclastic turbidity currents
DOCUMENT TYPE: Article
SOURCE: Scopus

Hocking, M.W.A.a , Hannington, M.D.a , Percival, J.B.b , Stoffers, P.c , Schwarz-Schampera, U.d , de Ronde, C.E.J.e 
Clay alteration of volcaniclastic material in a submarine geothermal system, Bay of Plenty, New Zealand
(2010) Journal of Volcanology and Geothermal Research, 191 (3-4), pp. 180-192. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950520649&partnerID=40&md5=02e25d874a43a6f58e7c866214cc5471
AFFILIATIONS: Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, University of Ottawa, Marion Hall, 140 Louis Pasteur, Ottawa, Ontario, K1N 6N5, Canada; 
Geological Survey of Canada, Natural Resources Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada; 
Institute of Geosciences, University of Kiel, Olshausenstr. 40, 24118 Kiel, Germany; 
Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany; 
Institute of Geological and Nuclear Sciences, P.O. Box 31-312, Lower Hutt, New Zealand
ABSTRACT: The Calypso Hydrothermal Vent Field (CHVF) is located along an offshore extension of the Taupo Volcanic Zone (TVZ), an area of abundant volcanism and geothermal activity on the North Island of New Zealand. The field occurs within a northeast-trending submarine depression on the continental shelf approximately 10-15 km southwest of the White Island volcano in the Bay of Plenty. The graben has been partially filled by tephra from regional subaerial volcanic eruptions, and active hydrothermal venting occurs at several locations along its length. The vents occur at water depths of 160 to 190 m and have temperatures up to 201 °C. Recovered samples from the vent field include variably cemented and veined volcaniclastic sediments containing an assemblage of clay minerals, amorphous silica, barite, As-Sb-Hg sulfides, and abundant native sulfur. The volcanic glass has been altered primarily to montmorillonite and mixed-layer illite-montmorillonite; illite, and possibly minor talc and mixed-layer chlorite-smectite or chlorite-vermiculite are also present. A hydrothermal versus diagenetic origin for the smectite is indicated by the presence of both illite and mixed-layer clays and by the correlation between the abundance of clay minerals and the abundance of native sulfur in the samples. The mineralization and alteration of the volcanic host rocks are similar to that observed in near-neutral pH geothermal systems on land in the TVZ (e.g., Broadlands-Ohaaki). However, the clay minerals in the CHVF have a higher concentration of Mg in the dioctahedral layer and a higher interlayer Na content than clay minerals from Broadlands-Ohaaki, reflecting the higher concentrations of Mg and Na in seawater compared to meteoric water. Minerals formed at very low pH (e.g., kaolinite and alunite), typical of steam-heated acid-sulfate type alteration in the TVZ geothermal environment, were not found. Mixing with seawater likely prevented the formation of such low-pH mineral assemblages. The occurrence of illite and mixed-layer illite-smectite close to the seafloor in the CHVF, rather than at depth as in the Broadlands system, is interpreted to reflect the higher pressures associated with submarine venting. This allows hotter fluids to be discharged before they boil, and thus minerals that are encountered mainly at depth in subaerial geothermal systems can form close to the seafloor. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Clay alteration;  Submarine geothermal systems;  Taupo Volcanic Zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Violante, R.a  e , Osella, A.b , Vega, M.D.L.b , Rovere, E.c  e e  , Osterrieth, M.d 
Paleoenvironmental reconstruction in the western lacustrine plain of Llancanelo Lake, Mendoza, Argentina
(2010) Journal of South American Earth Sciences, 29 (3), pp. 650-664. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77951769119&partnerID=40&md5=f04501315cfb89cccc1785310d0930da
AFFILIATIONS: Servicio de Hidrografía Naval, División Geología y Geofísica, Buenos Aires, Argentina; 
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires/CONICET, Departamento de Física, Argentina; 
Servicio Geológico Minero Argentino, Dirección Geología Regional, Buenos Aires, Argentina; 
Universidad Nacional de Mar del Plata, Centro de Geología de Costas y del Cuaternario, Mar del Plata, Argentina; 
GevasRed (Grupo de Estudio de Volcanes, Ambiente y Salud), Argentina
ABSTRACT: Lakes are key sites for studying paleoclimates. Llancanelo Lake (southern Mendoza Province, western Argentina) is an endoreic, highly saline water body located in the southern extreme of a tectonic basin, the Central or Huarpes Depression. The lake is located between the Andean Cordillera, San Rafael Block and Payenia Volcanic Field. The lake evolved as a major regional depocenter during the Pliocene-Quaternary, hence it contains important thicknesses of intra and extra basinal clastic and evaporitic sediments mainly dominated by volcaniclastic products. The main conditioning factors in the lake evolution were arc and back-arc volcanism as well as climatic changes. Geomorphological and sedimentary evidence supports the hypothesis that the lake was in past times larger than in present days. This paper estimates the lake's former extension on the western lacustrine plain using electromagnetic induction (EMI) and geoelectricity (Multielectrode Resistivity Meter) surveys, as well as shallow wells, along an 8. km long transect perpendicular to the lake's western shoreline. The geophysical and sedimentological information, as well as microfaunal studies, lab analysis and petrographic/EDAX determinations, support the presence, in the subsoil, of a lacustrine sequence at least 30. m thick composed mainly of volcaniclastic sediments. Volcanic eruptions and climatic changes influenced the evolution of the lake, producing intercalations in the lacustrine sedimentary sequences of ash layers, evaporites, soils, and eolian and swamp deposits. © 2009 Elsevier Ltd.
AUTHOR KEYWORDS: Electromagnetic induction methods;  Geoelectrical soundings;  Llancanelo Lake;  Paleoenvironmental reconstruction;  Volcaniclastic sediments
DOCUMENT TYPE: Article
SOURCE: Scopus

Belousov, A.a  b , Belousova, M.a  b  c , Chen, C.-H.a , Zellmer, G.F.a  d 
Deposits, character and timing of recent eruptions and gravitational collapses in Tatun Volcanic Group, Northern Taiwan: Hazard-related issues
(2010) Journal of Volcanology and Geothermal Research, 191 (3-4), pp. 205-221. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950520935&partnerID=40&md5=689113f566fb7d2531d10a970bd34916
AFFILIATIONS: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang, Taipei 11529, Taiwan; 
Earth Observatory of Singapore, Nanyang Technological University, N2-01a-15, 50 Nanyang Avenue, 639798 Singapore, Singapore; 
Institute of Volcanology and Seismology, Petropavlovsk, Russian Federation; 
Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY10964, United States
ABSTRACT: Taipei City, with a population of around 8 million, as well as two nuclear power plants is located in close proximity to the Quaternary, dominantly andesitic Tatun Volcanic Group (TVG) of Northern Taiwan. We have investigated the stratigraphy of the youngest volcaniclastic deposits, as well as the morphology of lava flows and domes of the TVG in order to reconstruct the character and timing of the most recent eruptions and related hazardous events in the area.Our data indicate that recent eruptions of the group were dominated by long-term, voluminous extrusions of crystal-rich, very viscous lavas. These eruptions formed closely spaced monogenetic domes and lava flows. Based on morphological parameters of the lava flows (thicknesses 80-150m, lengths up to 5.6km, and volumes up to 0.6km3), average rates of magma effusion ranged from 1 to 10m3/s, eruption durations from 500 to 1800days, and lava front speeds from 0.5 to 6m/h.Explosive activity of TVG was diverse, ranging from weak phreatic to highly explosive (VEI 4) Plinian eruptions; vulcanian activity with deposition of lithic ashes was most common. Interaction of rising magma with ground water frequently occurred during the eruptions.This study presents the first radiocarbon dates of various volcaniclastic deposits of the TVG, which indicate that Cising, Siaoguanyin, and possibly Huangzuei volcanoes had magmatic eruptions in the period 13,000-23,000years ago. In addition, Mt. Cising had a phreatic eruption 6000years ago, and possibly an effusive eruption just before that. Gravitational collapses of volcanic edifices with volumes 0.01-0.1km3 and H/L 0.16-0.25 were also common. They occurred on intersections with tectonic faults and may have been triggered by seismic activity. The youngest collapses occurred at Mt. Siaoguanyin (23,000 BP) and Mt. Cising (6000 BP).It is concluded that the TVG should be considered volcanically active. The results of this study provide a basis for volcanic hazard assessment and mitigation in the area. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Edifice collapse;  Explosive eruption;  Extrusive eruption;  Pyroclastic;  Taiwan;  Volcanic hazard
DOCUMENT TYPE: Article
SOURCE: Scopus

Aharipour, R.a  b , Moussavi, M.R.b , Mosaddegh, H.a , Mistiaen, B.c 
Facies features and paleoenvironmental reconstruction of the Early to Middle Devonian syn-rift volcano-sedimentary succession (Padeha Formation) in the Eastern-Alborz Mountains, NE Iran
(2010) Facies, 56 (2), pp. 279-294. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952670851&partnerID=40&md5=acaf3f3604b72fb721aaea6f2e03e84b
AFFILIATIONS: School of Earth Sciences, Damghan University of Basic Sciences, PO Box 36715-364 begin_of_the_skype_highlighting              36715-364      end_of_the_skype_highlighting, Damghan, Iran; 
Department of Geology, Faculty of Earth Sciences, University of Shahid Beheshti, Tehran, Iran; 
Laboratoire de Paleontologie Stratigraphique, FLST and ISA, Geosystemes UMR 8157 CNRS, 48 Bd Vauban, 59046 Lille cedex, France
ABSTRACT: The Padeha Formation in the Eastern-Alborz Mountains (northeast Iran) is an Early to Middle Devonian syn-rift succession. Siliciclastic rocks (conglomerates, sandstones, mudstones, and red paleosols) to non-marine carbonates (yellowish calcretes, dolocretes, stromatolites, and sandy bivalve packstone) associated with volcaniclastic rocks (basalts or andesites and tuffs) are present in this succession. Facies analysis led to the recognition of three facies associations that are deposited in three terrestrial environments (alluvial fan, distal fan, and palustrine/lacustrine). Its sedimentary fill pattern and association with mafic volcaniclastic rocks indicate that this formation is related to the initial phase of a rift basin (intracratonic rift). Paleosols of this formation are good indicators for recognition of paleoenvironmental factors (climatic changes from semi-arid to sub-humid with annual fluctuation, small and short gross-like vegetation cover, subaerial exposure, very shallow lake, volcanic source rocks, and early meteoric diagenesis). © Springer-Verlag 2009.
AUTHOR KEYWORDS: Devonian;  Eastern-Alborz Mountains;  Intracratonic rift basin;  Padeha Formation;  Paleosol;  Terrestrial environment
DOCUMENT TYPE: Article
SOURCE: Scopus

Bessonova, E.P.a , Sharapov, V.N.a , Chudnenko, K.V.b , Cherepanova, V.K.a 
A new model of thermal and physicochemical dynamics for volcanogenic epithermal deposits (Asacha Deposit, Kamchatka)
(2010) Doklady Earth Sciences, 431 (2), pp. 453-457. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952233885&partnerID=40&md5=bae5a10a9fc1770ed7460a07fbc6b40f
AFFILIATIONS: Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk 630090, Russian Federation; 
Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, ul. Favorskogo 1A, Irkutsk 650033, Russian Federation
DOCUMENT TYPE: Article
SOURCE: Scopus

Harlan, S.S.a , Morgan, L.A.b 
Paleomagnetic results from Tertiary volcanic strata and intrusions, Absaroka Volcanic Supergroup, Yellowstone National Park and vicinity: Contributions to the North American apparent polar wander path
(2010) Tectonophysics, 485 (1-4), pp. 245-259. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950537967&partnerID=40&md5=2561606f5934745b673d3694c3ac97bd
AFFILIATIONS: Department of Atmospheric, Oceanic and Earth Sciences, George Mason University, Fairfax, VA 22030, United States; 
U.S. Geological Survey, PO Box 25046, MS 966, Denver, CO 80225, United States
ABSTRACT: We report paleomagnetic and rock magnetic data from volcanic, volcaniclastic, and intrusive rocks of the 55-44Ma Absaroka Volcanic Supergroup (AVS) exposed along the northeastern margin of Yellowstone National Park and adjacent areas. Demagnetization behavior and rock magnetic experiments indicate that the remanence in most samples is carried by low-Ti titanomagnetite, although high-coercivity phases are present in oxidized basalt flows. Paleomagnetic demagnetization and rock magnetic characteristics, the presence of normal and reverse polarity sites, consistency with previous results, and positive conglomerate tests suggest that the observed remanences are primary thermoremanent magnetizations of Eocene age (c. 50Ma). An in situ grand-mean for 22 individual site- or cooling-unit means from this study that yield acceptable data combined with published data from Independence volcano yields a declination of 347.6° and inclination of 59.2° (k=21.8, α95=6.8°) and a positive reversal test. Averaging 21 virtual geomagnetic poles (VGPs) that are well-grouped yields a mean at 137.1°E, 82.5°N (K=17.6, A95=7.8°), similar to results previously obtained from published studies from the AVS. Combining the VGPs from our study with published data yields a combined AVS pole at 146.3°E, 83.1°N (K=13.5, A95=6.2°, N=42 VGPs). Both poles are indistinguishable from c. 50Ma cratonic and synthetic reference poles for North America, and demonstrate the relative stability of this part of the Cordillera with respect to the craton. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Apparent polar wander;  Cenozoic volcanism;  Magnetic anomalies;  Paleomagnetism;  Rock magnetism;  Yellowstone National Park
DOCUMENT TYPE: Article
SOURCE: Scopus

Shane, P., Strachan, L.J., Smith, I.
Redefining the Waitemata Basin, New Zealand: A new tectonic, magmatic, and basin evolution model at a subduction terminus in the SW Pacific
(2010) Geochemistry, Geophysics, Geosystems, 11 (4), art. no. Q04008, . Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78149392562&partnerID=40&md5=92dd5a02eeb2eeb8819988fe90cc49be
AFFILIATIONS: SGGES, University of Auckland, Private Bag 92019, Auckland, New Zealand
ABSTRACT: The early Miocene Waitemata Basin has long been described as an interarc/intra-arc basin, formed between twin chains of arc volcanoes in Northland, New Zealand. However, deep marine, polymict, volcaniclastic conglomerates within the basin reveal tectonic and magmatic signals that are not evident from neighboring volcanic edifices. The conglomerates were deposited by high-density turbidity currents and debris flows and include single sediment cycle megaclasts of lava. These basaltic lavas have ocean island basalt (OIB)-like geochemical affinities and are precisely dated at 20 Ma by 40Ar-39Ar methods. Their age and the occurrence of subordinate clasts derived from an ophiolitic nappe to the north indicate the basin postdates the initiation of collision in the wider region. Contemporaneous calc-alkaline volcanism did occur some 250 km NW of the basin. However, the conglomerates lack clasts of calc-alkaline/arc affinities indicating an absence of arc-like volcanism in the vicinity of the basin. Recent tectonic models for the SW Pacific region and mantle tomography highlight the importance of wholesale slab detachment in driving early Miocene calc-alkaline volcanism and basin development. Although such models provide a slab window for the eruption of nonarc OIB-like magmas, they would not explain their localized occurrence at the proposed leading edge of the tear (Waitemata Basin), rather than progressively along the entire length of the detachment (Northland), as seen in other detachment settings. In addition, OIB-like volcanism predates the adjacent calc-alkaline volcanism on the margin of the basin, a transition that is the opposite of that found at other slab detachment settings. The occurrence of OIB-like volcanism is better explained by a lateral slab termination in the vicinity of the Waitemata Basin that allowed asthenospheric-derived magmas to erupt. The basin is inferred to have developed in response to asthenospheric upwelling and associated lithospheric extension or deformation associated with a slab termination zone. This study highlights the importance and potential of combined geochemical, geochronological, and sedimentological studies of conglomerates in reconstructing the geodynamic setting of a basin. Copyright 2010 by the American Geophysical Union.
AUTHOR KEYWORDS: Basalt;  Conglomerate;  Geochemistry;  Geochronology;  Subduction;  Waitemata basin
DOCUMENT TYPE: Article
SOURCE: Scopus

Becker, N.C.a , Fryer, P.b , Moore, G.F.b 
Malaguana-Gadao Ridge: Identification and implications of a magma chamber reflector in the southern Mariana Trough
(2010) Geochemistry, Geophysics, Geosystems, 11 (4), art. no. Q04X13, . 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78149385351&partnerID=40&md5=0ccfea2ecbe36149f8d8bda278b60c03
AFFILIATIONS: Pacific Tsunami Warning Center, Ewa Beach, HI 96706, United States; 
SOEST, University of Hawai'i, Manoa Honolulu, HI 96822, United States
ABSTRACT: Six-channel seismic reflection data reveal a magma chamber reflector beneath the Malaguana-Gadao Ridge, the southernmost segment of the spreading center in the Mariana Trough. For most of its length the spreading center in this active back-arc basin is morphologically similar to slow spreading mid-ocean ridges, having a deep central graben flanked by a zone of abyssal hill fabric. This southernmost segment, however, has a broad, smooth cross section, lacks a deep central graben, and is thus similar in morphology to fast spreading ridges (e.g., the East Pacific Rise). We identify a magma chamber at 1.5 s two-way travel time below the crest of the ridge. Observations from remotely operated vehicles along the ridge reveal not only fresh pillows, lobate, and sheet lava flows but also an abundance of volcaniclastic debris and intense hydrothermal activity. These observations, together with the "fast spreading" morphology of the ridge, suggest that this segment has a considerably higher magma supply than is typical in the Mariana Trough. We suggest that the volcanic arc or enhanced melting of a hydrated mantle is supplying volatile-rich magma as evidenced by a highly negative coefficient of reflection, -0.42, for this MCR and the presence of evolved, highly vesicular lava and volcaniclastic materials. The southeastern Mariana back-arc basin spreading ridge does not compare readily with mechanical models for global mid-ocean ridge data sets because of marked asymmetry in both volcanism and deformation that may be the consequence of slab-related geometry in this part of the convergent margin system. Copyright 2010 by the American Geophysical Union.
AUTHOR KEYWORDS: Magma chamber;  Mariana;  Seismic reflection;  Spreading center
DOCUMENT TYPE: Article
SOURCE: Scopus

Juliani, C., Fernandes, C.M.D.
Well-preserved Late Paleoproterozoic volcanic centers in the São Félix do Xingu region, Amazonian Craton, Brazil
(2010) Journal of Volcanology and Geothermal Research, 191 (3-4), pp. 167-179. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950516594&partnerID=40&md5=e2de51f846b63bb554be4e92192705bd
AFFILIATIONS: Instituto de Geociências, Universidade de São Paulo, Brazil
ABSTRACT: The Amazonian craton in the São Félix do Xingu city, southeast region of the Pará state, north of Brazil, hosts exceptionally well-preserved Paleoproterozoic bimodal magmatic units grouped in the Sobreiro and Santa Rosa formations. These formations are correlated to the Uatumã magmatic event, which is largely distributed in the Amazonian craton occupying more than 1,500,000km2. Geological mapping and petrographical observations reveal distinct spectra of volcanic facies in both formations. The basal calc-alkaline Sobreiro Formation is composed mainly of andesitic and dacitic lava flows and associated volcaniclastic facies of autoclastic origin, with subordinate pyroclastic flow deposits. This formation shows inferred eruption style that is similar to those in Flood Basalt Provinces, with rare scutulum-type lava shields. The upper A-type Santa Rosa Formation was generated by multicyclic explosive and effusive episodes predominantly associated with large fissures and is materialized by voluminous ignimbrites with subordinated ash-fall tuff, crystal tuff, lapilli-tuff, co-ignimbritic breccias, rhyolitic dikes and domes, and associated granitic porphyries and equigranular granitic intrusions. Ignimbrite and rhyolite dikes reveal conspicuous vertical flow pattern pointing to a fissure-controlled eruption, similar to Sierra Madre Occidental ignimbrite province. The proposed evolutionary model for the São Félix do Xingu units differs from those of other occurrences related to the Uatumã magmatic event in the Amazonian craton, characterized by predominance of A-type volcanism and contemporaneous granites. © 2010 Elsevier B.V.
AUTHOR KEYWORDS: Fissure-controlled;  Paleoproterozoic;  Stratigraphy;  Uatumã;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Cheng, R.a , Shen, Y.a , Yan, J.b , Li, Q.b , Li, X.b , Wang, Y.b , Li, F.a , Xu, Z.a 
Diagenesis of volcaniclastic rocks in Hailaer Basin
(2010) Acta Petrologica Sinica, 26 (1), pp. 47-54. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77949815773&partnerID=40&md5=58d845c98d341e5602ba8c1c1fc5a50a
AFFILIATIONS: College of Earth Sciences, Jilin University, Changchun 130061, China; 
Digital Interpretation Center of No. 1 Daqing Well-lgging Company, Daqin 163000, China
ABSTRACT: The microscopic study and analysis of the Cretaceous volcaniclastic samples from 40 drilling wells in Hailaer Basin show that, the speciality of the diagenesis is presented in welding, devitrification and recrystallization, formation and transform of clay minerals and replacement etc. There are three types of welding textures identified as weldings of magma or lava, magma fragment and hot ash. Devitrification and recrystallization were combined, showing special textures, such as a complex cementation of quartzs and siliceous matter resulted from the devitrification of rhyolitic glass and recrystallization. The forming and transforming of clay minerals started early at the initial stage of diagenesis, such as occuring of smectite. Lomonite and chlorite, some diagnostic minerals, would be products of special diagenesis rather than signs of beginning of metamorphism. The replacement-cementation and dissolution developed well in the volcaniclastic rocks during diagenesis, giving some great changes to the original types of rocks. The characteristics of diagenesis reveals the evolution of components and textures of the volcaniclastics in Hailaer Basin, which is useful to the lithological interpretation of loggings and prediction of porosity.
AUTHOR KEYWORDS: Diagenesis;  Hailaer Basin;  Speciality;  Volcaniclastic rock
DOCUMENT TYPE: Article
SOURCE: Scopus

Stiegler, M.T.a , Lowe, D.R.a , Byerly, G.R.b 
The petrogenesis of volcaniclastic komatiites in the Barberton Greenstone belt, South Africa: A textural and geochemical study
(2010) Journal of Petrology, 51 (4), art. no. egq008, pp. 947-972. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952707635&partnerID=40&md5=bb2db30ccf04e448f0e65f09d850b5b0
AFFILIATIONS: Department of Geological and Environment Sciences, Stanford University, Stanford, CA 94305, United States; 
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, United States
ABSTRACT: The Onverwacht Group of the 3·5-3·2 Ga Barberton greenstone belt, South Africa contains multiple stratigraphic units that include laterally extensive beds of komatiitic ash, accretionary lapilli, and lapilli. These units have been affected by pervasive silicification, serpentinization, or, less commonly, carbonate metasomatism. Silicification resulted in SiO2+K2O&lt;85 wt % and depletion of most other major and trace elements.Most of these tuffs have prominent high Hf/Hf* and Zr/Zr* (0.5-12), which cannot result from normal magmatic processes but are due to the typically immobile rare earth elements migrating during post-silicification fluid-rock interaction. Similarly, their low Ce/Ce* values do not reflect Archean surface redox conditions but the circulation of later oxidizing fluids. Despite this intense alteration, ratios of Al2O3 and TiO2 remain uniform and coherent within single volcanic units. These ratios indicate that most silicified tuffs are not petrogenetically related to the underlying or overlying komatiitic flow rocks and that each originated from either separate mantle sources or different partial melting conditions. Serpentinized tuffs retain komatiitic element abundances but Al2O3 fails to define a tight linear array with the demonstrably immobile elementsTi and Zr. We speculate that this is due to post-depositional mixing of Al-depleted and Al-undepleted tuff layers by aqueous currents. Excellent textural preservation of the silicified tuffs shows they are characterized by a dearth of phenocrysts, low particle vesicularity and abundance of fine vitric ash, suggesting the eruption and rapid quenching of superheated or near-liquidus anhydrous magmas. Minor assimilation of hydrated basaltic or ultramafic crust within the dry magma may have enhanced the surface phreatomagmatic explosivity while still allowing the magma to rise close to an adiabatic ascent path. However, textural and geochemical evidence for such a process is scarce. Temporal and compositional constraints show that the diversity in the types of komatiites throughout the Onverwacht Group can be accounted for by variations in plume-mantle dynamics and that komatiitic tuffs were deposited during intervals of volcanism characterized by low effusive eruptive volumes and/or low emplacement rates. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org.
AUTHOR KEYWORDS: Archean;  Greenstone belts;  Komatiite;  Petrogenesis;  Tuff
DOCUMENT TYPE: Article
SOURCE: Scopus

Guo, L.a  b , Liu, Y.a , Wang, Z.a , Song, D.a , Xu, F.c , Su, L.d 
The zircon U-Pb LA-ICP-MS geochronology of volcanic rocks in Baogutu areas, western Junggar
(2010) Acta Petrologica Sinica, 26 (2), pp. 471-477. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77949834452&partnerID=40&md5=292537f946df00ebaaeca36030be0a02
AFFILIATIONS: Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China; 
Key Laboratory of Western China' S Environmental Systems, Ministry of Education, Lanzhou 730000, China; 
Institute of Geology, Xinjiang Nonferrous Geoexploration Bureau, Urumqi 830000, China; 
Geological Lab. Center, China University of Geosciences, Beijing 100083, China
ABSTRACT: There is a great thickness of bathyal- and slope-facies volcanic-volcaniclastic sedimentary sequence at Baogutu area in southeast of western Junggar, which are named as Tailegula Formation, Baogutu Formation and Xibeikulas Formation, respectively. There have been controversies about the geological ages and stratigraphic subdivision about these strata for a long time. So we surveyed the stratum section at Baogutu area and separated zircons from basalt of the Tailegula Formation and tuff of Baogutu Formation and Xibeikulas Formation. LA-ICP-MS U-Pb dating on these zircon grains gives the 206Pb/238 U weighted mean ages of 357. 5 ± 5. 4Ma, 332. 1 ± 3. 0Ma and 336.3 ± 2. 5Ma, respectively, indicating that the strata sequence from bottom to top should be Tailegula Formation, Baogutu Formation and Xibeikulas Formation in turn, which were formed from Tournaisian to Visean of Early Carboniferous.
AUTHOR KEYWORDS: Baogutu;  U-Pb dating;  Volcanics;  West Junggar;  Zircon
DOCUMENT TYPE: Article
SOURCE: Scopus

Breesch, L.a , Swennen, R.a , Vincent, B.b , Ellison, R.c , Dewever, B.a 
Dolomite cementation and recrystallisation of sedimentary breccias along the Musandam Platform margin (United Arab Emirates)
Journal of Geochemical Exploration, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77949450190&partnerID=40&md5=31f27e020948da35d39c60b7cccf9dbd
AFFILIATIONS: Geologie, K.U.Leuven, Celestijnenlaan 200E, B-3001 Heverlee, Belgium; 
IFP, Géologie-Géochimie, 1-4 Avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France; 
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
ABSTRACT: Two main events of dolomite formation were identified along the southern border of the Late Jurassic Musandam carbonate platform of the UAE. The first dolomitisation phase (type 1) was restricted to specific stratigraphic layers in Jurassic platform limestones that were subsequently brecciated by mass flow and collapse processes on the platform margin. These dolomites are planar-s, have crystal sizes ranging from 5 to 25 μm and exhibit an orange to pink and sometimes zoned red-yellow luminescence. This dolomite phase was formed shortly after deposition by fluids of marine or slightly modified marine composition. The second dolomite phase (type 2) mainly affected dolomite type 1 breccias by recrystallisation, dolomite cementation and replacement. Type 2 dolomites are planar-e and non-planar-c, with crystal sizes between 20 and 70 μm. They have more elongated forms with purple luminescent to non-luminescent cores overgrown by pink to yellow luminescent rims. Stable isotope analyses show a covariant trend between δ18O and δ13C from marine (- 4.2 to - 1.8 and + 0.8 to + 2.1‰ VPDB respectively) towards depleted values (- 10.2 and - 8.9‰ VPDB respectively) . This depletion is explained by recrystallisation during type 2 dolomitisation and it is interpreted in terms of high temperatures during precipitation and the incorporation of light carbon as hydrocarbons matured. Dolomite type 2 formation is thought to be the result of tectonically induced fluid flow which supplied hot magnesium-rich fluids. Two possible time scenarios for this fluid flow event are proposed: 1) during thrust emplacement of the tectonic nappes on top of the Musandam Platform in the Late Cretaceous. Volcaniclastic and basaltic rocks of the Hawasina Complex and the Oman-UAE ophiolites are a possible magmatic source for magnesium in this case; or 2) coinciding with the migration of hot, post-evaporative brines along the Hagab thrust, which acted as a fluid conduit during the Cenozoic orogeny. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Cementation;  Dolomite;  Fluid flow;  Musandam;  Oxygen isotopes;  Recrystallisation
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Casalbore, D.a , Romagnoli, C.b , Chiocci, F.a  c , Frezza, V.c 
Morpho-sedimentary characteristics of the volcaniclastic apron around Stromboli volcano (Italy)
(2010) Marine Geology, 269 (3-4), pp. 132-148. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75849133167&partnerID=40&md5=709cfa066561214b808e47df5e0e1952
AFFILIATIONS: CNR, Istituto di Geologia Applicata e Geoingegneria, Roma, P.le Aldo Moro 5, Roma, 00185, Italy; 
University of Bologna, Dip. Scienze della Terra e Geologico-Ambientali, P.zza di Porta S.Donato 1, 40126 Bologna, Italy; 
University of Roma La Sapienza, Dip. Scienze della Terra, P.le Aldo Moro 5, Roma, 00185, Italy
ABSTRACT: Submarine portions of Stromboli volcano account for about 98% of the whole extent of the volcanic edifice and are mostly covered by volcaniclastic sediments that made up a modern volcaniclastic apron. The architecture and main sedimentary processes acting within the apron are depicted through the integration of geophysical evidence (multibeam, long-range side scan sonar and seismic data) and seafloor sampling. The apron shows, on the whole, a large variability both across and along slope of morphologies and deposits related to mass-wasting and reworking processes, passing into areas covered by hemipelagic sedimentation. A large spectrum of erosive-depositional features was recognized on the surface of the apron. On shallower areas (i.e. submerged shelves, shore platforms and depositional terraces), submarine features related to wave action and sea-level fluctuations are present; they mainly act as temporary storing and reworking areas for volcaniclastic material derived from subaerial portions. Unconfined cohesionless inertial flows commonly dominate the upper slope, where gradients are very high (up to 35°) and grain-to-grain and grain-to-bed collisions are favoured within the flows. These flows tend to evolve into turbidity currents on the lower slope, in response to a marked decrease of slope gradients below ∼ 8°, generating various erosive-depositional features, such as erosive furrows, troughs, channel-levee features and coarse-grained sediment waves. The most active area of the apron lies offshore Sciara del Fuoco (on the NW flank), where a large amount of coarse-grained volcaniclastic material, derived by the persistent Strombolian activity, is collected and deposited by means of high- and low-density turbidity currents on the lower slope down to 2600 m bsl, more than 20 km far from the island. Conversely, other areas are mostly dominated by deposition via settling of suspended sediments, related both to hemipelagic sedimentation and to the dispersion of fine tephras by the prevailing wind and marine currents. Such processes interfinger and overlie in space and time, giving rise to a very complex morpho-sedimentary facies distribution. However, the structural bilateral symmetry of Stromboli volcano allows defining distinct morpho-sedimentary zones, where one (or more) type of processes dominates, and related different stratal architecture of the apron. The unbuttressed portions of the island (NW and SE) are characterized by the emplacement of wide and thick debris avalanche deposits (volume in the order of 1-2 km3 for each event) related to large-scale sector collapses, representing the most important and efficient mass-wasting processes making up the apron. Such deposits are embedded within different volcaniclastic sequences and can be eroded or exhumed by successive gravity flows. The result is a highly complex (both spatially and vertically) succession of facies, where it is often difficult to depict an arranged series of processes. Conversely, on buttressed flanks (SW and NE) a more ordered evolution of processes and deposits making up the apron is observed, giving rise to a less complex apron architecture. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: acoustic facies;  Aeolian islands;  gravity flows;  mass-wasting;  morpho-sedimentary zoning;  seafloor ground-truthing
DOCUMENT TYPE: Article
SOURCE: Scopus

Xiang, Z.a , Yan, Q.a , Yan, Z.a , Wang, Z.b , Wang, T.a , Zhang, Y.b , Qin, X.b 
Facies succession and architecture of volcaniclastic rocks of the Taohekou Formation: Implication for early Silurian volcanism in the north Dabashan area, China
(2010) Acta Geologica Sinica, 84 (3), pp. 311-328. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-78649875972&partnerID=40&md5=cf9e56505d0b1b2bbd4bf48a3ebe0bd9
AFFILIATIONS: Institute of Geology, Chinese Academy of Geological Sciences (CAGS), Beijing, 100037, China; 
Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS), Beijing, 100037, China
ABSTRACT: The Taohekou Formation is constituted with volcanic, volcaniclastic and sedimentary rock. Based on the systematic field work, which including 1:10000 field survey and large scale profile drawing, it could be distinguished twenty-two lithofacies and then grouped into five lithofacies associations from the deposits. According to the comparative studying among different sections, we summarized the generalized succession of the volcanic-sedimentary deposits, which to top is basalt facies (lower is massive basalts, upper is pillow basalts), tuff breccia, resedimented pyroclast-rich (or pyroxene-rich) lapillistone facies, structureless or imbricate tuffaceous conglomerate facies, tuffaceous sandstone facies (locally interbedded with calcarenite), biolithite or mudstone facies. The intensity of volcanism of west area is more powerful than the ones of east area. The type of eruption is Strombolian. The succession of Taohekou Formation, combines with geochemical of volcanic rocks or pyroxene, suggest that the tectonic setting of Taohekou Formation is ocean islands or seamounts, caused by within plate stretching.
AUTHOR KEYWORDS: North daban han;  Sedimentary succession;  Taohekou formation;  Volcanic facies;  Volcaniclastic rocks
DOCUMENT TYPE: Article
SOURCE: Scopus

Bellotti, F.a , Capra, L.b , Sarocchi, D.c , D'Antonio, M.b 
Geostatistics and multivariate analysis as a tool to characterize volcaniclastic deposits: Application to Nevado de Toluca volcano, Mexico
(2010) Journal of Volcanology and Geothermal Research, 191 (1-2), pp. 117-128. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77349118431&partnerID=40&md5=49c5ab958d6687727b5b9d7e8a768897
AFFILIATIONS: Dipartimento di Scienze della Terra-A. Desio, Università degli Studi di Milano, via Mangiagalli 34, 20133 Milano, Italy; 
Centro de Geociencias, UNAM, Campus Juriquilla, 76230 Queretaro, Mexico; 
Inst. de Geología, Fac. de Ingeniería Universidad Autónoma de San Luis Potosí, av. Dr. Manuel Nava N.5 Zona Universitaria, C.P. 78240 San Luis Potosí, Mexico
ABSTRACT: Grain size analysis of volcaniclastic deposits is mainly used to study flow transport and depositional processes, in most cases by comparing some statistical parameters and how they change with distance from the source. In this work the geospatial and multivariate analyses are presented as a strong adaptable geostatistical tool applied to volcaniclastic deposits in order to provide an effective and relatively simple methodology for texture description, deposit discrimination and interpretation of depositional processes. We choose the case of Nevado de Toluca volcano (Mexico) due to existing knowledge of its geological evolution, stratigraphic succession and spatial distribution of volcaniclastic units. Grain size analyses and frequency distribution curves have been carried out to characterize and compare the 28-ka block-and-ash flow deposit associated to a dome destruction episode, and the El Morral debris avalanche deposit originated from the collapse of the south-eastern sector of the volcano. The geostatistical interpolation of sedimentological data allows to realize bidimensional maps draped over the volcano topography, showing the granulometric distribution, sorting and fine material concentration into the whole deposit with respect to topographic changes. In this way, it is possible to analyze a continuous surface of the grain size distribution of volcaniclastic deposits and better understand flow transport processes. The application of multivariate statistic analysis (discriminant function) indicates that this methodology could be useful in discriminating deposits with different origin or different depositional lithofacies within the same deposit. The proposed methodology could be an interesting approach to sustain more classical analysis of volcaniclastic deposits, especially where a clear field classification appears problematic because of a homogeneous texture of the deposits or their scarce and discontinuous outcrops. Our study is an example of the strong versatility of geospatial analysis to provide an effective and relatively clear methodology for the characterization of volcaniclastic deposits. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: geostatistics;  GIS applications;  grain size analyses;  multivariate analysis;  Nevado de Toluca;  volcaniclastic flow characterization
DOCUMENT TYPE: Article
SOURCE: Scopus

Jolly, A.D.a , Sherburn, S.a , Jousset, P.b , Kilgour, G.a 
Eruption source processes derived from seismic and acoustic observations of the 25 September 2007 Ruapehu eruption-North Island, New Zealand
(2010) Journal of Volcanology and Geothermal Research, 191 (1-2), pp. 33-45. Cited 7 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77349118228&partnerID=40&md5=3f1e89e6f25c434ad55d0b9380e0291f
AFFILIATIONS: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; 
BRGM, Development Planning and Natural Hazards Division, 3 Avenue Claude Guillemin, 45060 Orléans, France
ABSTRACT: Mt. Ruapehu erupted on 25 September 2007 at 20:26 PM NZDT (8:26 UT) generating a steam column to about 15,000 ft (4600 m), a directed ballistic and surge deposit of coarse blocks and ash to the north of the Crater Lake, and initiated lahars in the Whangaehu catchment and Whakapapa ski field. The eruption was recorded on three broadband seismometers and two acoustic pressure sensors which indicated broadly coherent waveform characteristics across the network. The eruption had a duration of less than 1 min as indicated by strong seismic and acoustic pulses. The acoustic wave coincided with observed very long-period (VLP) seismic signal (2-25 s period). The acoustic pulse had a positive pressure (indicating an explosion) and travelled at a velocity of ∼ 320 m/s. The syn-eruptive VLP was composed of surface waves having strong radial and transverse components. The immediate aftermath of the eruption produced about 4 min of continued high amplitude spasmodic tremor signals that probably resulted from post-explosion phase associated vent backfill/stabilisation. The eruption was preceded by minor volcano-tectonic earthquakes and tremor bursts which began 10 min before the main eruption. Two smaller VLP signals were associated with these tremor pulses at 20:17 and 20:25. These pre-eruptive VLP signals had particle motions indicating body and surface waves from a sub-surface source region. Modelling of the VLP sources using a 3D finite-difference method shows that that the pre-eruption VLP signals are consistent with a volume fluctuation at 3-7 km depth from a radially symmetric source. The main eruption VLP was consistent with a south and downward directed single force in response to a northward directed jet and northward directed ballistic deposits. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: eruption processes;  finite-difference modelling;  Ruapehu volcano;  seismo-acoustic observations;  VLP
DOCUMENT TYPE: Article
SOURCE: Scopus

Quayle, B.M.a , Mather, T.A.a , Witt, M.L.I.a , Maher, B.A.b , Mitchell, R.b , Martin, R.S.c , Calabrese, S.d  e 
Application and evaluation of biomagnetic and biochemical monitoring of the dispersion and deposition of volcanically-derived particles at Mt. Etna, Italy
(2010) Journal of Volcanology and Geothermal Research, 191 (1-2), pp. 107-116. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77349121582&partnerID=40&md5=489fd65e1b1d09468f62205ffc241ace
AFFILIATIONS: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom; 
Centre for Environmental Magnetism and Palaeomagnetism, Lancaster Environment Centre, University of Lancaster, Farrer Avenue, Lancaster, LA1 4YQ, United Kingdom; 
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom; 
CFTA - Dipt. Chimica e Fisica della Terra e Applicazioni alle Georisorse, Università degli Studi di Palermo, Via Archirafi 36, 90123, Italy; 
INGV - Sezione di Palermo, Via La Malfa 153, 90146, Italy
ABSTRACT: Biomagnetic monitoring, using tree leaves as passive surfaces for particle collection, has been shown to be a promising technique for assessing the dispersion and deposition of particles in the context of anthropogenic pollution. By comparing leaves' magnetic properties with trace metal levels measured in the leaves, we here assess the utility of the biomagnetic technique as a sensitive, fast and inexpensive method for assessment of volcanic plume deposition. Samples of sweet chestnut leaves (Castanea sativa) were collected from the area surrounding Mt. Etna volcano in Sicily during the 2008 growing season when the volcano was displaying mild eruptive activity. Previous work has shown that the trace metal concentrations of these leaves show promise as a bio-indicator of volcanic gas, aerosol and ash deposition on the flanks of Mt. Etna. For 2008, ICP-MS analysis of the elemental abundances within the leaves showed that As, Cd, Cu, Mo, Tl, K, B, Al and Co displayed elevated concentrations downwind of the volcanic source, to the E-ESE, but with overall reduced concentrations relative to 2007. Less explosive activity than 2007 and a broader, more easterly wind field may have distributed the volcanic plume over a wider area, both of which would account for reduced trace element concentrations in 2008. Correspondence of elevated concentrations in both years (2007 and 2008) with their respective wind fields suggests that plume deposition is the controlling factor rather than variability in the soils and that these leaves do indeed have potential as bio-indicators of the plume's dispersion. Magnetic analysis of the leaves shows that the spatial distribution of saturation isothermal remanent magnetisation (SIRM) and magnetic susceptibility (χlf) values display a strong correlation with the wind-influenced plume transport direction for 2008, with elevated concentrations of magnetic minerals on the eastern flanks, in broad agreement with the ICP-MS data. This spatial distribution provides further evidence of plume variability as the main control on the concentrations of magnetic particles on the leaf surfaces and on elemental uptake by the tree and suggests that biomagnetic monitoring may also hold promise as a method of assessing the dispersion and impacts of volcanic plumes. The dominant magnetic mineral on the leaf surfaces is a magnetite-like mineral (contributing &gt; 90% of the SIRM), of coarse, multi-domain (MD) grain size (∼ 5 to 15 μm). A volcanogenic source is most likely, as magnetites from anthropogenic sources are typically an order of magnitude smaller in grain size (∼ 0.1-1 μm). These new results from the use of environmental magnetism on leaves, in a volcanically-affected region, suggest that biomagnetic monitoring offers a new, sensitive and rapid means for the assessment of volcanic plume deposition over wide areas. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Castanea sativa;  magnetic biomonitoring;  Mt. Etna;  plume dispersion;  vegetation
DOCUMENT TYPE: Article
SOURCE: Scopus

Sulpizio, R.a , Bonasia, R.a  b , Dellino, P.a , Mele, D.a , Di Vito, M.A.b , la Volpe, L.a 
The Pomici di Avellino eruption of Somma-Vesuvius (3.9 ka BP). Part II: Sedimentology and physical volcanology of pyroclastic density current deposits
(2010) Bulletin of Volcanology, 72 (5), pp. 559-577. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954142936&partnerID=40&md5=9a784443658be80259ae3d92bfd0006c
AFFILIATIONS: CIRISIVU, c/o Dipartimento Geomineralogico, via Orabona 4, 75125 Bari, Italy; 
Istituto Nazionale di Geofisica e Vulcanologia, Sez. Osservatorio Vesuviano, via Diocleziano 328, 80124 Naples, Italy
ABSTRACT: Pyroclastic density currents (PDCs) generated during the Plinian eruption of the Pomici di Avellino (PdA) of Somma-Vesuvius were investigated through field and laboratory studies, which allowed the detailed reconstruction of their eruptive and transportation dynamics and the calculation of key physical parameters of the currents. PDCs were generated during all the three phases that characterised the eruption, with eruptive dynamics driven by both magmatic and phreatomagmatic fragmentation. Flows generated during phases 1 and 2 (EU1 and EU3pf, magmatic fragmentation) have small dispersal areas and affected only part of the volcano slopes. Lithofacies analysis demonstrates that the flow-boundary zones were dominated by granular-flow regimes, which sometimes show transitions to traction regimes. PDCs generated during eruptive phase 3 (EU5, phreatomagmatic fragmentation) were the most voluminous and widespread in the whole of Somma-Vesuvius' eruptive history, and affected a wide area around the volcano with deposit thicknesses of a few centimetres up to more than 25 km from source. Lithofacies analysis shows that the flow-boundary zones of EU5 PDCs were dominated by granular flows and traction regimes. Deposits of EU5 PDC show strong lithofacies variation northwards, from proximally thick, massive to stratified beds towards dominantly alternating beds of coarse and fine ash in distal reaches. The EU5 lithofacies also show strong lateral variability in proximal areas, passing from the western and northern to the eastern and southern volcano slopes, where the deposits are stacked beds of massive, accretionary lapilli-bearing fine ash. The sedimentological model developed for the PDCs of the PdA eruption explains these strong lithofacies variations in the light of the volcano's morphology at the time of the eruption. In particular, the EU5 PDCs survived to pass over the break in slope between the volcano sides and the surrounding volcaniclastic apron-alluvial plain, with development of new flows from the previously suspended load. Pulses were developed within individual currents, leading to stepwise deposition on both the volcano slopes and the surrounding volcaniclastic apron and alluvial plain. Physical parameters including velocity, density and concentration profile with height were calculated for a flow of the phreatomagmatic phase of the eruption by applying a sedimentological method, and the values of the dynamic pressure were derived. Some hazard considerations are summarised on the assumption that, although not very probable, similar PDCs could develop during future eruptions of Somma-Vesuvius. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Dynamic pressure;  Pomici di Avellino;  Pyroclastic density currents;  Somma-Vesuvius;  Volcanic hazard
DOCUMENT TYPE: Article
SOURCE: Scopus

Fu, G., Hu, M., Yu, D.
Volcanic cap rock type and evaluation of sealing gas ability: an example of Xujiaweizi depression
(2010) Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition), 40 (2), pp. 237-244. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952482588&partnerID=40&md5=fbce40461e9a384064d5cacf7b762e1a
AFFILIATIONS: College of Earth Sciences, Daqing Petroleum Institute, Daqing, Heilongjiang 163318, China
ABSTRACT: By use of drilling, logging and analysis and testing data, the type, feature, identification mark, distribution and sealing ability of volcanic cap rock in Xujiaweizi fault depression and the controlling effect for the accumulation and distribution of gas were studied. It was considered that there were 2 types of volcanic cap rocks in Xujiaweizi fault depression, volcaniclastic rock cap rocks and volcanic lava cap rocks. Volcaniclastic rock cap rocks are mainly tuff and volcanic breccia which are characterized by small resistivity, enlargement of borehole and high interval transit time. Volcanic lava cap rocks are mainly rhyolite, tuff and andesite which are characterized by middle resistivity, normal borehole and low interval transit time. Volcaniclastic rock cap rock and volcanic lava cap rock can be identified respectively by high interval transit time and interval transit time which are lower than 56 μs/ft. Volcaniclastic rock cape rocks are distributed regionally on the top of K1yc1 volcanic rock body, while volcanic lava cap rocks are distributed locally in the volcanic rock body. Sealing gas ability of volcaniclastic rock cap rock is stronger than that of volcanic lava cap rock. Volcaniclastic rock cap rocks controlled the regional accumulation and distribution of gas in volcanic rock in Xujiaweizi fault depression, while volcanic lava cap rocks only controlled the local accumulation and distribution of gas in volcanic rock body.
AUTHOR KEYWORDS: Cap rock;  Interval transit time;  Sealing gas ability;  Songliao basin;  Volcanic lava;  Volcanic rocks;  Volcaniclastic rocks
DOCUMENT TYPE: Article
SOURCE: Scopus

Joannin, S.a  b , Cornée, J.-J.d , Münch, P.c  d , Fornari, M.e , Vasiliev, I.f , Krijgsman, W.f , Nahapetyan, S.g , Gabrielyan, I.h , Ollivier, V.i  j , Roiron, P.k , Chataigner, C.l 
Early Pleistocene climate cycles in continental deposits of the Lesser Caucasus of Armenia inferred from palynology, magnetostratigraphy, and 40Ar/39Ar dating
(2010) Earth and Planetary Science Letters, 291 (1-4), pp. 149-158. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-76149134318&partnerID=40&md5=7a77515637ef0695c79ea36a9adbac76
AFFILIATIONS: UMR CNRS 5125 PEPS, Université Lyon 1, La Doua, bâtiment Géode, F-69622 Villeurbanne cedex, France; 
CNRS-USR 3124 MSHE Ledoux, Rue Mégevand, F-25030 Besançon, France; 
Université de Provence, EA 4234-GSRC, 3 place Victor Hugo, 13331 Marseille cedex, France; 
Géosciences Montpellier, UMR, Université Montpellier 2, place E. Bataillon, 34095 Montpellier Cedex 5, France; 
UMR 6526 Geosciences Azur, Université de Nice Sophia-Antipolis, Parc Valrose, 06108 Nice Cedex 2, France; 
Paleomagnetic Laboratory 'Fort Hoofddijk', Faculty of Earth Sciences, Utrecht University Budapestlaan 17, 3584 CD Utrecht, Netherlands; 
Department of Cartography and Geomorphology, Yerevan State University, Armenia; 
Institute of Botany, National Academy of Sciences of the Republic of Armenia, Armenia; 
Economies, Sociétés et Environnement Préhistorique, UMR 6636, Aix-en-Provence, France; 
Institut Mediterraneen d'Ecologie et de Paleoecologie, UMR 6116, Aix-en-Provence, France; 
Centre de Bio-Archéologie et d'Ecologie, UMR 5059, Montpellier, France; 
Maison de l'Orient, UMR 5133, Lyon, France
ABSTRACT: Plio-Pleistocene diatomitic sequences in the Shamb paleo-lake (South Armenia, Lesser Caucasus) offer a rare opportunity to give new insights on the paleo-climate of Western Asia. We present an integrated palynological, 40Ar/39Ar geochronologic and magnetostratigraphic study for the most complete section in the sedimentary deposits of the Shamb paleo-lake. 40Ar/39Ar dating of two volcaniclastic layers provided ages of 1.24 ± 0.03 and 1.16 ± 0.02 Ma (2:σ). Magnetostratigraphic data show that the entire Shamb section is of reversed polarity which, combined with 40Ar/39Ar dating, suggests that the entire section correlates with part of the Matuyama period (1.785-1.070 Ma). Pollen assemblages and macroremains diversity clearly show an alternation of glacial and interglacial phases. Age calibrations and accumulation rate extrapolation allow a direct correlation of climate changes with the global isotopic curve, and show that the Shamb section probably ranges from approximately 1.300 to 1.080 Ma (marine isotopic stages 40 to 31). The vegetation of the Lesser Caucasus developed in a mosaic pattern in a Pleistocene continental, mostly arid climate, comparable to the present-day climate. The observed vegetation changes record a dominant climate response to the obliquity orbital parameter, but the influence of precession could not be established from the Shamb data. Pollen and macroflora both indicate that glacial periods were cold and dry and that interglacials were warm with local humidity. The Early Pleistocene climatic model for Western Asia is thus similar to the climatic model for the Mediterranean area. © 2010 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: 40Ar/39Ar dating;  Caucasus paleovegetation;  climate;  Early Pleistocene;  magnetostratigraphy;  Western Asia
DOCUMENT TYPE: Article
SOURCE: Scopus

Portner, R.A., Daczko, N.R., Dickinson, J.A.
Vitriclastic lithofacies from Macquarie Island (Southern Ocean): Compositional influence on abyssal eruption explosivity in a dying Miocene spreading ridge
(2010) Bulletin of Volcanology, 72 (2), pp. 165-183. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952886988&partnerID=40&md5=727f223551d5e504171dffc6e8a6fa3d
AFFILIATIONS: GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia
ABSTRACT: Macquarie Island is composed of a complete section of oceanic crust that formed in a slow-spreading mid-ocean ridge 2.0 to 3.5 km below sea level. Vitriclastic facies preserved on the island have both pyroclastic and hyaloclastic characteristics. Monomict hyaloclastic breccia facies are widespread across the island and are predominantly composed of near-primitive (~7.9 wt% MgO) subalkaline/transitional (~0.7 wt% K2O) sideromelane shards and crystalline basalt clasts with low vesicularity (LV, &lt; 15% vesicles). Breccias are thick bedded and structureless with matrix-supported angular pillow fragments, bomb-sized fluidal mini-pillows, and globular glass lapilli. Clasts are lithologically similar to interbedded pillow basalts and laterally grade into fine-grained sandstone facies. These sandstones are normal-graded, well-laminated, thin bedded, and interstratified with red pelagic mudstone. Lithofacies associations indicate that the hyaloclastic breccias were formed proximal to a source vent via quench-fragmentation, and subsequently reworked by ocean-bottom currents into distal epiclastic sandstone facies. During eruption, co-genetic pillow lava and hypabyssal intrusions mingled with the breccia, forming fluidal peperite. Rare polymict pyroclastic facies only occur in the highest stratigraphic levels and are mostly composed of highly vesicular (HV, 15-50% vesicles) sideromelane shards and crystalline basalt clasts with alkaline (~1.0 wt% K2O) fractionated (~6.8% MgO) compositions. Minor lithic grains are composed of subalkaline (~0.7 wt% K2O) to very highly alkaline (~1.7 wt% K2O) LV sideromelane shards, and amphibole-bearing diabase. The pyroclastic facies contains medium to thick beds of lapilli-tuff that exhibit both reverse and normal grading, diffuse lamination, and planar-grain fabric. These beds are locally overlain by thin fine-grained tuff beds entirely composed of cuspate to very thin elongate bubble-wall shards. These characteristics indicate that explosive deep-marine eruptions produced high-density coarse-grained gravity flows that were covered by slower suspension settle-out of delicate bubble-wall shards. Stratigraphic relationships suggest that explosive eruptions started during the waning stages of more alkaline volcanism along the proto-Macquarie spreading center. © 2009 Springer-Verlag.
AUTHOR KEYWORDS: Deep-marine;  Explosive;  Hyaloclastite;  Macquarie Island;  Mid-ocean ridge;  Pyroclastic;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Sheth, H.C.a , Ray, J.S.b , Bhutani, R.c , Kumar, A.b , Awasthi, N.b 
The latest (2008-09) eruption of Barren Island volcano, and some thoughts on its hazards, logistics and geotourism aspects
(2010) Current Science, 98 (5), pp. 620-626. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953345526&partnerID=40&md5=8cb754e81848c01bb4a2ed1577b71f1a
AFFILIATIONS: The Department of Earth Sciences, Indian Institute of Technology Bombay (IITB), Powai, Mumbai 400 076, India; 
Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India; 
The Department of Earth Sciences, Pondicherry University, Puducherry 605 014, India
ABSTRACT: Barren Island, Andaman Sea, is India's only active volcano and is built of lava flows and volcaniclastic deposits of prehistoric through recent ages that are mainly of basalt and basaltic andesite compositions. Historic eruptions occurred during 1787-1832, and it erupted thrice recently in 1991, 1994-95 and 2005-06. A fourth impressive one that might have begun in late 2008 was in full swing in March 2009, with a well-developed lava flow that was entering the sea from a completely different route (north) than all the recent lava flows. We describe and illustrate this new eruption and discuss aspects of hazards, logistics and geotourism potential of this active volcano.
AUTHOR KEYWORDS: Andaman Islands;  Barren island;  Geotourism;  India;  Indian ocean;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Roberts, J., James, L.
Stratigraphic relationships of Carboniferous volcanogenic successions in the Clifton-Carroll block and Werrie Syncline, northern Tamworth Belt, southern New England Orogen
(2010) Australian Journal of Earth Sciences, 57 (2), pp. 193-205. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950927087&partnerID=40&md5=cbd8d0e4559e82fb118db415f403e242
AFFILIATIONS: School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW 2052, Australia
ABSTRACT: Late Carboniferous volcanogenic successions in the Clifton-Carroll block, west of the Werrie Syncline, represent the southernmost extremity of the Willuri Formation, a unit which extends northwards into the Rocky Creek region in northern New South Wales. Two ignimbrites, the Iventure and Tagggarts Mountain Ignimbrite Members, previously named in the Currabubula Formation, are present in the Willuri Formation in the Clifton-Carroll block. The Taggarts Mountain Member extends farther northwards through both Gunnan and Tulcumba Ridges. The western limb of the Werrie Syncline, which is separated from the Clifton-Carroll block by the Kelvin Thrust, contains an Upper Devonian to Upper Carboniferous succession. The largely non-marine, Lower Carboniferous Merlewood Formation is typified by andesite flows, two of which are major, within an area between the Donnellys Gap Fault in the north and Piallaway in the south. The Iventure and Taggarts Mountain Ignimbrite Members in the overlying Upper Carboniferous Currabubula Formation provide a correlation with the Willuri Formation in the Clifton-Carroll block to the west, and the more widespread Taggarts Mountain Ignimbrite Member with the Willuri Formation in Gunnan and Tulcumba Ridges to the north. © 2010 Geological Society of Australia.
AUTHOR KEYWORDS: Carboniferous;  Clifton-Carroll block;  New South Wales;  Stratigraphy;  Volcanics;  Werrie Syncline
DOCUMENT TYPE: Article
SOURCE: Scopus

García Massini, J.L.a , Jacobs, B.F.b , Tabor, N.J.a 
Paleobotany and sedimentology of late oligocene terrestrial strata from the northwestern Ethiopian Plateau
(2010) Palaeontologia Electronica, 13 (1), . Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954640216&partnerID=40&md5=20423f7a3c579d542e51b685cc6346ea
AFFILIATIONS: Roy M. Huffington Department of Earth Sciences, Southern Methodist University, PO Box 750395, Dallas TX 75275-0395, United States; 
Environmental Science Program, Southern Methodist University, PO Box 750395, Dallas, TX 75275-0395, United States
ABSTRACT: This paper describes the sedimentology and paleobotany of a Late Oligocene (27.36 ± 0.11 Ma) succession of volcaniclastic strata from the Margargaria River region, northwestern Ethiopian Plateau. Sedimentology indicates fluvial deposition of clay- and silt-rich strata during the early sedimentary phases, whereas organic-rich deposits and massive and fluvially-reworked ash layers are increasingly more common in the middle and upper parts of the succession, respectively. Periods of interrupted deposition are indicated by three paleosol types present in the basal and middle parts of the succession. Paleobotany documents an exclusively angiosperm flora typical of riparian environments in the lower parts of the succession, and a flora dominated by ferns and a few angiosperm taxa typical of disturbed environments in the middle and upper parts. Sedimentology and paleobotany, combined, indicate a riparian environment inhabited by angiosperms for the lower part of the succession, characterized by rather calm deposition by meandering streams. The middle and upper parts of the succession represent transient environments colonized by pioneer vegetation consisting of a diverse fern community and fewer pioneer angiosperms, characterized by deposition of organic- and ash-rich strata in situ in ephemeral ponds and by small-scale crevasse-like channels and by aereal means on the landscape, respectively. Physiographic changes are interpreted to have resulted directly from the influence of volcanism on the surface environment. In summary, this study shows that the volcanic activity associated with the elevation of the northwestern Ethiopian Plateau during the Oligocene repeatedly influenced the development of plant communities and paleoenvironments, favoring the succession of heterogeneous ecosystems on short temporal and spatial scales. Finally, this study is the first that combines paleobotanical and sedimentological data for paleoenvironmental reconstruction and understanding of plant community dynamics in Paleogene deposits from Africa, and it demonstrates the advantages of a multiproxy approach for assessment of paleoecosystem dynamics on an unstable landscape. © Palaeontological Association March 2010.
AUTHOR KEYWORDS: Angiosperms;  Ethiopia;  Ferns;  Microstratigraphy;  Oligocene;  Paleosols
DOCUMENT TYPE: Article
SOURCE: Scopus

Almeida, R.P.a , Janikian, L.a  b , Fragoso-Cesar, A.R.S.a , Fambrini, G.L.a  c 
The ediacaran to cambrian rift system of southeastern south america: Tectonic implications
(2010) Journal of Geology, 118 (2), pp. 145-161. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77749240281&partnerID=40&md5=e812e397100c578a6fd095610818b6ce
AFFILIATIONS: Instituto de Geociências, Universidade de São Paulo, Cidade Universitária, Rua do Lago, 562, São Paulo, SP CEP 05508-080, Brazil; 
Instituto de Astronomia, Geof́sica e Ciências Atmosféricas Universidade de São Paulo, Cidade Universitária, Rua do Matao, 1226, São Paulo, SP CEP 05508-090, Brazil; 
Instituto de Geociências, Universidade Federal de Pernambuco, Cidade Universitária, Avenida Acadêmico Hélio Ramos s/n, Recife, PE CEP 50740-530, Brazil
ABSTRACT: The tectonic evolution of southeastern South America from the Middle Ediacaran to the Early Cambrian is marked by a series of small fault-bounded siliciclastic and volcaniclastic basins and voluminous coeval granites traditionally associated with the compressional or transpressional tectonics of the late stages of the Pan-African-Brasiliano orogeny. Most existing models consider these basins separately, with distinct tectonic evolutionary histories according to local geological settings. However, new and recently published age constraints, lithological similarities, and structural aspects point to the correlation of all Ediacaran to Cambrian basins in southeastern South America within a common basin system more than 1500 km long. The interpretation of a common origin for all Ediacaran to Cambrian basins of southeastern South America implies that all the different terranes of the Brasiliano orogenic collage in the region were already united in a single plate at approximately 600 Ma. An extensional origin for this basin system is interpreted from the recognition of basin-forming normal faults (later reactivated as strike-slip or inverse) feeding alluvial fans and from expressive basic to acidic volcanic successions in several basins. The occurrence of basic, intermediate, and acidic volcanic rocks and voluminous coeval granites indicates that mantle and crustal fusion were simultaneous with the extensional event. Raised temperatures may have caused the thermal weakening of the lithosphere, enabling both extensional deformation and recurring strike-slip deformation that formed major shear zones in the region. This strike-slip deformation has been mistaken for basin-forming tectonics, but it occurred in the Early Cambrian, after the formation of the basins, and most probably was the result of the far-field propagation of compressional stresses originating in younger collisional orogens at the plate margins. © 2010 by The University of Chicago.
DOCUMENT TYPE: Article
SOURCE: Scopus

Verdecchia, S.O., Baldo, E.G.
Geoquímica y procedencia de los metasedimentos ordovícicos del complejo metamórfico la cébila, provincia de la rioja, Argentina
(2010) Revista Mexicana de Ciencias Geologicas, 27 (1), pp. 97-111. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955997576&partnerID=40&md5=6adee12d69b86fdf53bc5ac2b7e7d554
AFFILIATIONS: Centro de Investigaciones en Ciencias de la Tierra (CICTERRA) - CONICET, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Veléz Sarsfields 1611, C. P. X5016CGA, Córdoba, Argentina
ABSTRACT: The Famatinian orogenic belt of Early Palaeozoic age (Late Cambrian to Middle Ordovician) represents part of the Gondwana southwestern paleo-margin evolution within the pre-Andean basement of central-western Argentina. This belt is composed of igneous rocks with arc signature, a sedimentary succession of marine and volcaniclastic origin and low-to medium-pressure metamorphic units. One of such units is the La Cébila metamorphic complex (LCMC, Early to Middle Ordovician), which includes low - to high-grade metasedimentary successions composed mainly of phyllosilicate-rich (phyllite, mica schists and migmatites) and quartz-feldspar-rich (metapsammite, quartz-mica schists and quartzites) rock types. The current geochemical signal of metasediments from LCMC allows comparing them with at least three primary compositions referring to pelitic, psammites and quartz-psammites lithology types. This suggests that the protolith composition was not substantially altered during the metamorphic event. Low La/Th ratios (2.4-4.5; n = 7) and Hf contents (3.5-11.0; n = 7) , in addition to the absence of detrital zircon ages from the Famatinian volcanic arc (located to the west), suggest a provenance from a source area of felsic composition, consistent with the Pampean basement (Early Cambrian to Middle Cambrian) located to the east (current coordinates). The metasediments from the LCMC are geochemically equivalent to those of the Puncoviscana Formation (Late Neoproterozoic - Early Cambrian), showing minimal differences only in the content of some immobile (e.g., Zr and Ti) and mobile (e.g., K, Sr and Rb) elements. Consequently, major and trace elements are not reliable to differentiate between these two metasedimentary successions.
AUTHOR KEYWORDS: Argentina;  Famatinian orogeny;  Geochemistry;  La cébila metamorphic complex;  Metasediments;  Retro-arc basin
DOCUMENT TYPE: Article
SOURCE: Scopus

Montes, A.D.a , Catalán, J.R.M.b , Mulas, F.B.c 
Role of the Ollo de Sapo massive felsic volcanism of NW Iberia in the Early Ordovician dynamics of northern Gondwana
(2010) Gondwana Research, 17 (2-3), pp. 363-376. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-74449091425&partnerID=40&md5=f9e24eb2fdf0c4f546ffb18de28e0d36
AFFILIATIONS: Instituto Geológico y Minero de España, Azafranal 48, 37001 Salamanca, Spain; 
Departamento de Geología, Universidad de Salamanca, Pl. de la Merced, s/n, 37008 Salamanca, Spain; 
Instituto Geológico y Minero de España, La Calera 1, 28760 Tres Cantos, Spain
ABSTRACT: The Ollo de Sapo Fm. in the Sanabria region of NW Iberia consists of subvolcanic, volcanic and volcano-sedimentary rocks underlying and partly intercalated with Early Ordovician, platform-facies sediments. Granitic plutons of the same age, presently transformed into orthogneisses, are genetically related. The metavolcanic rocks are dacites and rhyolites with potassic and peraluminous character, and volcanic arc signature, possibly inherited from the melting of calc-alkaline crustal material. In the study area, the Ollo de Sapo Fm. is made up of two large superposed volcanic domes separated by a thin screen of contemporaneous metapelites and sandstones. The domes underwent endogenous growth with subvolcanic, phenocryst-rich magma intruding and cooling under a volcanic and volcaniclastic shield. The western dome tapers to the east and underlies the younger eastern dome, suggesting that the whole formation consists of several volcanic edifices replacing each other along the 570 km outcrop belt of the Ollo de Sapo Fm. Two new U-Pb protolith ages of 488 ± 6 Ma and 472 ± 12 Ma match, within error, the known age span for the Ollo de Sapo Fm. in Iberia (495-483 Ma). The younger age dates an augen gneiss at the core of the eastern volcanic dome, whereas the older date comes from the overlying volcanic sequence, suggesting intrusion of the augen gneiss protolith into the overlying volcanic rocks. An incipient rift involving necking of crustal-scale boudinage a few hundred km landward of the edge, but still within the wide passive margin of northern Gondwana may explain the linear distribution of the Ollo de Sapo Fm. and the limited time span of massive volcanism. The heat for crustal melting was probably supplied by mafic magmas intruding or underplatting the lower crust. The Early Ordovician felsic magmatism of NW and Central Iberia seems to form part of a large siliceous province linked to break-up and terrane dispersion of the northern Gondwana realm. © 2009.
AUTHOR KEYWORDS: Metavolcanic rocks;  Northern Gondwana;  Ollo de Sapo Fm.;  Ordovician magmatism;  Variscan belt
DOCUMENT TYPE: Article
SOURCE: Scopus

Schipper, C.I., White, J.D.L.
No depth limit to hydrovolcanic limu o Pele: Analysis of limu from Lō'ihi Seamount, Hawai'i
(2010) Bulletin of Volcanology, 72 (2), pp. 149-164. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952878405&partnerID=40&md5=105a76f2a73a59053358f2ef0e413918
AFFILIATIONS: Geology Department, University of Otago, PO Box 56, Leith St., Dunedin 9016, New Zealand
ABSTRACT: Deep-sea limu o Pele are shards of basaltic glass commonly described as "bubble walls." When first identified they were inferred to form in submarine fire fountains, but were then reinterpreted as the products of hydrovolcanic volcanism, formed when submarine lava flows entrapped and vaporised seawater. Limu discovered below the c 3 km critical depth of seawater, where superheated water exists as a supercritical fluid instead of a vapour, led to the hydrovolcanic model of limu o Pele formation being discarded in favour of a magmatic CO2-driven, "strombolian-like" model. This revised magmatic mechanism has been widely accepted by the scientific community. We describe a newly discovered limu o Pele-rich deposit at ~1,052 mbsl on the northeast summit plateau region of Lō'ihi Seamount, Hawai'i. The limu at this site is concentrated in a chemically monomict ash lens interbedded with thin lava sheets that are separated from overlying volcaniclastic material by a discontinuity. The geometry and geochemistry of the deposit provide compelling evidence for a hydrovolcanic, sheet flow-related origin. The exceptional abundance and preservation of limu at this site allows 4 morphologic subtypes of limu- thin film, plateau-border, convex film, and Pele's hair- to be identified and linked to portions of the isolated rupturing bubbles from which they are derived. We extend our discussion to beyond this new Lō'ihi deposit, by including a review of limu o Pele occurrences and thermodynamic considerations that demonstrate the hydrovolcanic model of limu formation to be more tenable than the magmatic model at all depths, including below the critical depth of seawater. © 2009 Springer-Verlag.
AUTHOR KEYWORDS: Hawaii;  Hydrovolcanic;  Limu;  Loihi;  Pyroclastic;  Subaqueous
DOCUMENT TYPE: Article
SOURCE: Scopus

Castruccio, A.a , Clavero, J.b , Rivera, A.c 
Comparative study of lahars generated by the 1961 and 1971 eruptions of Calbuco and Villarrica volcanoes, Southern Andes of Chile
(2010) Journal of Volcanology and Geothermal Research, 190 (3-4), pp. 297-311. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75949090599&partnerID=40&md5=1cec74519ab57e129b9b708e395dd40d
AFFILIATIONS: Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile; 
Servicio Nacional de Geología y Minería, Ave. Santa Maria 0104, Casilla 10465, Santiago, Chile; 
Centro de Estudios Científicos, Ave. Arturo Prat 514, Casilla 1469, Valdivia, Chile
ABSTRACT: The Villarrica and Calbuco volcanoes, of the Andean Southern Volcanic Zone, are two of the most active volcanoes in Chile and have erupted several times in the XX century. The 1961 eruption at Calbuco volcano generated lahars on the North, East and Southern flanks, while the 1971 eruption at Villarrica volcano generated lahars in almost all the drainages towards the north, west and south of the volcano. The deposits from these eruptions in the Voipir and Chaillupén River (Villarrica) and the Tepú River (Calbuco) are studied. The 1971 lahar deposits on Villarrica volcano show a great number of internal structures such as lamination, lenses, grading of larger clasts and a great abundance of large floating blocks on top of the deposits. The granulometry can be unimodal or bimodal with less than 5% by weight of silt + clay material. SEM images reveal a great variety of forms and compositions of clasts. The 1961 lahar deposits on Calbuco volcano have a scarce number of internal structures, steeper margins and features of hot emplacement such as semi-carbonized vegetal rests, segregation pipes and a more consolidated matrix. The granulometry usually is bimodal with great quantities of silt + clay material (> 10% by weight). SEM images show a uniformity of composition and forms of clasts. Differences on deposits reveal different dynamics on both lahars. The Villarrica lahar was generated by sudden melt of ice and snow during the paroxysmal phase of the 1971 eruption, when a high fountain of lava was formed. The melted water flowed down on the flanks of the volcano and incorporated sediments to become transition flows, highly energetic and were emplaced incrementally. Dilution of the flows occurs when the lahars reached unconfined and flatter areas. In cases where the lahar flow found large water streams, dilution is enhanced. The Calbuco lahars were generated by the dilution of block and ash pyroclastic flows by flowing over the ice or snow or by entering active rivers, transforming to debris flows. The differences on dynamics of both flows show the importance to understand initiation processes of lahars in order to make better hazard assessment due to laharics flows. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Calbuco volcano;  debris flow;  Lahar;  Southern Andes;  Villarrica volcano
DOCUMENT TYPE: Article
SOURCE: Scopus

Kratzmann, D.J.a , Carey, S.N.a , Fero, J.a , Scasso, R.A.b , Naranjo, J.-A.c 
Simulations of tephra dispersal from the 1991 explosive eruptions of Hudson volcano, Chile
(2010) Journal of Volcanology and Geothermal Research, 190 (3-4), pp. 337-352. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75949105383&partnerID=40&md5=b5e78f36017ffc7595515affa6c72a8b
AFFILIATIONS: Graduate School of Oceanography, Univ. of Rhode Island, South Ferry Rd, Narragansett, RI 02882, United States; 
Departamento de Geología, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria Pab. II, 1428 Buenos Aires, Argentina; 
Servicio Nacional de Geología y Minería, Casilla, 10465, Santiago, Chile
ABSTRACT: The 1991 explosive eruptions of Hudson volcano in southern Chile produced 2.7 km3 (dense rock equivalent) of basalt and trachyandesite tephra during the period August 8-15. The initial basaltic phase (phase I, August 8-9) produced a maximum column height of 12 km above sea level (ASL) and tephra fallout was directed to the north and northeast by the prevailing winds. The paroxysmal trachyandesitic phase (phase II, August 12-15) involved at least three separate events with a maximum ∼ 18-km-high (ASL) eruption column inferred from satellite temperature data. During the initial 24 h of this phase the plume was advected almost directly south, before swinging towards the east as the wind changed direction. The plume was ultimately directed to the southeast and stayed relatively fixed at this bearing for the remainder of the eruption. These temporal variations in the main dispersal direction during the earlier stages of the phase II eruption produced a much wider overall deposit than would be expected from a plume with a relatively fixed transport direction (e.g., latter stages of phase II). The Lagrangian ash tracking model PUFF was utilized to simulate the 1991 explosive eruptions and was able to successfully reproduce the aerial distribution and temporal evolution of the plumes. The optimal agreement between the observed and simulated plumes occurs when the highest concentration of ash particles coincides with the tropopause, a height that is typically lower than the maximum observed column heights for the 1991 eruptions. Gravitational settling of the laterally spreading umbrella region (e.g., Pinatubo 1991) may result in the concentration of ash at this level. This may account for differences in column height estimates between ground- or satellite-based and lithic-based models. The plume associated with the paroxysmal phase (August 12-15, 1991) produced a multilayered deposit composed of alternating layers of fine ash and pumice lapilli. The highly stratified nature of the fall deposit is likely the result of multiple eruptive events coupled with a time varying wind field. A strongly changing wind direction that occurred during the earlier stages of the paroxysmal eruption could have produced variations in the dominant grain size being deposited between fine ash and pumice lapilli during individual eruptive sequences. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Hudson volcano;  PUFF simulations;  Southern Volcanic Zone;  tephra dispersal;  tropospheric transport;  wandering plume
DOCUMENT TYPE: Article
SOURCE: Scopus

Vogel, S.a , Märker, M.b  c 
Reconstructing the Roman topography and environmental features of the Sarno River Plain (Italy) before the AD 79 eruption of Somma-Vesuvius
(2010) Geomorphology, 115 (1-2), pp. 67-77. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-73849116107&partnerID=40&md5=a3c44963c385b108d89566c2cdee478d
AFFILIATIONS: German Archaeological Institute, Podbielskiallee 69-71, D-14195 Berlin, Germany; 
Heidelberg Academy of Sciences and Humanities, University of Tübingen, Rümelinstraße 19-23, D-72070 Tübingen, Germany; 
Department of Soil Science and Plant Nutrition, University of Florence, Italy
ABSTRACT: A methodology was developed to reconstruct the Roman topography and environmental features of the Sarno River plain, Italy, before the AD 79 eruption of the Somma-Vesuvius volcanic complex. We collected, localized and digitized more than 1800 core drilling data to gain a representative network of stratigraphical information covering the entire plain. Besides other stratigraphical data including the characteristics of the pre-AD 79 stratum, the depth to the pre-AD 79 surface was identified from the available drilling documentations. Instead of a simple interpolation method, we used a machine based learning approach based on classification and regression trees to reconstruct the pre-AD 79 topography. We hypothesize that the present-day topography reflects the ancient topography and related surface processes, because volcanic deposits from the AD 79 eruption coated the ancient landscape. Thus, ancient physiographic elements of the Sarno River plain are still recognizable in the present-day topography. Therefore, a high-resolution, present-day digital elevation model (DEM) was generated. A detailed terrain analysis yielded 15 different primary and secondary topographic indices. Subsequently, a classification and regression model was applied to predict the depth of the pre-AD 79 surface combining present-day topographic indices with other physiographic data. This model was calibrated with the measured depth of the pre-AD 79 surface. The resulting pre-AD 79 DEM was compared with the classified characteristic of the pre-AD 79 stratum, identified from the drilling documentations. This allowed the reconstruction of pre-AD 79 environmental features of the Sarno River plain such as the ancient coastline, the paleo-course of the Sarno River and its floodplain. To the knowledge of the authors, it is the first time that the pre-AD 79 topography of the Sarno River plain was systematically reconstructed using a detailed database and sophisticated data mining technologies. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Landscape reconstruction;  Modeling;  Paleo-environment;  Paleo-topography;  Sarno River plain;  Somma-Vesuvius
DOCUMENT TYPE: Article
SOURCE: Scopus

Buse, B.a , Schumacher, J.C.a , Sparks, R.S.J.a , Field, M.b 
Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: Insights into hydrothermal metamorphism in kimberlite pipes
(2010) Contributions to Mineralogy and Petrology, 160 (4), pp. 533-550. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956403269&partnerID=40&md5=04f6b1b24b3587fde0a04a304da973da
AFFILIATIONS: Department of Earth Sciences, University of Bristol, Bristol, United Kingdom; 
DiaKim Consulting Limited, Wookey Hole, Wells, United Kingdom
ABSTRACT: Metamorphic assemblages within Karoo basalt xenoliths, found within volcaniclastic kimberlite of the B/K9 pipe, Damtshaa, Botswana, constrain conditions of kimberlite alteration. Bultfonteinite and chlorite partially replace the original augite-plagioclase assemblage, driven by the serpentinisation of the kimberlite creating strong chemical potential gradients for Si and Mg. Hydrogarnet and serpentine replace these earlier metamorphic assemblages as the deposits cool. The bultfonteinite (ideally Ca2SiO2[OH,F]4) and hydrogarnet assemblages require a water-rich fluid containing F-, and imply hydrothermal alteration dominated by external fluids rather than autometamorphism from deuteric fluids. Bultfonteinite and hydrogarnet are estimated to form at temperatures of ca. 350-250°C, which are similar to those for serpentinisation. Alteration within the B/K9 kimberlite predominantly occurs between 250 and 400°C. We attribute these conditions to increased efficiency of mass transfer and chemical reactions below the critical point of water and a consequence of volume-increasing serpentinisation and metasomatic reactions that take place over this temperature range. A comparison of the B/K9 kimberlite with kimberlites from Venetia, South Africa suggests that the composition and mineralogy of included xenoliths affects the alteration assemblages within kimberlite deposits. © 2010 Springer-Verlag.
AUTHOR KEYWORDS: Hydrothermal metamorphism;  Kimberlite;  Post-emplacement;  Serpentinisation;  Xenolith
DOCUMENT TYPE: Article
SOURCE: Scopus

Tamura, Y.a , Ishizuka, O.b , Aoike, K.c , Kawate, S.d , Kawabata, H.a , Chang, Q.a , Saito, S.a , Tatsumi, Y.a , Arima, M.e , Takahashi, M.f , Kanamaru, T.f , Kodaira, S.a , Fiske, R.S.g 
Missing oligocene crust of the Izu-Bonin Arc: Consumed or rejuvenated during collision?
(2010) Journal of Petrology, 51 (4), art. no. egq002, pp. 823-846. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952727351&partnerID=40&md5=00c57ea24f8265c370c9a7ce0f20ba83
AFFILIATIONS: Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan; 
Institute of Geoscience, Geological Survey of Japan/AIST, Tsukuba 305-8567, Japan; 
Center For Deep Earth Exploration (CDEX), Japan Agency For marine-Earth science and Technology, Yokohama 236-0001, Japan; 
Musashi High School, Tokyo 176-8535, Japan; 
Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama 240-8501, Japan; 
Institute of Natural Sciences, Nihon University, Tokyo 156-8550, Japan; 
Smithsonian Institution, NMNH MRC-119, Washington, DC 20013-7012, United States
ABSTRACT: The ~50 Myr old Izu-Bonin-Mariana (IBM) arc consists mostly of Oligocene middle and lower crust that underlies the upper crust; these units are in turn covered by Quaternary volcanic rocks. Seismic imaging, forearc geology, Ocean Drilling Program drilling and magnetic anomalies suggest that most IBM arc crust was created in Eocene-Oligocene times. However, remnants of this old crust have never been found at the northern end of the arc, where it is colliding with the Honshu arc (Izu collision zone).Two batholiths in this collision zone (theTanzawa tonalites and the Kofu Granitic Complex) were emplaced during the Miocene (4-17 Ma). Major elements, Zr/Y, rare earth element ratios and normalized abundance patterns, and Sr-Nd isotopic data indicate that these plutonic bodies are compositionally similar to the Oligocene IBM volcanic rocks, and that they are dissimilar to the Miocene, Pliocene and Quaternary IBM lavas and volcaniclastic rocks. We suggest that the Miocene plutonic rocks in the Izu collision zone were derived from partially melted Oligocene middle crust. A model is proposed in which IBMarc middle crust in the collision zone was partially melted during the collision and then intruded into the overlying upper crust of the Honshu and IBMarcs.This resulted in the complete loss of chronological information related to their original source. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org.
AUTHOR KEYWORDS: Collision zone;  Granite;  IBM arc;  Oligocene;  Remobilization;  Tonalite
DOCUMENT TYPE: Article
SOURCE: Scopus

Rotonda, T.a , Tommasi, P.b , Boldini, D.c 
Geomechanical characterization of the volcaniclastic material involved in the 2002 landslides at Stromboli
(2010) Journal of Geotechnical and Geoenvironmental Engineering, 136 (2), art. no. 012002QGT, pp. 389-401. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953247495&partnerID=40&md5=e348bb95eabc37295601c2e33a6abf86
AFFILIATIONS: Dept. of Structural and Geotechnical Engineering, Sapienza Univ. of Rome, Via Eudossiana 18, 00184 Rome, Italy; 
National Research Council, Institute for Geo-Engineering and Environmental Geology, Via Eudossiana 18, 00184 Rome, Italy; 
Dept. of Chemical, Mining and Environmental Engineering, Univ. of Bologna, Via Terracini 28, 40131 Bologna, Italy
ABSTRACT: During the 2002 eruption, the NW flank of Stromboli volcano (Southern Italy) experienced large landslides that produced tsunami waves with a maximum runup of 10 m in height. This paper focuses on the geomechanical behavior of the loose volcaniclastic layers, the weakest component of the deposit forming the volcano flank. Tests on the coarse-grained volcaniclastic soil and on the rock material forming the grains were conducted in dry conditions, a feature of the subaerial slope. The rock material, in spite of its high porosity, exhibits relatively high stiffness and strength due to the remarkable continuity of the solid skeleton. Accordingly, the volcaniclastic soil is characterized by high shear strength. During shear tests, however, significant grain crushing occurs, which partly explains the nonlinear shear strength envelope and the strain softening associated with contractive behavior. Grain crushing was also found to affect compressibility and its time dependency, investigated under oedometric conditions. © 2010 ASCE.
AUTHOR KEYWORDS: Laboratory test;  Landslides;  Shear strength;  Volcanic rocks;  Volcaniclastic soil
DOCUMENT TYPE: Article
SOURCE: Scopus

Gardner, J.N.a , Goff, F.b , Kelley, S.c , Jacobs, E.d 
Rhyolites and associated deposits of the Valles-Toledo caldera complex
(2010) New Mexico Geology, 32 (1), pp. 3-18. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950195976&partnerID=40&md5=89690da3b273a5ebae20a6d7ea8a9343
AFFILIATIONS: 14170 Highway 4, Jemez Springs NM 87025, United States; 
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 8713, United States; 
New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro NM 87801, United States; 
3007 Villa Street, Los Alamos, NM 87544, United States
ABSTRACT: Several decades of focused studies on the Valles-Toledo caldera complex and the Jemez Mountains in northern New Mexico have brought about new understanding of the relations of stratigraphic units that record the complex's evolution. We present here a revision of the formal stratigraphic nomenclature for the Quaternary Tewa Group, an established stratigraphic unit that includes the volcanic and volcaniclastic deposits of the caldera complex. We propose 11 completely new units of member rank, with descriptions of lithology, contact relations, distribution, and type areas. These new members are parts of the Bandelier Tuff, Cerro Toledo, and Valles Rhyolite Formations, and serve to depict the magmatic and geomorphic evolution of the area during and following each of two major caldera-forming episodes. With results from mapping efforts in the Jemez Mountains revealing the broad implications and interrelations of some established units, we redefine one formation (Cerro Toledo Rhyolite) and demote three formal members (El Cajete, Battleship Rock, and Banco Bonito) to bed or flow rank. Because it has been shown repeatedly in published works that one formation (Cerro Rubio Quartz Latite) was originally defined based on erroneous relations, we propose its formal abandonment. Additionally, we propose formal abandonment of one established member (Valle Grande Member of the Valles Rhyolite) because of lack of utility and widespread disuse. Our proposed revisions embody the practices of geologic mappers, and serve to better clarify relations of volcanic and volcaniclastic rocks through the evolution of the Valles-Toledo caldera complex. The new formal stratigraphy that we propose will provide a flexible but robust framework for on-going and future research in the Valles-Toledo caldera complex.
DOCUMENT TYPE: Article
SOURCE: Scopus

Rogers, J.J.W., Coleman, D.S.
Evolution of the slate belt in north Carolina
(2010) Southeastern Geology, 47 (1), pp. 1-13. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950307649&partnerID=40&md5=32654b6c9d4e215aaa729c7740aa0591
AFFILIATIONS: Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, United States
ABSTRACT: The slate belt in North Carolina contains two bimodal volcanic and volcaniclastic rock sequences. The Virgilina sequence comprises most of the slate belt, and its development was complete by about 600 Ma. The Albemarle sequence is in the Uwharrie Mountains, and its evolution spanned the Precambrian-Cambrian boundary. Compositions of both sequences show that they were formed above subduction zones. TDM values about 100 m.y. older than eruption ages suggest that Virgilina rocks formed in a primitive intra-oceanic island arc. Conversely, TDM ages several hundred m.y. older than eruption ages are consistent with formation of the Albemarle rocks above a subduction zone on a newly formed continental margin. We propose: the Albemarle sequence formed along the continental margin of South America after it rifted from Rodinia; the Albemarle sequence then rifted away from South America; the Albemarle and Virgilina sequences joined to form the slate belt in the ocean between South America and North America; the slate belt then accreted to North America by subduction of the intervening ocean beneath the slate belt.
DOCUMENT TYPE: Article
SOURCE: Scopus

Lopez-Loera, H.a , Urrutia-Fucugauchi, J.b , Alva-Valdivia, L.M.b 
Magnetic characteristics of fracture zones and constraints on the subsurface structure of the Colima Volcanic Complex, western Mexico
(2010) Geosphere, 6 (1), pp. 35-46. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954019636&partnerID=40&md5=3c63aa342f16f6ab83e86429a04c8232
AFFILIATIONS: Instituto Potosino de Investigación Científica y Tecnológica, Camino a la Presa San José 2055, Lomas 4a Sección, 78216, San Luis Potosí, S.L.P., Mexico; 
Laboratorio de Paleomagnetismo y Geofísica Nuclear, Instituto de Geofísica, Universidad Nacional Autonoma de México, Coyoacán 04510 Mexico D.F., Mexico
ABSTRACT: Detailed magnetic anomaly surveys over the central and southern sector of the Colima rift, western Mexico, are used to investigate the subsurface structure and faults and/or fractures in the volcanic terrains formed by activity in the Colima volcanic complex (CVC). The CVC is located within the large north-south Colima rift in western Mexico. The Colima rift is a major active tectonic structure, trending perpendicular to the Middle America Trench and related to subduction of the Rivera and Cocos plates. Volcanic activity in the CVC has migrated southward toward the trench. Analyses of faults and recent deformation in the CVC and Colima rift are of major interest in volcano-tectonic studies and for hazard assessment. Structural analyses and fault mapping, however, are difficult because young volcanic and pyroclastic rocks obscure structural features and stratigraphy. Most of the southern Colima rift is covered by volcanic avalanches and volcaniclastic units, which have resulted in resurfacing of the volcanic terrains. Here we show that magnetic anomalies permit identification of faults and mapping of volcano-sedimentary and volcanic units. Total magnetic field measurements spaced every 0.5 km along 8 profiles, with an overall length of 284.5 km and covering the CVC sector of the Colima rift, have been obtained. We recognize fractures and fault zones of local and regional character from their characteristic magnetic anomaly response. Large mapped structures include the north-south Montitlan, northeast-southwest La Lumbre, and east-west La Escondida faults, which can be traced across the area from the magnetic profiles. Fault magnetic anomalies are modeled by lateral contrasts in terms of step models assuming thin dipping elongated zones along the fault planes. The study shows that faults in the CVC volcanic terrain can be investigated by magnetic surveying. © 2010 by Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Schwarz-Schampera, U.a , Terblanche, H.b , Oberthür, T.a 
Volcanic-hosted massive sulfide deposits in the Murchison greenstone belt, South Africa
(2010) Mineralium Deposita, 45 (2), pp. 113-145. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954032781&partnerID=40&md5=2bae37804cc3cb39ea73e44dd2b8d657
AFFILIATIONS: BGR, Hannover, Germany; 
METOREX Ltd., Rosebank, South Africa
ABSTRACT: The Archean Murchison greenstone belt, Limpopo Province, South Africa, represents a rifted epicontinental arc sequence containing the largest volcanic-hosted massive sulfide (VMS) district in Southern Africa. The so-called Cu-Zn line is host to 12 deposits of massive sulfide mineralization including: Maranda J, LCZ, Romotshidi, Mon Desir, Solomons, and Mashawa with a total tonnage of three million metric tons of very high grade Zn, subordinate Cu, and variable Pb and Au ore. The deposits developed during initial phases of highly evolved felsic volcanism between 2,974.8 ± 3.6 and 2,963.2 ± 6.4 Ma and are closely associated with quartz porphyritic rhyolite domes. Elevated heat supply ensured regional hydrothermal convection along the entire rift. Recurrent volcanism resulted in frequent disruption of hydrothermal discharge and relative short-lived episodes of hydrothermal activity, probably responsible for the small size of the deposits. Stable thermal conditions led to the development of mature hydrothermal vent fields from focused fluid discharge and sulfide precipitation within thin layers of felsic volcaniclastic rocks. Two main ore suites occur in the massive sulfide deposits of the "Cu-Zn line": (1) a low-temperature venting, polymetallic assemblage of Zn, Pb, Sb, As, Cd, Te, Bi, Sn, ±In, ±Au, ±Mo occurring in the pyrite- and sphalerite-dominated ore types and (2) a higher temperature suite of Cu, Ag, Au, Se, In, Co, Ni is associated with chalcopyrite-bearing ores. Sphalerite ore, mineralogy, and geochemical composition attest to hydrothermal activity at relatively low temperatures of ≤250 °C for the entire rift, with short-lived pulses of higher temperature upflow, reflected by proportions of Zn-rich versus Cu-rich deposits. Major- and trace-metal composition of the deposits and Pb isotope signatures reflect the highly evolved felsic source rock composition. Geological setting, host rock composition, and metallogenesis share many similarities not only with Archean VMS districts in Canada and Australia but also with recent arc-back-arc systems on the modern seafloor where fragments of continental crust and areas of elevated heat flow are involved in petrogenetic and associated metallogenic processes. © 2009 Springer-Verlag.
AUTHOR KEYWORDS: Archean;  Kaapvaal craton;  Murchison greenstone belt;  South Africa;  Volcanic-hosted massive sulfide deposits
DOCUMENT TYPE: Article
SOURCE: Scopus

Loizeau, D.a  b , Mangold, N.c , Poulet, F.a , Ansan, V.c , Hauber, E.d , Bibring, J.-P.a , Gondet, B.a , Langevin, Y.a , Masson, P.b , Neukum, G.e 
Stratigraphy in the Mawrth Vallis region through OMEGA, HRSC color imagery and DTM
(2010) Icarus, 205 (2), pp. 396-418. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75449098834&partnerID=40&md5=18f27b0c1137a2545319e82ad081b4f5
AFFILIATIONS: IAS-UMR8617, Université Paris-Sud XI, Bat. 121, 91405 Orsay cedex, France; 
IDES, UMR8148, Université Paris-Sud XI, Bat. 509, 91405 Orsay cedex, France; 
LPGN, UMR6112, Université de Nantes, 2 rue de la Houssiniere, 44322 Nantes cedex 3, France; 
Institute for Planetary Exploration, DLR, Rutherfordstr. 2, 12489 Berlin, Germany; 
Freie Universitaet Berlin, FR Planetologie und Fernerkundung, Malteserstr. 74-100, 12249 Berlin, Germany
ABSTRACT: The Mawrth Vallis region contains an extensive (at least 300 km × 400 km) and thick (≥300 m), finely layered (at meter scale), clay-rich unit detected by OMEGA. We use OMEGA, HRSC DTMs derived from stereoscopic imagery, HRSC color imagery and high resolution imagery such as MOC, CTX and HiRISE to characterize the geometry and the composition of the clay-rich unit at the regional scale. Our results show that the clay-bearing unit can be divided into sub-units on the basis of differences in color and composition. In false-color visible imagery, alternating white/bluish and orange/red colored units correspond to a compositional succession of, respectively, Al- and Fe- or Mg-phyllosilicate rich material. Geological cross-sections are presented along the principal outcrops of the region in order to define the stratigraphy of these sub-units. This method shows that the dips of the sub-units are frequently close to the slopes of the present topography, except for scarps visible at the dichotomy boundary, inside impact craters walls, and outcrops inside Mawrth Vallis. In addition to the Al- and Fe- or Mg-phyllosilicate rich sub-units, an altered surface is identified as the lower basement unit. We propose two possible end-member scenarios to explain the derived stratigraphy: (1) alteration of volcaniclastic, aeolian or aqueous layered deposits of various compositions by groundwater, resulting in distinct altered rocks; or (2) Alteration coeval with the deposition of sediments under varying chemical conditions, in wet pedodiagenetic environment. © 2009 Elsevier Inc. All rights reserved.
AUTHOR KEYWORDS: Infrared observations;  Mars, Surface;  Mineralogy;  Spectroscopy
DOCUMENT TYPE: Article
SOURCE: Scopus

Paulatto, M.a , Minshull, T.A.a , Baptie, B.b , Dean, S.a , Hammond, J.O.S.c , Henstock, T.a , Kenedi, C.L.d , Kiddle, E.J.c , Malin, P.d , Peirce, C.e , Ryan, G.d  f , Shalev, E.d , Sparks, R.S.J.c , Voight, B.g 
Upper crustal structure of an active volcano from refraction/reflection tomography, Montserrat, Lesser Antilles
(2010) Geophysical Journal International, 180 (2), pp. 685-696. Cited 10 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-74549202613&partnerID=40&md5=75718dd7cce826db2274852a5317c8a9
AFFILIATIONS: National Oceanography Centre, Southampton SO14 3ZH, United Kingdom; 
British Geological Survey, West Mains Road, Edinburgh EH9 3LA, United Kingdom; 
Department of Earth Science, University of Bristol, Queen's Road, Bristol BS8 1RJ, United Kingdom; 
Institute of Earth Science and Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; 
Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom; 
Montserrat Volcano Observatory, Flemmings, Montserrat, Montserrat; 
Department of Geosciences, Penn State University, University Park, 503 Deike Building, PA 16802, United States
ABSTRACT: To better understand the volcanic phenomena acting on Montserrat, the SEA-CALIPSO seismic experiment (Seismic Experiment with Airgun-source - Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory) was conducted in 2007 December with the aim of imaging the upper crust and the magmatic system feeding the active Soufriére Hills Volcano. The 3-D survey covered an area of about 50 × 40 km and involved the deployment of 247 land stations and ocean-bottom seismometers (OBSs). A subset of the data, recorded by four OBSs and four land stations on a southeast to northwest line, has been analysed, and traveltimes have been inverted to obtain a 2-D seismic velocity model through the island. Inverted phases include crustal and sediment P waves and wide-angle reflections. The resulting velocity model reveals the presence of a high velocity body (3.5-5.5 km s-1) beneath the island, with highest velocities beneath the Soufriére and Centre Hills, corresponding primarily to the cores of these volcanic edifices, built of a pile of andesite lava domes and subsequent intrusions. In the offshore region, velocities in the surficial sediment layer vary from 1.5 to 3.0 km s-1, consistent with a mainly calcareous and volcaniclastic composition. A wide-angle reflector is observed at a depth of ∼1200 m below the seabed, and appears to deepen beneath the island. The upper crust beneath this reflector has velocities of 4.0-6.0 km s-1 and is inferred to correspond to plutonic and hypabyssal rocks and sedimentary material of the old arc. The high velocity region beneath the island, extends into the crust to a depth of at least 5 km, and is believed to be caused by an intrusive complex, possibly of intermediate composition. A low velocity zone, as would be expected in the presence of an active magma chamber, was not observed perhaps due to the limited resolution beneath ∼5 km depth. Our results so far provide the first wide-angle seismic constraints on the upper crustal structure of the island to a depth of 10 km, and will help understanding the processes that drive volcanism at Montserrat and other island arc volcanoes. © 2009 The Authors Journal compilation © 2009 RAS.
AUTHOR KEYWORDS: Controlled source seismology;  Crustal structure;  Seismic tomography;  Volcanic arc processes;  Volcano monitoring;  Volcano seismology
DOCUMENT TYPE: Article
SOURCE: Scopus

Greene, A.R.a , Scoates, J.S.a , Weis, D.a , Katvala, E.C.b , Israel, S.c , Nixon, G.T.d 
The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau
(2010) Geosphere, 6 (1), pp. 47-73. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954203592&partnerID=40&md5=1edd613597b656b2d47ec334ba5d094d
AFFILIATIONS: Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada; 
Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N1N4, Canada; 
Yukon Geological Survey, 2099-2nd Ave, Whitehorse, Yukon Y1A2C6, Canada; 
British Columbia Geological Survey, P.O. Box 9320, Station Provincial Government, Canada
ABSTRACT: The accreted Wrangellia flood basalts and associated sedimentary rocks that compose the prevolcanic and postvolcanic stratigraphy provide an unparalleled view of the architecture, eruptive environment, and accumulation and subsidence history of an oceanic plateau. This Triassic large igneous province extends for ~2300 km in the Pacific Northwest of North America, from central Alaska and western Yukon (Nikolai Formation) to Vancouver Island (Karmutsen Formation), and contains exposures of submarine and subaerial volcanic rocks representing composite stratigraphic thicknesses of 3.5-6 km. Here we provide a model for the construction of the Wrangellia oceanic plateau using the following information and visualization tools: (1) stratigraphic summaries for different areas of Wrangellia; (2) new 40Ar/39Ar geochronology results; (3) compilation and assessment of geochronology and biostratigraphy for Wrangellia; (4) compiled digital geologic maps; (5) an online photographic archive of field relationships; and (6) a Google Earth file showing the mapped extent of Wrangellia flood basalts and linked field photographs. Based on combined radiometric (U-Pb, 40Ar/39Ar, K-Ar), paleontological, and magnetostratigraphic age constraints, the Wrangellia flood basalts were emplaced during a single phase of tholeiitic volcanism ca. 230-225 Ma, and possibly within as few as 2 Myr, onto preexisting submerged arc crust. There are distinct differences in volcanic stratigraphy and basement composition between Northern and Southern Wrangellia. On Vancouver Island, ~6 km of high-Ti basalts, with minor amounts of picrites, record an emergent sequence of pillow basalt, pillow breccia and hyaloclastite, and subaerial flows that overlie Devonian-Mississippian (ca. 380-355 Ma) island arc rocks and Mississippian-Permian marine sedimentary strata. In contrast, Alaska and Yukon contain 1-3.5-km-thick sequences of mostly subaerial high-Ti basalt flows, with low-Ti basalt and submarine pillow basalts in the lowest parts of the stratigraphy, that overlie Pennsylvanian-Permian (312-280 Ma) volcanic and sedimentary rocks. Subsidence of the entire plateau occurred during and after volcanism, based on late-stage interflow sedimentary lenses in the upper stratigraphic levels and the presence of hundreds of meters to &gt;1000 m of overlying marine sedimentary rocks, predominantly limestone. The main factors that controlled the resulting volcanic architecture of the Wrangellia oceanic plateau include high effusion rates and the formation of extensive compound flow fields from low-viscosity, high-temperature tholeiitic basalts, sill-dominated feeder systems, limited repose time between flows (absence of weathering, erosion, sedimentation), submarine versus subaerial emplacement, and relative water depth (e.g., pillow basalt-volcaniclastic transition). © 2010 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Fedortchouk, Y.a , Matveev, S.b , Carlson, J.A.c 
H2O and CO2 in kimberlitic fluid as recorded by diamonds and olivines in several Ekati Diamond Mine kimberlites, Northwest Territories, Canada
(2010) Earth and Planetary Science Letters, 289 (3-4), pp. 549-559. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-73449108723&partnerID=40&md5=273452a86eeb002c518357cbca0d78e3
AFFILIATIONS: Department of Earth Sciences, Dalhousie University, Canada; 
Department of Earth and Atmospheric Sciences, University of Alberta, Canada; 
BHPBilliton Diamonds Inc., Kelowna, BC, Canada
ABSTRACT: Surface dissolution features on diamonds and Fourier Transform Infra Red spectroscopy (FTIR) of phenocrystal and xenocrystal olivines from kimberlites contain a record of magmatic fluid in kimberlite magmas. We investigated composition and behavior of kimberlitic fluid and the effect of volatiles on the eruption style and geology of kimberlites using microdiamonds and olivine concentrates from six kimberlite pipes with different lithologies and the character of diamond resorption (Ekati Diamond Mine, Northwest Territories, Canada). The study showed a clear correlation between the resorption style of diamond population of the kimberlites and the type of infrared (IR) spectra of their olivines. Four kimberlites have high quality diamonds with smooth regular surface features and high H2O content of the olivines indicating the presence of H2O-rich fluid during the emplacement. Fast ascent rates of fluid-rich magma can explain explosive eruption and filling the pipes with volcaniclastic kimberlite facies. Conversely, Grizzly and Leslie kimberlites have diamonds with complex sharp features diminishing diamond quality and indicating loss of the fluid. The slower ascent rates and less explosive eruption of the fluid-free magmas produced kimberlite pipes filled with magmatic facies kimberlite. Distinctive peaks in olivine IR spectra at 3356 and 3327 cm- 1 were found to correlate with the presence of hydrous magmatic fluid. Character of diamond morphology suggests that during the whole ascent of all six kimberlites, the magmatic fluid when present had a high H2O:CO2 ratio. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: diamond resorption;  FTIR spectroscopy;  kimberlitic fluid;  Lac de Gras kimberlites;  phenocrystal olivine
DOCUMENT TYPE: Article
SOURCE: Scopus

Costantini, L.a , Houghton, B.F.b , Bonadonna, C.a 
Constraints on eruption dynamics of basaltic explosive activity derived from chemical and microtextural study: The example of the Fontana Lapilli Plinian eruption, Nicaragua
(2010) Journal of Volcanology and Geothermal Research, 189 (3-4), pp. 207-224. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-73649090714&partnerID=40&md5=760b4702b2ee9a80d84d5d02a352166b
AFFILIATIONS: Département de Minéralogie, Section des Sciences de la Terre et de l'Environnement, Université de Genève., Rue des Maraichers 13, 1205 Genève, Switzerland; 
Department of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East-West Rd, Honolulu, HI 96822, United States
ABSTRACT: The Fontana Lapilli deposit is one of very few examples of basaltic Plinian eruptions discovered so far. Juvenile clasts have uniform chemical composition and moderate ranges of density and bulk vesicularity. However, clast populations include two textural varieties which are microlite-poor and microlite-rich respectively. These two clast types have the same clast density range, making a distinction impossible on that base alone. The high bubble number density (∼ 107 cm- 3) and small bubble population of the Fontana clasts suggest that the magma underwent coupled degassing following rapid decompression and fast ascent rate, leading to non-equilibrium degassing with continuous nucleation as it is common for silicic analogues. The Fontana products have lower microlite contents (10-60 vol.%) with respect to the other documented basaltic Plinian eruptions suggesting that the brittle fragmentation, implied for the other basaltic Plinian deposits, does not apply to the Fontana products and another fragmentation mechanism led the basaltic magma to erupt in a Plinian fashion. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: basaltic Plinian eruptions;  eruption dynamics;  Masaya volcano;  vesicle textures
DOCUMENT TYPE: Article
SOURCE: Scopus

Bonasia, R.a , Macedonio, G.a , Costa, A.a , Mele, D.b , Sulpizio, R.b 
Numerical inversion and analysis of tephra fallout deposits from the 472 AD sub-Plinian eruption at Vesuvius (Italy) through a new best-fit procedure
(2010) Journal of Volcanology and Geothermal Research, 189 (3-4), pp. 238-246. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-73649142716&partnerID=40&md5=f8a9716adadb06553a6e53a81ca0b377
AFFILIATIONS: Istituto Nazionale di Geofisica e Vulcanologia, Sezione Osservatorio Vesuviano, Napoli, Italy; 
CIRISIVU, Dipartimento Geomineralogico, Università degli Studi di Bari, Bari, Italy
ABSTRACT: A simple semi-analytical model for ash-fall deposit was applied to reconstruct the tephra deposits of the sub-Plinian 472 AD eruption of Vesuvius, Italy, which is of the scale of the reference eruptive scenario for the emergency planning, at Vesuvius. Applying a novel least-squares method, the bulk grain-size distribution, the total mass, and the eruption column height were obtained by fitting the computed ground load and granulometries with the observed ones. The analysis of the effect of three different weighting factors in the minimization procedure was also performed. Results showed that the statistical weighting factor produced the minimum bias. The best correlation between calculated and measured deposit was found, even though the quantity of the input data was not very high, as it commonly occurs for several ancient eruptions. Model results were also in agreement with estimations provided by other independent methods. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: HAZMAP model;  inverse problem;  Pollena eruption;  tephra fallout;  Vesuvius
DOCUMENT TYPE: Article
SOURCE: Scopus

Freundt, A.a  b , Hartmann, A.a , Kutterolf, S.a , Strauch, W.c 
Volcaniclastic stratigraphy of the Tiscapa maar crater walls (Managua, Nicaragua): Implications for volcanic and seismic hazards and Holocene climate changes
(2010) International Journal of Earth Sciences, 99 (6), pp. 1453-1470. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955771546&partnerID=40&md5=6301f9e2cd71d2226c473f1f82ef2cb2
AFFILIATIONS: SFB 574 at Kiel University, Wischhofstr. 1-3, 24148 Kiel, Germany; 
IFM-GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany; 
INETER, Managua, Nicaragua
ABSTRACT: The Tiscapa maar in the center of Managua city formed by a phreatomagmatic eruption &lt;3 ka ago. The eruption excavated a crater deep into the basement exposing a coherent Pleistocene to Holocene volcaniclastic succession that we have divided into four formations. The lowermost, &gt;60 ka old basaltic-andesitic formation F1 comprises mafic ignimbrites and phreatomagmatic tephras derived from the Las Sierras volcanic complex south of Managua. Formation F2 contains the ~60 ka basaltic-andesitic Fontana tephra erupted from the Las Nubes Caldera of the Las Sierras complex 15 km to the S, the 25 ka Upper Apoyo tephra from the Apoyo Caldera 35 km to the SE, and the Lower (~17 ka) and Upper (12. 4 ka) Apoyeque tephras from the Chiltepe volcanic complex 15 km to the NW. These tephras are separated by weathering horizons and paleosols indicating dry climatic conditions. Fluvial deposits of a SSW-NNE running paleo-river system build formation F3. The fluvial sediments contain, from bottom to top, scoriae from the ~6 ka basaltic San Antonio tephra, pumice lapilli from the Apoyo and Apoyeque tephras and the 6. 1 ka Xiloà tephra, and scoriae derived from the Fontana tephra. The fluvial sediment succession thus reflects progressively deeper carving erosion in the southern highlands (where a large-amplitude regional erosional unconformity exists at the appropriate stratigraphic level) that began after ~6 ka. This suggests that the mid-Holocene tropical high-precipitation climatic phase affected western Nicaragua about a thousand years later than other circum-Caribbean regions. The end of the wet climate phase ~3 ka ago is recorded by a deep weathering zone and paleosol atop formation F3 prior to the Tiscapa eruption. Formation F4 is the Tiscapa tuffring composed of pyroclastic surge and fallout deposits that cover a minimum area of 1. 2 km2. The 4 × 109 kg of erupted basaltic magma is compositionally and genetically related to the low-Ti basalts of the N-S striking Nejapa-Miraflores volcanic-tectonic alignment 5 km to the West of Tiscapa. Ascent and eruption mode of the Tiscapa magma were controlled by the Tiscapa fault that has a very active seismic history as it achieved 12 m displacement in about 3000 years. Managua city is thus exposed to continued seismic and volcanic risks. © 2009 Springer-Verlag.
AUTHOR KEYWORDS: Faulting and volcanism;  Fluvial sediments;  Maar eruption;  Paleoclimate;  Tephrostratigraphy
DOCUMENT TYPE: Article
SOURCE: Scopus

Hu, X.a , Jansa, L.b , Chen, L.a , Griffin, W.L.c , O'Reilly, S.Y.c , Wang, J.a 
Provenance of Lower Cretaceous Wölong Volcaniclastics in the Tibetan Tethyan Himalaya: Implications for the final breakup of Eastern Gondwana
(2010) Sedimentary Geology, 223 (3-4), pp. 193-205. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75549083302&partnerID=40&md5=7128839d3377299ba712dae07b054834
AFFILIATIONS: State Key Laboratory of Mineral Deposit Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China; 
Geological Survey of Canada-Atlantic, Dartmouth, N.S., Canada; 
GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, N.S.W. 2109, Australia
ABSTRACT: Lower Cretaceous volcanic lithic arenites, widely distributed in the Tethyan Himalaya, provide insights into the continental breakup of Eastern Gondwana. In southern Tibet they are represented by the Wölong Volcaniclastics. The volcanic rocks that contributed clastic material to the lower parts of this unit were predominantly alkali basalts, whereas rhyolitic/dacitic volcanism becomes the predominant source of the upper strata. Geochemical analyses of basaltic grains and of detrital Cr-spinels from the Wölong Volcaniclastics demonstrate the alkaline character of the volcanism and suggest "within-plate" tectonic setting for the volcanism. Zircon U-Pb ages confirm that this volcanism continued from ~ 140 Ma to ~ 119 Ma. Hf-isotope data on these Early Cretaceous zircons indicate that their parental magmas were mantle-derived, but in the later stage of magmatic activity mantle-derived magmas were mixed with partial melts derived from the continental crust.The Lower Cretaceous volcaniclastics occur along a broad belt paralleling the northern margin of Greater India. The onset of volcaniclastic deposition in the Himalayas appears to become progressively younger toward the west, but it ended synchronously during the Late Albian (~ 102 Ma). The low volume of volcanic rocks and their intra-plate tectonic setting suggest that they are the result of decompressional melting along extensional deep-seated fractures cross-cutting the continental crust, and reflect changes in regional intra-plate tectonic stresses when Greater India began to separate from the Australia-Antarctica supercontinent. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Detrital zircon;  Greater India;  Lower Cretaceous;  Provenance;  Southern Tibet;  Tethyan Himalaya;  U-Pb and Hf isotopes;  Wölong Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Testing plume and plate models of ocean plateau formation at Shatsky Rise, northwest Pacific Ocean
(2010) Integrated Ocean Drilling Program: Preliminary Reports, (324), pp. 1-115. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77649308515&partnerID=40&md5=5059a94e43f7103b7bb5080a91376504
ABSTRACT: Oceanic plateaus are giant volcanic features whose existence implies an extraordinary flux of magma from mantle to lithosphere. By understanding their formation, these large igneous provinces can be important indicators of fundamental processes of mantle convection and geodynamics. Although it is widely thought that oceanic plateaus arise from massive eruptions resulting from the arrival of a deep mantle plume head at the lithosphere, an alternative explanation is that plateau eruptions are related to decompression melting of unusually fusible mantle beneath fastspreading ridges. Shatsky Rise was cored during Expedition 324 because it is a unique oceanic plateau, formed during the Late Jurassic and Early Cretaceous at a rapidly spreading triple junction, with characteristics that could be attributed to either model of formation. Shatsky Rise is also a monster volcanic construct whose formation style is poorly understood. The goal of Expedition 324 was to core the igneous rocks of Shatsky Rise and the sediments above to examine the age, physical volcanology, geochemistry, and tectonic evolution of the rise as well as the sedimentation history. Five sites were cored and four were logged, with one site (U1346) on the summit of Shirshov Massif and two sites each on Ori (Sites U1349 and U1350) and Tamu (Sites U1347 and U1348) Massifs. Basaltic lava flows were recovered at four of these sites and complement previous Ocean Drilling Program Site 1213 (south flank of Tamu Massif) in providing a record of lava flow emplacement on Shatsky Rise. Instead of lava flows, cores from Site U1348 recovered a thick sequence (∼120 m) of volcaniclastic sediments topped with shallowwater carbonaceous sandstones. Lavas recovered at Sites U1347 and U1350 are fresh enough to be suitable for highquality radiometric age dating and planned geochemical/isotopic studies. Although lavas from Site U1346 and U1349 were moderately to highly altered, it is expected that they will provide important age information with suitable treatment and will be useful for most geochemical studies. Even though the volcaniclastic rocks of Site U1348 are highly altered, a single interval containing relatively fresh glass shards will provide valuable contestants on magma source characteristics. Shatsky Rise lava flows occur primarily as packages of pillow basalt and massive inflation units, frequently interbedded with volcaniclastic sediment. The richest massive inflation flows, up to ∼23 m thick, occur on Tamu Massif at Sites 1213 and U1347. They are similar to massive flows cored on Ontong Java Plateau and found in continental flood basalt provinces. At Site U1347, the relationship of pillows and massive flows suggests magmatic cycles that began with the emplacement of massive sheetflows and waned with pillow lavas. Moreover, paleomagnetic inclination trends at both Sites 1213 and U1347 imply that little time passed between the emplacement of individual flows. The implication is that Tamu Massif concluded with massive, high- effusion rate eruptions. Massive flows are also found at Sites U1349 and U1350, on Ori Massif's summit and flank, respectively, but the entire 53 m succession of igneous rocks cored at Site U1346, on the Shirshov Massif summit, consists of pillow lavas. The massive flow units are thinner at Ori Massif than most flows penetrated on Tamu Massif. Moreover, Site U1350 geochemical and paleomagnetic inclination trends imply greater time and more eruptive variability. The simplest conclusion from the observed trends in lava flow style across the three main edifices of Shatsky Rise is that the average eruptions become smaller and less effusive from Tamu to Ori to Shirshov massifs. Recovered basement rocks from the two summit sites (U1346 and U1349) on Shirshov and Ori massifs show the most severe alteration, apparently from both low and moderately higher temperature fluidrock interaction, the latter especially for Site U1349. In contrast, lavas cored on the deeper flanks of the massifs show evidence of only light to moderate lowtemperature alteration. Although these highly altered sites represent only two individual cases, this dichotomy suggests that alteration and fluidrock interaction was more intense on plateau summits. Apparently, the summits were a focus of heat and water circulation. Rocks at the flank sites (1213, U1347, and U1350) were apparently affected by lesser fluid flow and temperatures. Lavas at these sites seem to have been rapidly paved over by subsequent flows and thereby sealed from extensive seawater contact/circulation. Several sites attest that volcanic debris is more important on Shatsky Rise than anticipated. A significant portion (∼40 m) of the Site U1349 section, located on a summit ridge on Ori Massif, consists of volcaniclastic breccia. Site U1348, which is situated on a buried volcanic high on Tamu Massif, yielded a succession consisting entirely of volcaniclastic material, mainly hyaloclastic sediment. In addition, volcaniclastic sediments were found at Sites U1346 and U1347. These observations indicate that volcaniclastic eruptions made an important contribution to the formation of Shatsky Rise, especially on the higher, shallower parts of the volcanoes. Shipboard geochemical data show that the lava flows consist of variably evolved tholeiitic basalt. Site U1347 and U1350 lavas, least affected by alteration, have broad similarities with Site 1213 basalts and display compositional ranges overlapping those of Ontong Java Plateau basalts and midoceanridge basalt (MORB), although more with the latter. Samples from Site U1347 and many samples from Site U1350 resemble enrichedtype ocean ridge basalts. A broad generalization is that Shatsky Rise basalts are slightly enriched in incompatible elements compared to normal MORB (NMORB). This suggests a mantle source slightly richer in the more incompatible elements than NMORB source mantle and/or that Shatsky Rise magmas formed by slightly lower degrees of partial melting and possibly in the presence of residual garnet. Alterationresistant element ratios indicate that basalts from Sites U1346, U1348, and U1349 are also tholeiites. Site U1349 basaltic flows appear to represent significantly less differentiated magmas than those recovered from other sites and have similarities to picritic Ontong Java Plateau basalts (i.e., the highMg Kroenke type). Multiple lines of evidence indicate that Shatsky Rise volcanoes had summits at or above sea level. Benthic foraminifers and/or sediment facies at all sites except Site U1350 (a lower flank site) show evidence of shallowwater deposition. Lavas at Site U1349 have alteration and flow structures consistent with subaerial eruption and weathering as well as intercalations of shallowwater sediments (e.g., oolites). Most of the volcaniclastic deposition at Site U1348 occurred below sea level, but the succession was topped with shallowwater sediment. Two of the sites showing evidence of shallowwater deposition (Sites U1347 and U1348) are significantly downslope from today's highest points of basement level on Tamu Massif, implying that the summit was a large, emergent island. All together, evidence from Expedition 324 strongly implies that during Jurassic and Cretaceous times, Shatsky Rise was an archipelago of large volcanic islands.
DOCUMENT TYPE: Article
SOURCE: Scopus

Browne, B.a , Izbekov, P.b , Eichelberger, J.c , Churikova, T.d 
Pre-eruptive storage conditions of the Holocene dacite erupted from Kizimen Volcano, Kamchatka
(2010) International Geology Review, 52 (1), pp. 95-110. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-75449110729&partnerID=40&md5=f85f46462cff3b379027c47a070d27ae
AFFILIATIONS: Department of Geological Sciences, California State University, Fullerton, CA, United States; 
Geophysical Institute - Alaska Volcano Observatory, University of Alaska Fairbanks, Fairbanks, AK, United States; 
US Geological Survey Volcano Hazards Program USGS HQ - GD, Reston, VA, United States; 
Institute of Volcanology and Seismology, Far East Division, Russian Academy of Sciences, Petropavlovsk-Kamchatsky, Russian Federation
ABSTRACT: This study describes an investigation of the pre-eruptive conditions (T, P and fO2) of dacite magma erupted during the KZI cycle (12,000-8400 years ago) of Kizimen Volcano, Kamchatka, the earliest, most voluminous and most explosive eruption cycle in the Kizimen record. Hydrothermal, water-saturated experiments on KZI dacite pumice coupled with titanomagnetite-ilmenite geothermometry calculations require that the KZI dacite existed at a temperature of 823 ± 20°C and pressures of 125-150 MPa immediately prior to eruption. This estimate corresponds to a lithologic contact between Miocene volcaniclastic rocks and Pliocene-Pleistocene volcanic rocks located at a depth of 5-6 km beneath the Kizimen edifice, which may have facilitated the accumulation of atypically large volumes of gas-rich dacite during the KZI cycle.
AUTHOR KEYWORDS: Experimental petrology;  Kamchatka;  Kizimen volcano;  Magma accumulation;  Magma storage
DOCUMENT TYPE: Article
SOURCE: Scopus

Zanoni, D.a  b , Spalla, M.I.a  c , Gosso, G.a  c 
Vestiges of lost tectonic units in conglomerate pebbles? a test in permian sequences of the Southalpine Orobic Alps
(2010) Geological Magazine, 147 (1), pp. 98-122. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77953621840&partnerID=40&md5=7f3a299807b6508bee98197793b65a1c
AFFILIATIONS: Dipartimento di Scienze della Terra 'A. Desio', Università Degli Studi di Milano, Via Mangiagalli 34, 20133 Milano, Italy; 
Department of Geology, University of New Brunswick, 2 Bailey Drive, Fredericton, NB E3B 5A3, Canada; 
C.N.R.-I.D.P.A., Via Mangiagalli 34, 20133 Milano, Italy
ABSTRACT: Microstructural analysis and P-T estimates of metamorphic pebbles in Permian conglomerates of the Central Southern Alps, representing the erosion product of the collapsing Variscan chain, are the discriminating tools for determining the metamorphic sequences representing potential sources of the conglomerates. In the selected case, basement units are precisely outlined on the basis of quality P-T-d-t paths that allow reconstruction of their metamorphic evolutions (tectonometamorphic units); this facilitates individuation of the basement sources with much better confidence. The lower Permian volcaniclastic sequence of the Eastern Orobic Basin, which overlies the Variscan Val Vedello basement, comprises the Aga and Vedello conglomerates, which are the oldest deposits containing a considerable amount of up to metre-sized metamorphic pebbles. Microstructural and mineral chemical data on metamorphic pebbles of the Aga and Vedello conglomerates were used to infer quantitative pre-Permian P-T evolutions, which are compared with those of the tectonometamorphic units constituting the surrounding Southalpine metamorphic basement. Two types of P-T evolution are recorded in the metamorphic pebbles of Aga and Vedello conglomerates: Type 1 is characterized by an amphibolite-facies imprint, followed by greenschist retrogression; Type 2 is characterized by three successive greenschist-facies re-equilibrations. The Type 1 P-T evolution of metamorphic pebbles matches with that of the adjacent tectonometamorphic unit of the Val Vedello basement. Type 2 is similar to those recorded in units B and C of the North East Orobic basement, and it differs from that of the adjacent Val Vedello basement. This suggests that the Aga and Vedello conglomerates were fed by two different basement sources: one consisting of the present day Val Vedello basement, and the other compatible with units B and C of the North East Orobic basement. According to the P/T ratios of the Tmax-PTmax imprints, both basement sources recorded the Variscan collision but at a different crustal level. The age (c. 278 Ma) of the Aga and Vedello conglomerates constrains the minimum exhumation age for their basement sources. Copyright © Cambridge University Press 2009.
AUTHOR KEYWORDS: Lower Permian conglomerates;  Pebble P-T paths;  Southern Alps;  Variscan tectonometamorphic units
DOCUMENT TYPE: Article
SOURCE: Scopus

Zimmermann, U.a  d , Niemeyer, H.b , Meffre, S.c 
Revealing the continental margin of Gondwana: The Ordovician arc of the Cordón de Lila (northern Chile)
(2010) International Journal of Earth Sciences, 99 (SUPPL. 1), pp. 39-56. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956271191&partnerID=40&md5=a6633d02e0f74f77b1c7d1b644fa7ce1
AFFILIATIONS: Department of Petroleum Engineering, University of Stavanger, 4036 Stavanger, Norway; 
Department of Geology, University of Johannesburg, Johannesburg, South Africa; 
Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile; 
ARC Centre of Excellence in Ore Deposits, School of Earth Sciences, University of Tasmania, Hobart, Australia
ABSTRACT: The tectonic evolution of the proto-Andean margin of western Gondwana has been commonly seen in terms of terrane accretion processes, requiring the existence of early Palaeozoic terrane boundaries and associated sutures. A new study of the Cordón de Lila Ordovician volcano-sedimentary successions in northern Chile reveals for the first time an arc assemblage deposited on thin crust within a continental arc system, having regional implications. Primitive basalts, rhyolites, volcanogenic wackes and siltstones are associated, bearing not only debris from mainly arc sources but also basement rocks; the latter is only accessory in the form of metamorphic lithoclasts and detrital zircons with ages around 1.0 Ga. Magmatic zircons in rhyolites reveal an eruptive age of ca. 478 Ma, concordant with Upper Arenigian to Lower Llanvirnian ages of brachiopods in overlying conglomerates. Bimodal volcanic associations, including low-K tholeiites, characterize the magmatic rocks, with evolved rhyolitic rocks showing pronounced arc-like geochemical signatures (negative anomalies in Ti, Nb and Ta). Some of the basaltic rocks are tholeiitic and display Ce/Y ratios below 1 and might point to a Moho depth of less than 10 km, hence a thin continental crust, coinciding with depletions in Zr and Hf concentrations. Associated volcaniclastic rocks display generally low Th/Sc (0.4-1), La/Sc (mostly >3.5), Zr/Sc (6-20) and high Ti/Zr (~10-60) ratios. The rock succession resembles the same geochemical and lithostratigraphical trends as retro-arc basin deposits further east in the Argentinean Puna of similar age. However, in the Cordón de Lila, the intercalated mafic rocks are less evolved, and the percentage of arc debris is higher, while the percentage of metamorphic lithoclasts and rounded quartz grains is much lower, indicating the existence of a thinned continental margin underpinning. We propose a transition in the Ordovician of the Central Andes from trench-ward fore-arc deposits to a dominantly intra-arc basin (Cordón de Lila), transitioning further eastwards towards a retro-arc basin (Puna) and foreland basin deposits of the Cordillera Oriental of northwestern Argentina. The Cordón de Lila intra-arc assemblage and associated fore-arc basin deposits therefore defined the western margin of Gondwana during the Ordovician. The absence of any terrane boundaries and sutures across strike is consistent with an evolving continental margin arc constructed on attenuated crust of the proto-Andean margin. © 2009 Springer-Verlag.
AUTHOR KEYWORDS: Active continental margin;  Basin evolution;  Cordón de Lila (Chile);  Lower Ordovician;  Provenance;  U-Pb age dating;  Western margin of Gondwana
DOCUMENT TYPE: Article
SOURCE: Scopus

O'Reilly, B.M.a , Hauser, F.a  b , Readman, P.W.a 
The fine-scale structure of upper continental lithosphere from seismic waveform methods: Insights into Phanerozoic crustal formation processes
(2010) Geophysical Journal International, 180 (1), pp. 101-124. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-73049089724&partnerID=40&md5=42643339978f14fd036566b0dada3e54
AFFILIATIONS: Geophysics Section, Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland; 
UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland
ABSTRACT: Studies of the fine-scale structure of the continental lithosphere using seismic coda, associated with reflections from within the crust and the uppermost mantle, have almost solely been based on the compressional wavefield, observed at near vertical to wide-angle incidence. Here the results from a full waveform analysis of both P- and S-wave coda, obtained during a crustal scale wide-angle refraction experiment, from southwest Ireland are presented. The basic foundation for the study is a 2-D model for the P- and S-wave structure of the crust and its chemical composition, based on traveltime inversion of first arrivals and reflections for the Irish Caledonides. This sector of the Caledonian orogenic belt straddles the boundary between the Laurentian and Avalonian tectonic plates, along the Iapetus Suture Zone. The excellent quality and relatively broad frequency range (e.g. 1-20 Hz) of the P- and S-wave coda permits finer structure in the upper 40 km of lithosphere to be resolved than would be possible using just primary seismic phases. A series of 1-D waveform calculations are performed to systematically build a model for the fine-scale structure of the 32-km-thick crust and the uppermost mantle lithosphere. Petrophysical and geochemical data from felsic lower-crustal xenoliths from Central Ireland place limits on the permitted velocity fluctuations. Additional constraints are imposed by vertical P-wave reflections observed on contiguous offshore seismic reflection profiles. The results indicate that the uppermost mantle to a depth of ca. 40 km consists of a vertically stacked sequence of alternating high (Vp ∼ 8.0 km s-1) and low (Vp ∼ 7.25 km s-1) velocity layers. Each layer is about 500 m thick with a Vp/. Vs ratio ∼1.73. These layers are interpreted as a series of lens-shaped mafic sill complexes, intruded into the subcrustal lithosphere. The fine structure within the lower crust consists of similar seismic velocity fluctuations (Vp ∼ 6.4 and 7.1 km s-1) but on a scale of 200-300 m thickness. Velocity variations within the lower crust are consistent with the petrophysical properties of metapelitic, orthogneissic and psammitic lithologies, from lower-crustal xenoliths in Central Ireland, and with similar exhumed sections of lower crust in southern Europe. These results support tectonic theories for the origin of the crust by tectonic accretion of predominantly sedimentary and volcaniclastic material derived from oceanic, island-arc and continental margin sources during the Caledonian orogenic cycle. A conceptual model for crustal accretion and growth involves partial melting of the accreted sedimentary wedge, producing granites and a chemically differentiated crust during the late Caledonian (latest Silurian/early Devonian). The heat source that drove melting of the accreted sediments may have been provided by the interpreted mafic sills intruded into the uppermost mantle during oblique late Caledonian (sinistral) collision of the Laurentian and Avalonian plates. © 2009 The Authors Journal compilation © 2009 RAS.
AUTHOR KEYWORDS: Continental margins: convergent;  Controlled source seismology;  Crustal structure;  Europe
DOCUMENT TYPE: Article
SOURCE: Scopus

Yan, Q., Shi, X.
Characteristics of volcaniclastic rocks from seamounts in the South China Sea and its geological implications
(2009) Acta Petrologica Sinica, 25 (12), pp. 3327-3334 begin_of_the_skype_highlighting              3327-3334      end_of_the_skype_highlighting. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77949666373&partnerID=40&md5=0f71adb708d85b2b7aa84c920319f9ad
AFFILIATIONS: Key Lab of Marine Sedimentary and Environmental Geology, State Oceanic Administration, Qingdao 266061, China
ABSTRACT: Volcaniclastic rock on seamount is the product of subaqueous explosive volcanism. The finding of volcaniclastic rocks from, two seamounts in the South China Sea suggests that the top of seamounts once exceeded the pressure compensation level. ( PCL ). Petrographie characteristics display that the cementing material mainly is a mixed phase including clay minerals and Fe-oxides, which, to one's extent, reflects that it is difficult for coarse-size epiclastic debris to reach the top of seamount due to the obstruction of positive relief of seamount. The characteristics of mineral compositions and major element of volcaniclastic rocks are comparable to those of alkali, basaltic rocks from the same seamount, and these volcaniclastic rocks also belongs to alkali magma series based, on mineralogy and major element data. The calculated minimal and maximal subsidence rates for seamounts in the South China Sea are 0. 06mm/year and 0. 30mm/year, respectively. Physical, weathering products of rocks from seamounts have a significant contributor to the adjacent basin.
AUTHOR KEYWORDS: Seamount;  South China Sea;  Subsidence rate;  Tectonic setting;  Volcaniclastic rock
DOCUMENT TYPE: Article
SOURCE: Scopus

Perriello Zampelli, S.
Evaluation of sliding susceptibility in volcaniclastic soils of campania (southern Italy) aided by gis techniques
(2009) Geografia Fisica e Dinamica Quaternaria, 32 (2), pp. 227-236. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-75449085946&partnerID=40&md5=cac4d1350a974824d8c12e58f2f9b795
AFFILIATIONS: Dipartimento di Scienze della Terra, Università di Napoli Federico II, Largo S. Marcellino 10, 80138 Napoli
ABSTRACT: A method for evaluating the susceptibility to debris slides, due to critical rainfall sequences, is discussed. The method concerns the volcaniclastic soils of Campania (Southern Italy) covering carbonatic slopes. It is based on the concept that, for a spatially homogeneous soil cover and a spatially homogeneous triggering rainfall sequence, different values of threshold slope gradient exist for limit equilibrium conditions, depending on the continuity and planform curvature of the soil cover. The method derives from the analysis of the location of the source areas of the landslides originated on May 5, 1998, on the slopes of the Pizzo d'Alvano massif, when more than a hundred of almost contemporary debris slides were triggered, providing a consistent data set. In order to test the potential of the method for the spatial prediction of debris slide triggering also in other areas of Campania displaying similar geomorphology and soil cover, it has first been applied to that same massif to verify, although a posteriori, its ability to assess the sliding susceptibility of the volcaniclastic soils prior to the May 1998 event. Comparison of the sliding susceptibility resulting from the method and the locations of the actual May 5, 1998, landslide source areas provided good results: the susceptible areas, covering 15 % of the studied area, overestimated the actual source areas, while 94 % of the actual source areas fell into susceptible areas. Accordingly, a simplified version of the method has been applied to a much larger area, historically and also recently struck by debris slides - debris avalanches - debris flows. Although, in this latter case, a comparison of the resulting sliding susceptibility with the locations of actual landslide source areas could be carried out only for a limited number of recent events, the results have provided useful hints for analysing the risk associated to this type of landslides in Campania. While it has originally been developed with regard to the volcaniclastic soil covers of Campania, where the role of discontinuities is generally deemed as particularly relevant to the spatial distribution of the source areas of debris slides, the method discussed in the present paper could profitably be used (with suitable adaptation and calibration) for assessing the rainfall-triggered shallow landsliding susceptibility also in different, residual and/or colluvial soil, contexts.
AUTHOR KEYWORDS: Campania (Italy);  Debris-slide susceptibility;  Ground curvature;  Soil cover discontinuities;  Volcaniclastic soil cover
DOCUMENT TYPE: Article
SOURCE: Scopus

Milia, A.a , Raspini, A.b , Torrente, M.M.c 
Evidence of slope instabilities and tsunami associated with the 3.5 ka Avellino eruption of Somma-Vesuvius volcano, Italy
(2009) Geological Society Special Publication, (322), pp. 105-119. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-74949101061&partnerID=40&md5=8c3488a915bf3b2a9011878df923c6e6
AFFILIATIONS: Istituto per l'Ambiente Marino Costiero (IAMC), CNR, Calata Porta di Massa, Porto di Napoli, 80133, Napoli, Italy; 
Istituto di Geoscienze e Georisorse (IGG), CNR, Via Giorgio La Pira, 4, 50121, Firenze, Italy; 
Dipartimento di Studi Geologici ed Ambientali (DSGA), Università del Sannio, Via Portarsa 11, 82100, Benevento, Italy
ABSTRACT: The interpretation of high-resolution seismic profiles acquired close the eastern coast of the Bay of Naples offshore Somma-Vesuvius volcano, and calibrated by borehole data, allowed us to recognize a reflection-free seismic facies consisting of a volcaniclastic debris avalanche overlain by pyroclastic density current deposits. Both are associated with the 3.5 ka 'Avellino eruption' and are in turn overlain by a marine succession. The top of the volcaniclastic unit corresponds to a deep erosional surface covered by a coarse-grained bioclastic layer with rounded pumice. We argue that these features are related to a tsunami that was triggered by the sudden entrance into the sea of the gigantic (&gt;1km3) volcaniclastic unit. The onshore-offshore correlation and mapping of this volcaniclastic unit have allowed us to evaluate its distribution west of Somma-Vesuvius. The pyroclastic density current deposits terminate seaward at 40 m water depth; at the same depth the debris avalanche is affected by a gravitational instability. Over the last 3.5 ka the slump has been in constant movement, as documented by the angular unconformities at the top of the chaotic seismic unit and within the overlying marine deposits. © The Geological Society of London 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Oyhantçabal, P.a , Siegesmund, S.b , Wemmer, K.b , Presnyakov, S.c , Layer, P.d 
Geochronological constraints on the evolution of the southern Dom Feliciano Belt (Uruguay)
(2009) Journal of the Geological Society, 166 (6), pp. 1075-1084. Cited 19 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350584481&partnerID=40&md5=9b8ba2f5b9ce8eed17f364bb5787ccb9
AFFILIATIONS: Departamento de Geología, Facultad de Ciencias, Universidad de la República, Iguá 4225, C.P. 11400, Montevideo, Uruguay; 
Geoscience Centre of the Georg-August University Gottingen, Goldschmidtstr. 3, 37077 Gottingen, Germany; 
Centre of Isotopic Research, Karpinsky Geological Institute (VSEGEI), Sredny Prospect 74, St. Petersburg 199106, Russian Federation; 
Geophysical Institute, University of Alaska, Fairbanks, AK 99775, United States
ABSTRACT: New U-Pb sensitive high-resolution ion microprobe, K-Ar and Ar-Ar data from the southernmost Dom Feliciano Belt allow the identification of four major events. Orthogneisses from the Punta del Este Terrane indicate a magmatic episode at c. 770 Ma and high-grade metamorphism at 641 17 Ma. Granitoid emplacement at 627 23 Ma was roughly coeval with peak metamorphism. Volcaniclastic rocks of the Las Ventanas Formation dated at 573 11 Ma can be correlated with the peripheral foreland basin (571 8 Ma). Transpression and coeval high-K calc-alkaline magmatism is recorded in the Maldonado granite dated at 564 7 Ma. The following events are postulated: (1) magmatism at 850-750 Ma related to rifting; (2) metamorphism and granite emplacement at 650-600 Ma; (3) molasse sequences and foreland basins at c. 573 Ma; (4) late magmatism at 580-560 Ma associated with transpression. The data indicate that (1) the Punta del Este Terrane could be a portion of the Coastal Terrane of the Kaoko Belt, (2) granitoid emplacement at 650-600 Ma in the Punta del Este and Nico Pérez terranes favours westward subduction, and (3) widespread post-collisional synkinematic magmatism occurred in the Dom Feliciano and Kaoko belts between 580 and 550 Ma. © 2009 Geological Society of London.
DOCUMENT TYPE: Article
SOURCE: Scopus

Farris, D.W.
Construction and evolution of the Kodiak Talkeetna arc crustal section, southern Alaska
(2009) Special Paper of the Geological Society of America, (456), pp. 69-96. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-74949133251&partnerID=40&md5=1bec2f382b4c08d44d972dabd0c13451
AFFILIATIONS: Department of Geological Sciences, Florida State University, Tallahassee, FA 32306, United States
ABSTRACT: The Kodiak Border Ranges ultramafi c complex, Afognak batholith, and Shuyak Formation on Kodiak and Afognak Islands together form the lower, middle, and upper portions, respectively, of a Jurassic-Triassic island-arc crustal section. The Kodiak section exhibits structural and geochemical trends similar, but not identical to, the Tonsina-Nelchina segment of the Talkeetna arc, located >500 km to the northeast. Exposed at the base of the Kodiak section is cumulate clinopyroxenite with associated dunite, wehrlite, and layered gabbro. In the inferred middle to upper crust, tonalite and quartz diorite of the Afognak batholith intrude Shuyak Formation basaltic fl ows, basaltic pillow lavas, and volcaniclastic sedimentary rocks. Despite the fault-bounded nature of the lower crustal and mantle rocks, continuous chemical trends in elements such as MgO, Ni, Cr, Nb, Sr, Y, and rare-earth elements exist across all three units. Modeling of these data suggest that Kodiak arc evolution occurred in two main stages: (1) a gabbroic initial melt underwent fractional crystallization that produced a pyroxenitic root and a gabbroic lower crust, and (2) melt in equilibrium with the gabbroic lower crust underwent assimilation-fractional crystallization to produce mid-crustal plutonic and upper-crustal volcanic rocks. Kodiak Island exposes the oldest and thinnest portion of the Talkeetna arc, with ages from the Afognak batholith ranging from ca. 215-185 Ma. In the eastern and western Talkeetna arc, magmatism migrated northward after ca. 180 Ma in response to inferred forearc erosion. Forearc erosion coupled with differential subductionchannel movement juxtaposed blueschist-facies rocks with middle and lower crustal arc rocks. These processes occurred earlier and to a greater degree in the western Talkeetna arc, causing the arc to split in half, separating the Kodiak and Alaskan Peninsula parts of the Talkeetna arc. © 2009 The Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Zhai, W.a  b , Sun, X.a  b , Sun, W.c  d , Su, L.b , He, X.e , Wu, Y.e 
Geology, geochemistry, and genesis of Axi: A Paleozoic low-sulfidation type epithermal gold deposit in Xinjiang, China
(2009) Ore Geology Reviews, 36 (4), pp. 265-281. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349972519&partnerID=40&md5=8f8dd134d75428155c312e4e87078f33
AFFILIATIONS: School of Marine Sciences, Sun Yat-Sen University, Guangzhou, 510275, China; 
Department of Earth Sciences, Sun Yat-Sen University, Guangzhou, 510275, China; 
Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China; 
School of Earth and Space Sciences, University of Science and Technology of China, Heifei, 230026, China; 
Axi Gold Mine, Yining, Xinjiang 835000, China
ABSTRACT: Axi is a low-sulfidation type epithermal gold deposit hosted in Paleozoic subaerial volcanic rocks in the western Tianshan orogenic belt, Xinjiang, China. The resource is more than 50 t gold at an average grade of &gt; 4.4 ppm. The deposit occurs in the Tulasu volcanic fault-basin in the Paleozoic active continental margin on the northern side of the Yili-Central Tianshan plate. The host rocks are andesitic volcaniclastic rocks of the Paleozoic Dahalajunshan Formation, and the orebodies occur as veins in annular faults of a paleocaldera. Mineralization at Axi can be subdivided into five stages: quartz and/or chalcedony vein, quartz vein, quartz-carbonate vein, sulfide vein and carbonate vein. There are two types of ore host: quartz vein and altered rocks. Ore minerals are native gold, electrum, pyrite, marcasite, arsenopyrite, hematite, limonite, and trace amounts of pyrargyrite, polybasite, naumannite, cerargyrite, sphalerite, chalcopyrite, tetrahedrite, galena, pyrrhotite and clausthalite; gangue minerals are mainly quartz, chalcedony, illite, calcite, siderite, dolomite, adularia and laumontite. The main wall-rock alteration is silicification and phyllic alteration, carbonatization and propylitization. The deposit is characterized by an enrichment, relative to crustal abundance, of Au, Ag, As, Sb, Bi, Hg, Se, Te and Mo, depletion in base metals (Cu, Pb, and Zn), and a low Ag/Au ratio (0.5-3.7). Three types of fluid inclusions were recognized in quartz from the major mineralization stages: liquid aqueous inclusions, liquid-rich two-phase inclusions and small amounts of vapor-rich two-phase inclusions. Microthermometric measurements indicate that the final ice melting temperatures are - 0.3 to - 4.4 °C, corresponding to salinities of 0.5-6.9 wt.% NaCl equiv. (2.2 wt.% NaCl equiv. in average). The peak temperatures of ice melting varies from - 0.4 to - 1.9 °C, corresponding to salinities of 0.7-3.1 wt.% NaCl equiv. Homogenization temperatures range mainly between 120 and 240 °C, with an average of 190 °C and a maximum of 335 °C. The fluid density is 0.73 to 0.95 g/cm3 and thus the estimated maximum mineralization depth is about 700 m. Hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range: δDH2O is - 98 to - 116‰ and δ18OH2O - 1.8 to 0.4‰. 3He/4He ranges from 0.0218 to 0.138 Ra, with an average of 0.044 Ra, indicating that He derived predominantly from crust with negligible mantle He in the ore fluids. By contrast, the 40Ar/36Ar ranges from 317.7 to 866.0, suggesting that crust-derived radioactive 40Ar* accounts for 7.0 to 66%, and atmospheric 40Ar about 43 to 93% in the ore fluids. Hydrogen, oxygen, carbon, sulfur and noble gas isotopes indicate that the ore-forming fluids of the Axi gold deposit consisted predominantly of circulating meteoric water. Ore-forming metals may have derived mainly from the host volcaniclastic rocks of the Dahalajunshan Formation and basement rocks. The occurrence of adularia, platy calcite, and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins, and occurrence of aqueous liquid, and liquid-rich and vapor-rich two-phase inclusions, indicates that boiling of the ore-forming fluid have occurred, leading to supersaturation of the hydrothermal solution and deposition of ore metals. This is the main mineralization mechanism for quartz-vein type ores in Axi. The ore-forming fluid was buffered to a near-neutral pH in a reduced environment during mineralization. The preservation of this Paleozoic Axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit, and minimal amount of erosion after Late Cenozoic uplift. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Axi;  Boiling;  Fluid inclusions;  Isotope;  Paleozoic low-sulfidation type epithermal gold deposit;  Tianshan orogenic belt
DOCUMENT TYPE: Article
SOURCE: Scopus

Ramirez, L.E.a , Rae, A.J.a , Bardsley, C.b , Bignall, G.a 
Spatial variation of high temperature hydrothermal activity at Mokai geothermal field, Taupo Volcanic Zone, New Zealand
(2009) Transactions - Geothermal Resources Council, 33, pp. 753-755. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77952633580&partnerID=40&md5=4ef8d0fe410047ef54614ec53ed160a0
AFFILIATIONS: Wairakei Research Centre, GNS Science, Taupo, New Zealand; 
Mighty River Power Limited, Hamilton, New Zealand
ABSTRACT: The Mokai geothermal system is located 25 km north-west of the Wairakei field in the western part of the Taupo Volcanic Zone, North Island, New Zealand. Its deep production reservoir is defined by a microgravity anomaly of about 4-5 km2 extent, with north and north-easterly lateral outflows toward the Waikato River. The Mokai stratigraphy is dominated by a sequence of variably welded ignimbrites, rhyolite lavas and breccias, pumiceous fall deposits and volcaniclastic sediments (inferred basement Torlesse greywacke has not been encountered by drilling), cross-cut by NE-trending normal faults. Production wells are located above the deep production reservoir, where encountered temperatures are largely greater than 240°C, but also above 300°C. Injection wells are located in N, NW and NNE sectors of the field. Petrographic examination of core and drill cuttings, combined with fluid inclusion microthermometry and qualitative clay fraction XRD analyses of three injection wells, provide mineralogical and textural evidence for the coexistence of a "high" temperature hydro-thermal mineral assemblage (e.g.,actinolite,epidote; &gt;300°C) with a "low" temperature mineral assemblage (e.g., smectite, laumon- tite; &lt;220°C) at the same depths. The inference is that the outflow region of the Mokai reservoir is now cooler than at some time in the past and that this temperature change has occurred without any substantial change in fluid chemistry. It is likely to have been caused either by thermal contraction of a slowly cooling geothermal reservoir, or by a heat source that has migrated towards the S and SE to where the present geothermal upflow is situated.
AUTHOR KEYWORDS: Mokai geothermal field;  New zealand;  Taupo Volcanic Zone
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

Kralj, P.a , Rychagov, S.b , Kralj, P.c 
Zeolites in volcanic-igneous hydrothermal systems: A case study of Pauzhetka geothermal field (Kamchatka) and Oligocene Smrekovec volcanic complex (Slovenia)
(2009) Environmental Earth Sciences, 59 (5), pp. 951-956. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955149615&partnerID=40&md5=9827d55e8272b2a503dfc3dc1ec64192
AFFILIATIONS: Geological Survey of Slovenia, Dimiceva 14, 1000 Ljubljana, Slovenia; 
Institute of Volcanology and Seismology, Piip Blv 9, 63008 Petropavlovsk-Kamchatsky, Russian Federation; 
Gejzir Consulting, Turnerjeva 17, 1000 Ljubljana, Slovenia
ABSTRACT: Production from geothermal reservoirs in volcanic-igneous hydrothermal systems may be disturbed owing to the formation of authigenic minerals that reduce primary porosity and infill fissure systems. Crystallization may be induced by natural processes or human activity related to the reservoir exploitation. In volcanic and volcaniclastic rocks, zeolites and related authigenic silicate minerals commonly develop. Two selected study sites-Pauzhetka geothermal field in Russia and Smrekovec volcanic complex in Slovenia are characterized by extensive development of progressive stage medium-and low-temperature propylitization and zeolitization with similar mineral assemblages that reduced original reservoir rock porosity and permeability. Retrograde and overprinting reactions of argillitization commonly enhance porosity and permeability of rocks, but some other reactions, like from prehnite to laumontite, from laumontite to heulandite, and from laumontite to analcime, encountered in the Smrekovec volcanic complex reduced it appreciably. Retrograde reactions recognized in the study sites were not induced by the temperature drop only, but were accompanied by the change in chemical composition of reacting fluids. Chemical composition of interstitial waters produced from exploitation wells in the Pauzhetka geothermal field indicate that propylitic and zeolite facies alteration is related to Na-Cl, slightly alkaline waters, while argillitization involved acidic thermal waters with more complex ion composition. © Springer-Verlag 2009.
AUTHOR KEYWORDS: Hydrothermal alteration;  Pauzhetka-kamchatka;  Propylites;  Slovenia;  Thermal waters;  Volcanic-igneous systems;  Zeolites
DOCUMENT TYPE: Article
SOURCE: Scopus

White, J.D.L.a , Bryan, S.E.b  c , Ross, P.-S.a  d , Self, S.e , Thordarson, T.f 
Physical volcanology of continental large igneous provinces: Update and review
(2009) Special Publications of IAVCEI, (2), pp. 291-321. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77956649216&partnerID=40&md5=5f10781e0d1951f83ffaff5ec65ac80d
AFFILIATIONS: Department of Geology, University of Otago, PO Box 56, Dunedin, New Zealand; 
Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, United States; 
Centre for Earth and Environmental Science Research, School of Earth Sciences and Geography, Kingston University, Penrhyn Road, Kingston upon Thames, Surrey KT1 2EE, United Kingdom; 
INRS-ETE, 490 rue de la Couronne, Québec, G1K 9A9, Canada; 
Open University, Department of Earth Sciences, Milton Keynes MK7 6AA, United Kingdom; 
School of Earth Science, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 3JW, United Kingdom
ABSTRACT: Large igneous provinces (LIPs) form in both oceanic and continental settings by the emplacement and eruption of voluminous magmas ranging from basalt to rhyolite in composition. Continental flood basalt provinces are the best studied LIPs and consist of crustal intrusive systems, extensive flood lavas and ignimbrites, and mafic volcaniclastic deposits in varying proportions. Intrusive rocks are inferred to represent the solidified remnants of a plumbing system that fed eruptions at the surface, as well as themselves representing substantial accumulations of magma in the subsurface. The vast majority of intrusive rock within the upper crust is in widespread sills, the emplacement of which may structurally isolate and dismember upper crustal strata from underlying basement, as well as spawning dyke assemblages of complex geometry. Interaction of dykes and shoaling sills with near-surface aquifers is implicated in development of mafic volcaniclastic deposits which, in better-studied provinces, comprise large vent complexes and substantial primary volcaniclastic deposits. Flood lavas generally postdate and overlie mafic volcaniclastic deposits, and are emplaced as pahoehoe flows at a grand scale (up to 10 4 km2) from eruptions lasting years to decades. As with modern Hawaiian analogues, pahoehoe flood lavas have erupted from fissure vents that sometimes show evidence of high lava fountains at times during eruption. In contrast to basaltic provinces, in which volcaniclastic deposits are significant but not dominant, silicic LIPs are dominated by deposits of explosive volcanism, although they also contain variably significant contributions from widespread lavas. Few vent sites have been identified for silicic eruptive units in LIPs, but it has been recognized that some ignimbrites have also been erupted from fissure-like vents. Although silicic LIPs are an important, albeit less common, expression of LIP events along continental margins, the large volumes of easily erodible primary volcaniclastic deposits result in these provinces also having a significant sedimentary signature in the geologic record. The inter-relationships between flood basalt lavas and volcaniclastic deposits during LIP formation can provide important constraints on the relative timings between LIP magmatism, extension, kilometre-scale uplift and palaeoenvironmental changes. © IAVCEI 2009.
DOCUMENT TYPE: Review
SOURCE: Scopus

Wastegård, S.a , Andersson, S.a , Perkins, V.H.b 
A new mid-holocene tephra in central Sweden
(2009) GFF, 131 (4), pp. 293-297. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-72149112196&partnerID=40&md5=7bc2ba65df2a9892d2774a1897b37ff5
AFFILIATIONS: Department of Physical Geography and Quaternary Geology, Stockholm University, SE-106 91 Stockholm, Sweden; 
Christ's College, St Andrews Street, Cambridge, CB2 3BU, United Kingdom
ABSTRACT: A mid-Holocene tephra, LBA-2 has been found in a peat bog in central Sweden. Geochemical analyses suggest an origin in an evolved volcanic centre, most likely the Snæfellsnes volcanic centre in western Iceland. The geochemistry of the LBA-2 tephra is similar to the youngest of three silicic tephra layers from Snæfellsjökull, Sn-1 dated to 1780 cal yr BP. However, wiggle-match dating indicates an age of 3550-3650 begin_of_the_skype_highlighting              3550-3650      end_of_the_skype_highlighting cal yr BP, close in age to the Hekla-S/Kebister tephra (3720 cal yr BP), previously found in several sites in Scandinavia. Detailed geochemical analyses and dating is lacking for the mid-Holocene Sn-2 tephra in Iceland but it is likely that the geochemical composition is similar as the Sn-1 tephra. The LBA-2 tephra is tentatively correlated with the Sn-2 tephra and we also suggest that the 'x' tephra layer (ca 3500 BP) found in the Dyngjufjöll area, central Iceland (Sigvaldason et al. 1992) can be correlated with the Sn-2 tephra.
AUTHOR KEYWORDS: Jämtland;  Radiocarbon;  Snæfellsjökull;  Tephra;  Wiggle-match dating
DOCUMENT TYPE: Article
SOURCE: Scopus

Aziz, A.a , Ghnia, S.b 
Distribution of Infracambrian rocks and the hydrocarbon potential within the Murzuq and Al Kufrah basins, NW Africa
(2009) Geological Society Special Publication, (326), pp. 211-219. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75249101464&partnerID=40&md5=c5e1fa9d7ee9c30fc97e8173b6d00cef
AFFILIATIONS: Exploration Department, Exxon Mobil Libya, Tripoli, Libyan Arab Jamahiriya; 
Baker Hughes Geoscience, Tripoli, Libyan Arab Jamahiriya
ABSTRACT: This paper presents an overview of the distribution of the Infracambrian rocks within the Murzuq and Al Kufrah basins obtained by integrating existing data and new outcrop and subsurface data, and discusses the implications for the regional depositional setting and hydrocarbon potential. In the Murzuq Basin the Infracambrian units comprise volcaniclastics, metasediments and fineto medium-grained sandstones with an average thickness of 61 m, reflecting a proximal, clasticdominated depositional system. In the Al Kufrah Basin carbonate facies in Jabal Arkanu (eastern margin) indicate that the distal facies may become organic-rich. Interpreted seismic lines reveal Infracambrian graben systems similar to those found elsewhere that provide good hydrocarbon source rocks in petroliferous basins. © The Geological Society of London 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Cinque, A.a , Robustelli, G.b 
Alluvial and coastal hazards caused by long-range effects of Plinian eruptions: The case of the Lattari Mts. After the AD 79 eruption of Vesuvius
(2009) Geological Society Special Publication, (322), pp. 155-171. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-74949084364&partnerID=40&md5=032625ff9d181f594dec1324bf237290
AFFILIATIONS: Università degli Studi Federico II, Dipartimento di Scienze della Terra, Largo S. Marcellino 10, 80138 Naples, Italy; 
Università della Calabria, Dipartimento di Scienze della Terra, Via Pietro Bucci, 87036 Arcavacata di Rende, Cosenza, Italy
ABSTRACT: The Lattari Mountains (a limestone ridge about 20 km south of Vesuvius) received 1-2.5 m of fallout from the famous Plinian eruption of AD 79. As demonstrated by many residual outcrops of thick volcanoclastic debris-flow and alluvial deposits (referred to here as the Durece unit), the pyroclastic fall was soon followed by rapid erosion and landsliding that produced (1) decametre-scale aggradation of some narrow valley floors; (2) reactivation of alluvial fans; and (3) growth of new fan-deltas (extending as far as 500 m) at the coast. This response was primarily due to the steep topography of the area and the high erodability of the pyroclastic materials (light and cohesionless pumice fragments). Several geo-archaeological data indicate that the accelerated sedimentation had a duration of the order of decades and was followed by rapid dissection of the Durece unit deposits and fast dismantling by wave action of the newly created fan-deltas. This case highlights the need to consider the possibly catastrophic reaction of fluvial and coastal systems to large explosive eruptions, even in non-volcanic terrains at some distance from the volcano. © The Geological Society of London 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Witt, W.K.a , Mason, D.R.b , Hammond, D.P.c 
Archean Karari gold deposit, Eastern Goldfields Province, Western Australia: A monzonite-associated disseminated gold deposit
(2009) Australian Journal of Earth Sciences, 56 (8), pp. 1061-1086. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70449116191&partnerID=40&md5=fd1cd0a4b6bdf0f0dca12d3120d740f6
AFFILIATIONS: The Walter Witt Experience, 4/10 Field Street, Mt Lawley, WA 6050, Australia; 
Mason Geoscience, Greenhill, SA 5140, Australia; 
De Grey Mining Ltd, Suite 4, 100 Hay Street, Subiaco, WA 6008, Australia
ABSTRACT: The Karari gold deposit is situated in the Carosue sedimentary basin, 110 km northeast of Kalgoorlie, in the Archean Eastern Goldfields Superterrane of Western Australia. The Carosue basin is a late-tectonic accumulation of volcaniclastic sedimentary rocks that unconformably overlies a deformed granite-greenstone association. The sedimentary basin is intruded by numerous plutons and dykes of monzonite, lamprophyre and syenite and is cut by a swarm of post-intrusion faults with north-south orientations. Gold mineralisation at Karari occurs in a fault-bound zone of volcaniclastic sedimentary rocks that are intruded by monzonite porphyry and lamprophyre dykes. The hangingwall of the central mineralised zone is formed by the eastern intrusive complex, a porphyritic monzonite unit intruded by numerous dykes of monzonite porphyry, syenite porphyry and lamprophyre. The eastern intrusive complex is characterised by widespread potassic alteration and contains minor low-grade copper mineralisation. In the Karari pit, gold is associated with W and As, whereas Ag, Bi, Cu, Mo, Pb, Te and Zn form spatially distinct anomalous zones in the eastern intrusive complex and associated bounding faults. The central mineralised zone is interpreted as a downfaulted, higher-level exposure of the magmatic system represented by the eastern intrusive complex. Gold lodes are steep tabular zones of sodic alteration within a more extensive area of potassic alteration. Sodic alteration zones contain numerous veins and veinlets, which contain a variety of assemblages, several of which are mutually overprinting. Hematite occurs as a dusting in fine-grained albite and carbonate in the sodic alteration zones but is interpreted as a later (post-gold) event. Modelling using Hch software suggests that potassic alteration and low-grade copper mineralisation were caused by a high-temperature, saline fluid, probably derived from magmas of the eastern intrusive complex. The sodic alteration assemblage at Karari could not be duplicated but the results of other workers show that sodic alteration could have formed by reaction of quartzo-feldspathic rocks with a mesothermal, lowsalinity H2O-CO2 fluid. The data and observations described in this paper do not permit an unequivocal distinction between orogenic and orthomagmatic models for the gold mineralisation. © 2009 Geological Society of Australia.
AUTHOR KEYWORDS: Archean;  Gold;  Hydrothermal alteration;  Karari;  Mesothermal;  Modelling;  Monzonite;  Yilgarn Craton
DOCUMENT TYPE: Article
SOURCE: Scopus

Asiabanha, A.a , Ghasemi, H.b , Meshkin, M.c 
Paleogene continental-arc type volcanism in North Qazvin, North Iran: Facies analysis and geochemistry
(2009) Neues Jahrbuch fur Mineralogie, Abhandlungen, 186 (2), pp. 201-214. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-76249118660&partnerID=40&md5=c1ca328166c0ebc65045b3e4de50e88c
AFFILIATIONS: Department of Geology, Faculty of Science, Imam Khomeini International University, Qazvin, Iran; 
Faculty of Geosciences, Shahrood University of Technology, Shahrood, Iran; 
Payam-e-Noor University, Tehran, Iran
ABSTRACT: Paleogene volcanics in North Qazvin, which are equivalent to the Karaj Formation in the Alborz zone, may be distinguished into three main facies: 1) A volcaniclastic subaqueous fades forming two sub-facies: pyroclastic green tuffs (PGTs) in the lower parts of the succession and epiclastic variously colored tuffs (EVTs) in the upper parts. PGTs provide evidences of explosive eruptions in a shallow sedimentary basin, whereas EVTs were formed in a quiet sedimentary basin during middle-upper Eocene. 2) Lava facies including basic lava flows and dacitic dome are effusive subaerial products that extruded after uplifting and folding of the volcano-sedimentary basin due to the Pyrenean orogeny in the late Eocene. 3) Intrusive facies that are seen as dike swarms (mostly parallel dikes) and a monzogabbroic stock, intrude volcaniclastic facies. Based on the various facies, it can be stated that the volcanic style in the North Qazvin area is characterized by an initial explosive stage in the shallow sedimentary basin and continued to the effusive stage subaerially. Geochemically, the analyzed rocks belong to a high-K calcalkaline and shoshonitic series, and evolved by magmatic differentiation. Rare earth element (REE) patterns suggest a common source. Negative anomalies for high field strength elements (especially Nb and Ti), enrichment in light REEs, and positive K and Pb anomalies indicate that these rocks originated in relation to subduction beneath a continental arc. © by E. Schweizerbart'sche Verlagsbuchhandlung 2009.
AUTHOR KEYWORDS: Alborz;  Continental arc;  Magmatism;  Parallel dikes;  Pyroclastic;  Shoshonitic
DOCUMENT TYPE: Article
SOURCE: Scopus

Godoy, A.M.a , Manzano, J.C.b , de Araújo, L.M.B.c , da Silva, J.A.d 
Geological and structural frame of the Rio Apa Massif, southeastern of the Amazonian Craton (MS), Brasil [Contexto geológico e estrutural do Maciço Rio Apa, sul do Cráton amazônico - MS]
(2009) Geociencias, 28 (4), pp. 485-499. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77950643728&partnerID=40&md5=ad75c3ffb2c018d5f5d2d6d55ed542cd
AFFILIATIONS: Departamento de Petrologia e Metalogenia, Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, UNESP, Campus Rio Claro. Avenida 24A, 1515 - Bela Vista. CEP 13506-900. Rio Claro, SP, Brazil; 
Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, UNESP, Campus Rio Claro. Avenida 24A, 1515 - Bela Vista. CEP 13506-900. Rio Claro, SP, Brazil; 
Instituto de Ciências Ambientais e Desenvolvimento Sustentável, Universidade Federal da Bahia, Campus Universitário Reitor Edgard Santos, Rua Prof. José Seabra, s/n, CEP: 47805-100 begin_of_the_skype_highlighting              47805-100      end_of_the_skype_highlighting. Barreiras, BA, Brazil; 
Companhia Matogrossense de Mineração, METAMAT, Avenida Gonçalo Antunes de Barros, 2970 - Bairro Planalto. CEP 78.050-300. Cuiabá, MT, Brazil
ABSTRACT: Rio Apa Massif crops out in the Mato Grosso do Sul state and corresponds to the southeastern portion of the Amazonian Craton dominantly Paleoproterozoic in age. Rio Apa Complex is oldest and it is composed mainly by migmatitic orthogneisses, beyond amphybolites, tonalities and granodiorite. Alto Tererê Group is composed by schists, biotitemuscovite gneisses and micaceous quartzites generally rich in garnets, beyond metabasic rocks of low amphibolite facies. The Amoguijá Group is constituted by Alumiador Intrusive Suite, which is represented by a sieno to monzogranitic batholith and Serra da Bocaina Volcanic Suite composed of volcanoclastic rocks of alkali riolites to monzoriolites compositions and pyroclastic products. Overlaying towards East and South occurs Neoproterozoic metasedimentary rocks from the Paraguai Folded Belt (Cuiabá, Corumbá and Jacadigo Groups - Urucum Formation). Structural-metamorphic framewok is identified by five deformational phases but the actual tectonic and metamorphic structure shows the superposed tectonic array of the Paraguai Folded Belt. Rocks from Rio Apa Complex, Alto Tererê Group and Amoguijá Group record an older structural evolution defined by (Dn-1 and Dn). The deformational phases (Dn+1 and Dn+2) are visible mainly in rocks of Paraguai Folded Belt beyond the last deformation (Dn+3) that imprints all sequences.
AUTHOR KEYWORDS: Amazonian craton;  Petrography;  Rio apa massif;  Structural evolution
DOCUMENT TYPE: Article
SOURCE: Scopus

Tshibubudze, A.a , Hein, K.A.A.a , Marquis, P.b 
The Markoye Shear Zone in NE Burkina Faso
(2009) Journal of African Earth Sciences, 55 (5), pp. 245-256. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-75149137472&partnerID=40&md5=4c52f5696cd8cdaa9e5d2d95c3ae729b
AFFILIATIONS: School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. WITS, Johannesburg, 2050, South Africa; 
Orezone Resources Inc., 290 Picton Ave, Suite 201, Ottawa, Ont. K1Z 8P8, Canada
ABSTRACT: Birimian supracrustal sequences in NE Burkina Faso are dominated by meta-volcaniclastic greywacke, intercalated meta-conglomerate, siltstone and shale. The sequences where subjected to two phases of deformation and contact metamorphosed to hornblende-hornfels facies during emplacement of pyroxenite-gabbro-norite (Yacouba Mafic complex), granodiorite-tonalite (Tin Taradat granodiorite-tonalite) and dolerite dykes. Structural studies indicated that the NE-trending, first-order crustal-scale Markoye Shear Zone (MSZ; Markoye Fault of [Jeambrun, M., Delfour, J., Gravost, M., 1970. Carte géologique de L'Oudalan. Bureau De Recherches Geologiques et Miniéres, Burkina Faso.]) has undergone at least two phases of reactivation concomitant to two phases of regional deformation. The first phase of deformation, D1, resulted in the formation of NNW-NW trending folds and thrusts during dextral-reverse displacement on the MSZ. The deformation is termed the Tangaean Event and predates the Eburnean Orogeny. D2 phase involved a period of SE-NW crustal shortening and sinistral-reverse displacement on the MSZ, and is correlated to the Eburnean Orogeny ∼2.1 Ga. Deformation in D2 is characterised by NE-trending regional folds (F2) and a pervasive NE-trending foliation (S2-C to S2). Within the MSZ, deformation is characterised by NNE-trending zones of mylonite that are bordered in the hangingwall and footwall by pseudotachylite veins. Buck quartz-carbonate veins and quartz cataclasite veins crosscut the mylonite zones and are, in turn, crosscut by quartz-chlorite-(muscovite) shears that formed during reactivation of the MSZ late in D2. Several generations of veins are recognised at the Essakane main deposit (EMZ): Arsenopyrite-pyrite-gold mineralization in quartz veins formed in D1 during metasomatic alteration of the host rocks; Vein-stockwork gold mineralization is interpreted to have formed late in D2. © 2009 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Birimian;  Burkina Faso;  Gold;  Structure;  Tectonics;  West African Craton
DOCUMENT TYPE: Article
SOURCE: Scopus

Adams, C.J.a , Cluzel, D.b  c , Griffin, W.L.d 
Detrital-zircon ages and geochemistry of sedimentary rocks in basement Mesozoic terranes and their cover rocks in New Caledonia, and provenances at the Eastern Gondwanaland margin
(2009) Australian Journal of Earth Sciences, 56 (8), pp. 1023-1047. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70449122798&partnerID=40&md5=f6142d64e536af5c7dac43d46b4422d8
AFFILIATIONS: GNS Science, Private Bag 1930, Dunedin, New Zealand; 
University of Orleans, CRNS/INSU, University Francois Rabelais-Tours, Institut des Sciences de la Terre d'Orléans, UMR 6113, France; 
University of New Caledonia, PPME, EA 3325, Noumea, New Caledonia; 
ARC Key Centre for Geochemical Evolution and Metallogeny of Continents, Department of Earth and Planetary Sciences, Macquarie University, North Ryde, NSW 2109, Australia
ABSTRACT: Geochemical and Sr-Nd isotope data for Mesozoic greywackes of New Caledonia terranes, indicate a forearc tectonic environment at the Eastern Gondwanaland margin, but they support only minor continental influences. Detrital-zircon U-Pb age patterns for the greywackes in these terranes similarly reflect an active-margin tectonic environment of Late Triassic, Late Jurassic, and in particular mid-Cretaceous, depocentres which comprise much contemporaneous volcanic detritus, but also include minor sediment inputs from Precambrian-Early Paleozoic continental clastic rocks. The contemporary volcanic sources are probably now hidden within a former hinterland to New Caledonia, such as Lord Howe Rise or Marion Plateau. The older, continental sediment sources were probably in northeastern-most Queensland, and beyond the northern extremity of the New England Orogen. Such sediments could have been supplied on long rivers, and submarine longshore current systems outboard of the orogen. Alternatively, the depocentres could have been consolidated close to the contemporary Gondwanaland margin and then tectonically transported, as suspect terranes, southwards in Early Cretaceous times to their present New Caledonia position. © 2009 Geological Society of Australia.
AUTHOR KEYWORDS: Detrital zircon;  Geochemistry;  Geochronology;  Gondwanaland;  Mesozoic;  Neodymium isotopes;  New Caledonia;  Strontium isotopes;  Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Roldán-Quintana, J.a , McDowell, F.W.b , Delgado-Granados, H.c , Valencia-Moreno, M.a 
East-west variations in age, chemical and isotopic composition of the Laramide batholith in southern Sonora, Mexico
(2009) Revista Mexicana de Ciencias Geologicas, 26 (3), pp. 543-563. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77949594001&partnerID=40&md5=29da88c3354acc6f52baf7e93835a036
AFFILIATIONS: Estación Regional del Noroeste, Instituto de Geología Universidad Nacional Autónoma de México, Apartado Postal 1039, 83000 Hermosillo, Sonora, Mexico; 
Department of Geological Sciences, The University of Texas at Austin, Austin TX 78712, United States; 
Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito Exterior Ciudad Universitaria, 04510 México, D. F., Mexico
ABSTRACT: We examined an east-west transect from the Gulf of California to the volcanic province of the Sierra Madre Occidental (28°30'N). The transect is divided into three geologic regions: 1) The coastal region (COR) is characterized by scattered exposures of Laramide plutons lying beneath the modern and late Tertiary sediments. No outcrops of the volcanic component (Tarahumara Formation) were found there; 2) The central region (CER) is dominated by widespread outcrops of both the Laramide batholith (LB) and coeval volcanic and volcaniclastic rocks. Exposures of intrusive contacts confirm the close relationship of the plutonic and volcanic rocks there; 3) The eastern segment (SMOc) with exposures of the Laramide arc (LA) that are mostly concealed by the Tertiary Sierra Madre Occidental volcanic rocks. The plutonic rocks in the COR are granodiorite and tonalite and, further inland, they change to granodiorite and granite. Extensive hydrothermal alteration largely obscures textures in the volcanic rocks, but fresh samples range from andesite, dacite and less rhyolite. Chemically, the plutons are medium-K to high-K calc-alkaline, LREE-enriched and with relatively minor europium anomalies. K-Ar and U/Pb dating shows that plutons are older (79-83 Ma) to the west and younger to the east, where age ranges between 55 and 65 Ma throughout the remainder of the transect. The coeval volcanic facies yielded zircon U/Pb ages of 60 Ma, and 70 to 90 Ma within the CER. A younger pulse at ~50 Ma is present in the west of the SMOc region. Radiogenic Sr and Nd isotope values range from initial 87Sr/86Sr 0.70547 to 0.70715 and εNd varies from -3.3 to -6.3. All of these results are consistent with development of a subduction-related magmatic arc that was emplaced within mature continental crust. The present-day width of the arc is &gt;300 km, which suggests development of a low-angle subduction configuration that produced a significant volume of magmatism. Although the age decreases with the distance to the plate margin, the trend is not regular, and the activity between 55 and 65 Ma is at least 200 km in width. The results also support a configuration in which the Laramide arc of the mainland of southern Sonora is a continuation of the Peninsular Ranges batholith of Baja California. However, the LA shows significant contrasts with the batholith of southern Sinaloa, which is narrower and has a larger age range. The southern Sinaloa batholith also has compositional and isotopic characteristics consistent with emplacement within a younger and less mature crustal domain (Guerrero terrane).
AUTHOR KEYWORDS: Geochronology;  Laramide batholith;  Mexico;  Southern Sonora;  Volcanic arc
DOCUMENT TYPE: Article
SOURCE: Scopus

Onofrio, V.a , Tropeano, M.a  b , Festa, V.c , Moretti, M.a  b , Sabato, L.a  b 
Quaternary transpression and lacustrine sedimentation in the San Lorenzo area (Sant'Arcangelo Basin, Italy)
(2009) Sedimentary Geology, 222 (1-2), pp. 78-88. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70449107072&partnerID=40&md5=50270cc3ed4c2428e309b7e3a00a0430
AFFILIATIONS: Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy; 
Centro Interdipartimentale di Ricerca per il Rischio Sismico e Vulcanico, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy; 
Dipartimento Geomineralogico, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy
ABSTRACT: Quaternary lacustrine sedimentation of the San Lorenzo Succession represents one of the more recent steps in the evolution of the northern part of the Sant'Arcangelo Basin. The latter is a large Pliocene to Pleistocene wedge-top depozone of the southern Apennines foreland-basin system that developed close to the front of the thrust belt in southern Italy. The lower to middle Pleistocene lacustrine deposits are composed of siltstone and claystone interbedded with sandstone, carbonate and volcaniclastic beds, arranged in fining-upward sequences. The overall stratigraphical, sedimentological, and structural data collected demonstrate that the San Lorenzo lacustrine deposits formed when the northern sector of the Sant'Arcangelo Basin was undergoing tectonic deformation. In particular, new data reveal the presence of strike-slip syndepositional faults. These faults belong to positive flower-type structures, which developed in a left-lateral transpressive tectonic regime characterized by a E-W horizontal component of shear stress. The lacustrine deposits recorded the activity of these faults showing growth structures represented mainly by gentle synclines, as well as other minor folds. The tectonic activity of the main faults formed an endorheic area with at least two different depocentres accumulating lacustrine successions. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Lacustrine deposits;  Pleistocene;  Sant'Arcangelo Basin;  Southern Italy;  Strike-slip tectonics
DOCUMENT TYPE: Article
SOURCE: Scopus

Williams, N.C.a  b 
Mass and magnetic properties for 3D geological and geophysical modelling of the southern Agnew-Wiluna Greenstone Belt and Leinster nickel deposits, Western Australia
(2009) Australian Journal of Earth Sciences, 56 (8), pp. 1111-1142. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70449381335&partnerID=40&md5=69d54e70e7edfbd81caa6d644768b77a
AFFILIATIONS: Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada; 
Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia
ABSTRACT: Physical property measurements provide a critical link between geological observations and geophysical measurements and modelling. To enhance the reliability of gravity and magnetic modelling in the Yilgarn Craton's Agnew-Wiluna Greenstone Belt, mass and magnetic properties were analysed on 157 new rock samples and combined with an existing corporate database of field measurements. The new samples include sulfide ore, serpentinised and olivine-bearing ultramafic host-rocks, granitoid, and felsic and mafic volcanic and volcaniclastic country rock. Synthesis of the data provides a useful resource for future geophysical modelling in the region. Several rock types in the region have sufficiently distinct physical properties that a discriminant diagram is proposed to facilitate a basic classification of rock types based on physical properties. However, the accumulation of emplacement, metamorphic, hydrothermal and structural processes has complicated the physical properties of the rocks by imposing duplicate and sometimes opposing physical property trends. The data confirm that massive sulfide and ultramafic rocks have the most distinctive mass and magnetic properties but with variability imposed by their complex history. Sulfide content imposes the strongest control on densities, but can only be identified when comprising >10 vol% of the rock. The pyrrhotiterich Ni-sulfide assemblages generally have similar magnetic properties to the host ultramafic rocks, but can have much lower susceptibilities where the thermal history of the rocks has favoured development of hexagonal pyrrhotite over monoclinic pyrrhotite. In ultramafic rocks that contain <10 vol% sulfides, density and susceptibility are primarily controlled by serpentinisation, with olivine breaking down to serpentine and magnetite in the presence of water. Serpentinisation dramatically lowered densities and increased susceptibilities, but had limited influence on the intensity of remanent magnetisation. All ultramafic rocks contain multidomain magnetite, and most contain low coercivity grains prone to overprinting by in situ viscous remanent magnetisation or drilling-induced isothermal remanent magnetisation during extraction. Despite the low coercivities, Koenigsberger ratios of 1-20 are observed indicating that viscous remanent magnetisation aligned parallel to the present Earth field must be considered in any magnetic modelling. It is also noted that coarser-grained intrusive varieties of all rock types (e.g. granite, gabbro) show remanent magnetisation intensities 1-2 orders of magnitude greater than their extrusive equivalents (felsic and basaltic volcanics). © 2009 Australian Government.
AUTHOR KEYWORDS: Agnew-Wiluna Greenstone Belt;  Density;  Magnetic susceptibility;  Nickel;  Remanent magnetisation;  Serpentinisation;  Sulfide;  Ultramafic
DOCUMENT TYPE: Article
SOURCE: Scopus

Benedetto, J.L., Vaccari, N.E., Waisfeld, B.G., Sánchez, T.M., Foglia, R.D.
Cambrian and Ordovician biogeography of the South American margin of Gondwana and accreted terranes
(2009) Geological Society Special Publication, (325), pp. 201-232. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-74949142596&partnerID=40&md5=90b5614c5b63b706d26bdf8515d6b274
AFFILIATIONS: CICTERRA-CONICET, Centro de Investigaciones Paleobiológicas, Facultad de Ciencias Exactas, Av. Velez Sarsfield 299, X5000JJC Córdoba, Argentina
ABSTRACT: Three main geological units were involved in the Early Palaeozoic history of South America: (1) autochthonous intracratonic and pericratonic basins developed around the Gondwana basement (e.g. the Central Andean basin, CAB); (2) volcano-sedimentary basins marginal to Gondwana (e.g. Famatina and Puna volcanic belts); (3) crustal fragments accreted to the Andean margin through the Palaeozoic (e.g. Precordillera terrane). Knowledge of brachiopods, trilobites and bivalves has increased substantially over recent years, leading to the assembly of a more complete dataset. Furongian-Tremadocian trilobites from Famatina, western Puna and the CAB are mostly widespread forms (Olenid Fauna); however, the record of Amzasskiella and Onychopyge suggests a connection with East Gondwana, Siberia and Kazakhstan. At that time, the Central Andean brachiopods and bivalves show links with Iberia, Bohemia and North Africa. Floian trilobites from these regions show a complex array of endemic and peri-Gondwanan forms, indicative of relatively free migration for some taxa around Gondwana. Coeval brachiopods from Famatina and western Puna volcaniclastic rocks are of Celtic type, having some taxa in common with coeval faunas from south Peru, which would support the existence of a long and nearly continuous volcanic arc marginal to the Iapetus Ocean. Cambrian to Middle Ordovician platform carbonate rocks are confined to the Precordillera basin. Trilobites from the Lower and Upper Cambrian limestones of the Precordillera include key genera indicating Laurentian affinities (Arcuolenellus, Madarocephalus, Plethopeltis). Associated rhynchonelliformean brachiopods (e.g. Nisusia, Wimanella) are also typical of low-latitude palaeocontinents. Trilobites from the upper Tremadocian-Floian sequences of the Precordillera match those of the Bathyurid Fauna, whereas associated brachiopods include a high percentage of Laurentian taxa. From the Floian, a biotic exchange with Gondwana and Baltica becomes evident in the Precordilleran trilobite faunas. By Darriwilian times, Precordilleran brachiopods form a well-defined low-latitude realm, but numerous Celtic and Baltic taxa immigrated into the basin. By the Sandbian, affinities of Precordilleran brachiopods shift to West Gondwanan (North Africa, Armorica, Perunica and central Andes), probably reflecting the accretion of the Precordillera (Cuyania) terrane to the proto-Andean margin, although some mixed faunas persist. The low-richness CAB brachiopod, bivalve and trilobite assemblages display stronger 'Mediterranean' affinities than those from the Precordillera. In summary, there are abundant palaeontological data supporting the view that the Precordillera is a Laurentian-derived far-travelled microcontinent accreted to Gondwana during the Early Palaeozoic. A new early Middle Ordovician reconstruction of the southern and central proto-Andean margin is based on recently published geological data as well as the new palaeontological evidence summarized in this paper. © The Geological Society of London 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Sacchi, M.a , Molisso, F.a , Violante, C.a , Esposito, E.a , Insinga, D.a , Lubritto, C.b , Porfido, S.a , Tóth, T.c  d 
Insights into flood-dominated fan-deltas: Very high-resolution seismic examples off the Amalfi cliffed coasts, eastern Tyrrhenian Sea
(2009) Geological Society Special Publication, (322), pp. 33-71. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-74949106158&partnerID=40&md5=3cfe2fa68a2006aaf8e06d5c8ff6ad81
AFFILIATIONS: Istituto per l'Ambiente Marino Costiero (IAMC)-CNR, Napoli, Calata P.ta di Massa, Porto di Napoli, 80133-Napoli, Italy; 
Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Via Vivaldi, 43-81100 Caserta, Italy; 
Department of Geophysics, Eötvös Loránd University, Pázmány Péter, Sétány 1/C, H-1117 Budapest, Hungary; 
Geomega Ltd., Mester u. 4, 1095 Budapest, Hungary
ABSTRACT: A high-resolution (IKB-Seistec) seismic survey calibrated with gravity-core data, off the Amalfi coast, a rocky coastal area on the southern side of the Sorrento Peninsula (Italy), documents the internal stratigraphic architecture of a series of small fan-deltas that develop at the mouth of major bedrock streams. The fan-delta system mostly postdates the Plinian eruption of Vesuvius of AD 79 and displays various phases of development associated with periods of high sediment supply from the adjacent river basins. During these periods landscape-mantling loose pyroclastic deposits (mostly air-fall tephra from Vesuvius) were quickly eroded and delivered to the continental shelf by sheet wash and flash flood events. Depositional processes on the foresets were dominated by sediment gravity flows originating from hyperpycnal river flow and pyroclastic fall deposits. This in turn created favourable conditions for sea-floor instability, soft sediment failure, slumping and sliding, which characterize the deltaic stratigraphic architecture. The intermittently increased sediment yield during the various phases of the evolution of the fan-delta system was probably influenced also by the morphoclimatic regime. This may have resulted in varying rates of progradation of the delta foresets, tentatively correlated with the main climatic oscillations of the last 2000 years. The Amalfi fan-delta system represents a small-scale analogue for larger flood-dominated fan-deltas of the world and may be regarded as a useful example for a better understanding of inner-shelf, mixed siliciclastic-volcaniclastic fan-delta systems in the stratigraphic record. © The Geological Society of London 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Underwood, M.B., Saito, S., Kubo, Y.
Nantroseize Stage 2: Subduction inputs
(2009) Integrated Ocean Drilling Program: Preliminary Reports, (322), pp. 1-90. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77749254659&partnerID=40&md5=061671a24fbe18868285a72f6e2fbc60
ABSTRACT: Integrated Ocean Drilling Program (IODP) Expedition 322 is part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and was designed to document characteristics of incoming sedimentary strata and igneous basement prior to their arrival at the subduction front. To accomplish these objectives, coring was conducted at two sites in the Shikoku Basin on the subducting Philippine Sea plate. Site C0011 is located on the northwest flank of a prominent bathymetric high (the Kashinosaki Knoll), whereas Site C0012 is located near the crest of the knoll. The resulting data, which include logging while drilling during IODP Expedition 319, provide a wealth of new information on presubduction equivalents of the seismogenic zone. Unfortunately, coring at Site C0011 began at 340 m core depth below seafloor (CSF) and failed to reach the total depth target because of premature destruction of the drill bit at 876 m CSF. Coring at Site C0012, however, penetrated almost 23 m into igneous basement and recovered the sediment/basalt interface intact at 537.81 m CSF. The age of basal sediment (reddish-brown pelagic claystone) is >18.9 Ma. This recovery of basement was a major achievement, as was the comprehensive integration of core-log-seismic data at Site C0011. The merger of lithofacies and age-depth models from the two sites spans across the Shikoku Basin from an expanded section (Site C0011) to a condensed section (Site C0012) and captures all of the important ingredients of basin evolution, including a heretofore unrecognized interval of late Miocene tuffaceous and volcaniclastic sandstone designated the middle Shikoku Basin facies. An older (early-middle Miocene) turbidite sandstone/siltstone facies with mixed detrital provenance occurs in the lower Shikoku Basin; this unit may be broadly correlative with superficially similar Miocene turbidites on the western side of the basin. When viewed together, the two sites around the Kashinosaki Knoll not only demonstrate how basement relief influenced rates of hemipelagic and turbidite sedimentation in the Shikoku Basin, they also build the complete lithostratigraphic template on which all of the postexpedition laboratory results can be placed. Those forthcoming details will include mineral and volcanic ash composition, geotechnical properties, frictional properties, and hydrological properties. Another triumph came from geochemical analyses of pore water and hydrocarbons at Site C0012. Unlike other so-called reference sites in the Nankai Trough, pore fluids on top of the basement high show clear evidence of a seawaterlike source, with chlorinity values increasing toward basement because of hydration reactions and diffusion; the fluids are largely unchanged by the effects of focused flow and/or in situ dehydration reactions associated with rapid burial beneath the trench wedge and frontal accretionary prism. Thus, Site C0012 finally pro-vides a reliable geochemical reference site for the subduction zone.
DOCUMENT TYPE: Article
SOURCE: Scopus

Polat, A.a , Frei, R.b  c , Fryer, B.a  d , Appel, P.W.U.e 
The origin of geochemical trends and Eoarchean (ca. 3700 Ma) zircons in Mesoarchean (ca. 3075 Ma) ocelli-hosting pillow basalts, Ivisaartoq greenstone belt, SW Greenland: Evidence for crustal contamination versus crustal recycling
(2009) Chemical Geology, 268 (3-4), pp. 248-271. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350622052&partnerID=40&md5=d1851fc15f6688e932a57f9fcabed5f1
AFFILIATIONS: Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ont. N9B 3P4, Canada; 
Institute of Geography and Geology, University of Copenhagen, 1350 Copenhagen, Denmark; 
Nordic Center for Earth Evolution, NordCEE, Denmark; 
Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ont. N9B 3P4, Canada; 
Geological Survey of Denmark and Greenland, 1350 Copenhagen, Denmark
ABSTRACT: The Mesoarchean Ivisaartoq greenstone belt consists of tholeiitic pillow basalts, picrites, boninites, gabbroic to dioritic dykes and sills, actinolite schists and serpentinites. In addition, the belt includes volumetrically minor siliceous volcaniclastic sedimentary rocks, cherts, biotite schists, and quartzitic gneisses. Siliceous volcaniclastic rocks yield an average U-Pb zircon age of 3075 ± 15 Ma, and pillow basalts and gabbros yield a Sm-Nd errorchron age of 3080 ± 160 Ma, constraining the maximum age of the belt. The Ivisaartoq rocks underwent high-temperature seafloor hydrothermal alteration, resulting in extensive epidote-diopside calc-silicate metasomatism. Th-REE-Nb systematics of the least metasomatized volcanic rocks are consistent with a supra-subduction zone geodynamic setting, displaying a trend projecting from mid-ocean ridge basalt (MORB) field to island arc basalt (IAB) field. This trend is interpreted as reflecting a transition from the depleted upper mantle to a subarc mantle wedge following the initiation of intra-oceanic subduction and arc migration. Many pillow basalts in the Ivisaartoq greenstone belt contain numerous millimetre- to centimetre-long white polycrystalline ellipsoidal inclusions, called 'ocelli', set in a dark green mafic matrix (basaltic host). On the basis of new major and trace element, Nd isotope, and petrographic data, we re-interpret the origin of these inclusions and suggest that they were derived from the melting of hydrated mafic to ultramafic rocks in the lower oceanic crust during magma-crust interaction. Some pillow basalts contain rare small inherited magmatic zircons revealing Eoarchean (3706 ± 8 to 3717 ± 4 Ma) 207Pb206Pb ages. In the least metasomatized pillow basalts, and gabbros and diorites there is a strong negative correlation between initial Nd isotopic composition (εNd = + 0.76 to + 3.10) and depleted mantle model ages (TDM = 3100-3800 begin_of_the_skype_highlighting              3100-3800      end_of_the_skype_highlighting Ma). Post-magmatic metasomatic alteration can be ruled out as the cause of this negative correlation, suggesting the contamination of the Ivisaartoq rocks, or their mantle source, by Eoarchean (~ 3700 Ma) continental crust or sediments derived from such crust. Four possible processes of crustal contamination might have taken place during or prior to the emplacement of the Ivisaartoq belt: (1) interaction with continental crust during magma ascent; (2) mixing between the depleted upper mantle and recycled sediments derived from Eoarchean continental crust; (3) mixing between the depleted upper mantle and delaminated lower continental crust; and (4) assimilation of continentally-derived sediments during eruption. It is unlikely that recycled Eoarchean zircons and their host rocks could have survived through multiple events of partial melting in the Mesoarchean upper mantle. A tectonic slice of metasedimentary rocks exposed between the Ivisaartoq belt and the Eoarchean (3600-3870 begin_of_the_skype_highlighting              3600-3870      end_of_the_skype_highlighting Ma) Isukasia terrane contains magmatic zircon grains up to 3800 Ma old. Accordingly, we argue that Eoarchean zircons are likely to have been derived from the protoliths of these metasedimentary rocks. The negative correlation between initial εNd and TDM in pillow basalts, gabbros and diorites, however, can be better explained by contamination of the mantle source through hydrous melts and/or fluids, derived from Mesoarchean subducted (recycled) sediments, than by contamination at the surface. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Archean;  Continental crust;  Greenstone;  Mantle;  Ocelli;  Recycling
DOCUMENT TYPE: Article
SOURCE: Scopus

Hayman, P.C.a , Cas, R.A.F.a , Johnson, M.b 
Characteristics and alteration origins of matrix minerals in volcaniclastic kimberlite of the Muskox pipe (Nunavut, Canada)
(2009) Lithos, 112, pp. 473-487. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749094710&partnerID=40&md5=634d6a85d4fe7147a7507f094456297b
AFFILIATIONS: School of Geosciences, Monash University, PO Box 28E, Vic. 3800, Australia; 
MDJ Consulting, 2021 Berkshire Crescent, Coquitlam, BC V3E 3N5, Canada
ABSTRACT: The matrix of volcaniclastic kimberlite (VK) from the Muskox pipe (Northern Slave Province, Nunavut, Canada) is interpreted to represent an overprint of an original clastic matrix. Muskox VK is subdivided into three different matrix mineral assemblages that reflect differences in the proportions of original primary matrix constituents, temperature of formation and nature of the altering fluids. Using whole rock X-ray fluorescence (XRF), whole rock X-ray diffraction (XRD), microprobe analyses, back-scatter electron (BSE) imaging, petrography and core logging, we find that most matrix minerals (serpentine, phlogopite, chlorite, saponite, monticellite, Fe-Ti oxides and calcite) lack either primary igneous or primary clastic textures. The mineralogy and textures are most consistent with formation through alteration overprinting of an original clastic matrix that form by retrograde reactions as the deposit cools, or, in the case of calcite, by precipitation from Ca-bearing fluids into a secondary porosity. The first mineral assemblage consists largely of serpentine, phlogopite, calcite, Fe-Ti oxides and monticellite and occurs in VK with relatively fresh framework clasts. Alteration reactions, driven by deuteric fluids derived from the juvenile constituents, promote the crystallisation of minerals that indicate relatively high temperatures of formation (> 400 °C). Lower-temperature minerals are not present because permeability was occluded before the deposit cooled to low temperatures, thus shielding the facies from further interaction with fluids. The other two matrix mineral assemblages consist largely of serpentine, phlogopite, calcite, +/- diopside, and +/- chlorite. They form in VK that contains more country rock, which may have caused the deposit to be cooler upon emplacement. Most framework components are completely altered, suggesting that larger volumes of fluids drove the alteration reactions. These fluids were likely of meteoric provenance and became heated by the volcaniclastic debris when they percolated into the VK infill. Most alteration reactions ceased at temperatures > 200 °C, as indicated by the absence or paucity of lower-temperature phases in most samples, such as saponite. Recognition that Muskox VK contains an original clastic matrix is a necessary first step for evaluating the textural configuration, which is important for reconstructing the physical processes responsible for the formation of the deposit. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Deuteric fluids;  Fe-Ti oxides;  Kimberlite alteration;  Matrix overprint;  Meteoric fluids;  Serpentine
DOCUMENT TYPE: Article
SOURCE: Scopus

Gernon, T.M.a  b , Gilbertson, M.A.c , Sparks, R.S.J.a , Field, M.a 
The role of gas-fluidisation in the formation of massive volcaniclastic kimberlite
(2009) Lithos, 112, pp. 439-451. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749088762&partnerID=40&md5=20bce607139f83e6c055e2450b6047b4
AFFILIATIONS: Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom; 
Department of Geology, Trinity College, Dublin, 2, Ireland; 
Department of Mechanical Engineering, University of Bristol, BS8 1TR, United Kingdom
ABSTRACT: Massive volcaniclastic kimberlite (MVK) deposits are a volumetrically important constituent in most kimberlite diatremes. MVKs are typically characterised by their uniform texture and homogeneous composition, and previous studies suggest that they exhibit little appreciable internal variation. However, new field results from the Venetia K1 diatreme (South Africa) show that MVK displays significant changes over metre-scales. The textural characteristics and large- and small-scale structure of the deposits are described and interpreted as being due to fluidisation. Laboratory experiments of tapered fluidised beds demonstrate how they are heterogeneous, with fluidisation and mixing limited to the centre of the bed. Marginal wedge-shaped regions remain unfluidised. The unfluidised regions are internally laminated and slip downwards when a high proportion of the bed is fluidised. The observations also demonstrate how fluctuations in gas velocity can produce steep internal boundaries between laminated and well-mixed regions. Data consistent with gas-fluidisation in MVK deposits includes the massive structure, uniform distribution of lithic clasts, presence of steep internal contacts, dominantly sub-vertical crystal fabrics across the vent, occurrence of surface-derived material along the tapered diatreme walls, and the presence of degassing structures. We propose that the overall structure of the Venetia K1 diatreme-fill is consistent with a multi-stage fluidised emplacement, which involved (1) strong initial fluidisation that caused thorough mixing of juvenile and lithic material; (2) a gradual step-wise decrease in gas flux, that produced nested pipe-like sequences; and (3) migration of the narrow fluidised column towards the steep eastern diatreme wall. The occurrence of (4) degassing structures in MVK deposits across the vent is consistent with an overall rapid transition from high to low degrees of fluidisation towards the end of the eruption. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Degassing;  Diatreme;  Fluidisation;  Kimberlite;  Venetia;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

van Straaten, B.I.a , Kopylova, M.G.a , Russell, J.K.a , Webb, K.J.b , Smith, B.H.S.a  c 
Stratigraphy of the intra-crater volcaniclastic deposits of the Victor Northwest kimberlite, northern Ontario, Canada
(2009) Lithos, 112, pp. 488-500. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749105666&partnerID=40&md5=367633d2c61b2f56995dca7b8565426d
AFFILIATIONS: Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada; 
De Beers Canada Inc. Exploration Division, 65 Overlea Blvd., Suite 400, Toronto, Ont. M4H 1P1, Canada; 
Scott-Smith Petrology Inc., 2555 Edgemont Blvd, North Vancouver, BC V7R 2M9, Canada
ABSTRACT: The Victor Northwest (VNW) kimberlite is one of several steep-sided pipes in the Victor kimberlite complex. In this paper detailed logging of ~ 4.2 km of drill core and petrographic studies of hundreds of samples and thin sections are used to reconstruct the intra-crater stratigraphy of the VNW kimberlite and to constrain the emplacement history of the pipe. The results show that the VNW pipe comprises numerous contrasting small-volume volcanic facies, including dark and competent kimberlite, sedimentary country rock breccias, pyroclastic kimberlite and resedimented volcaniclastic kimberlite. We interpret that the VNW pipe was formed by two separate eruption cycles. During the first eruption cycle, the main VNW crater is excavated and partly filled. The second eruption cycle excavates a smaller nested crater within the existing lithified pipe fill. Both eruption cycles can be subdivided into three comparable stages. The first stage in both cycles comprises a highly explosive eruption involving crater excavation and deposition of pyroclastic kimberlite. The eruption products contain abundant broken olivines, small angular country rock fragments and kimberlite ash. All these features indicate high degrees of fragmentation resulting from high eruption intensities. The high proportion of country rock fragments in these deposits suggests continuous pipe wall erosion. The second stage in both cycles is represented by dark and competent deposits, which have low country rock fragment abundances and mostly intact olivines. Based on contact relationships and textures within these units it is suggested that these rock types are formed by lower energy eruptions, during which no major pipe wall erosion took place. The eruption came to an end during the third and last stage. In both cycles, the uppermost deposits record resedimentation of kimberlite by water. Major pipe wall collapse results in the formation of voluminous sedimentary country rock breccia deposits that cap all previous deposits. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Eruption cycle;  Explosivity;  Kimberlite pipe;  Pyroclastic kimberlite;  Volcanic stratigraphy
DOCUMENT TYPE: Article
SOURCE: Scopus

Crawford, B.a , Hetman, C.b , Nowicki, T.b , Baumgartner, M.b , Harrison, S.a 
The geology and emplacement history of the Pigeon kimberlite, EKATI Diamond Mine, Northwest Territories, Canada
(2009) Lithos, 112, pp. 501-512. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749091993&partnerID=40&md5=e5d55dc78d07e0d102f8bbd1b46139d8
AFFILIATIONS: BHP Billiton Diamonds Inc., 1102, 4920-52nd Street, Yellowknife, North. Territ. X1A 3T1, Canada; 
Mineral Services Canada Inc., 205-930 Harbourside Drive, North Vancouver, BC V7P 3S7, Canada
ABSTRACT: The Pigeon kimberlite is located approximately 6 km to the northwest of the Koala cluster of the EKATI Diamond Mine, and is presently one of ten kimberlite occurrences in the EKATI resource development plan. It was emplaced along a regional lithological contact between syn-Yellowknife Supergroup granitoid rocks and Yellowknife Supergroup metasedimentary rocks that were covered by a now eroded veneer of poorly consolidated muddy sediments. Detailed age dating has not been undertaken, however the emplacement age is inferred from sedimentary xenoliths present within the pipe to range between 45-75 Ma. Pigeon is a small kimberlite body, estimated to be approximately 3.5 ha at surface, consisting of a steep-sided pipe that can be separated into four main geological domains that are characterized by contrasting textures, different diamond characteristics and unique mineral abundance and compositional signatures. The uppermost portion of the body consists of mud-rich resedimented volcaniclastic kimberlite that was formed by the deposition of extra crater deposits by debris flow type processes into an open diatreme. Texturally complex kimberlite is present within the lower portion of the kimberlite and includes rocks that display a range of features consistent with coherent (magmatic) and less common volcaniclastic (fragmental) rocks. This texturally complex zone is interpreted to represent a clastogenic deposit formed by a low energy eruption within an open diatreme. © 2009.
AUTHOR KEYWORDS: Clastogenic;  Coherent;  EKATI;  Kimberlite emplacement;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Harvey, S.a , Kjarsgaard, B.b , McClintock, M.c , Shimell, M.a , Fourie, L.a , Plessis, P.D.a , Read, G.a 
Geology and evaluation strategy of the Star and Orion South kimberlites, Fort à la Corne, Canada
(2009) Lithos, 112, pp. 47-60. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749088942&partnerID=40&md5=9e42ee841aa19c4fe5a8eba917794099
AFFILIATIONS: Shore Gold Inc., 300-224 4th Avenue South, Saskatoon, Sask. S7K 5M5, Canada; 
Geological Survey of Canada, 601 Booth Street, Ottawa, Ont. K1A 0E8, Canada; 
Volcanic Solutions Limited., 20 Moray Place, Dunedin, 9013, New Zealand
ABSTRACT: Diamond-bearing kimberlites in the Fort à la Corne field, east-central Saskatchewan, consist primarily of volcaniclastic deposits which are interstratified with Lower Cretaceous continental, marginal marine and marine sediments. Seventy kimberlite occurrences have been drill-confirmed with the majority of those occurring in the Fort à la Corne main trend. The Star (352 ha) and Orion South (358 ha) kimberlite complexes are located at the south-eastern extremity of the main trend and contain some of the world's best examples of preserved primary volcaniclastic kimberlite deposits. The advanced exploration programs on both the Star and Orion South complexes offer a rare opportunity to examine a wide variety of in situ volcaniclastic kimberlite deposits. Both kimberlite complexes are composed of multiple eruptive units that were deposited episodically over 4 to 6 million years, separated by periods of volcanic quiescence marked by reworking of kimberlite and siliciclastic sedimentation. Detailed logging of core from 100 m spacing grid drilling has revealed well-defined tuff ring, tuff cone, crater and extra crater deposits. Evaluation of these large tonnage, lower grade, coarse diamond size frequency kimberlite complexes requires a methodical and multi-branched exploration strategy utilizing: 1. Grid-pattern core drilling to gain an understanding of the three-dimensional architecture of the kimberlite complexes; 2. Underground bulk sampling to provide appreciable carats for accurate estimates of diamond grade and price; and, 3. Grid-pattern mini-bulk sampling via large diameter drilling to obtain an understanding of the diamond grade across the breadth of each kimberlite. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Crater;  Diamond;  Exploration;  Fort à la Corne;  Tuff cone;  Tuff ring;  Volcanology
DOCUMENT TYPE: Article
SOURCE: Scopus

Verigeanu, D.a , Hetman, C.M.b , Jellicoe, B.a , Baumgartner, M.C.b 
Preliminary geology, mineral chemistry and diamond results from the C29/30 Candle Lake volcanic complex, Saskatchewan, Canada
(2009) Lithos, 112, pp. 529-540. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749091620&partnerID=40&md5=813b8a4d87badf927f97499f89a1b6bf
AFFILIATIONS: Vaaldiam Resources Ltd., 222 Cardinal Crescent, Saskatoon, Sask. S7L 6H8, Canada; 
Mineral Services Canada Inc., 205-930 Harbourside Drive, North Vancouver, BC V7P 3S7, Canada
ABSTRACT: The C29/30 kimberlite is one of two diamondiferous kimberlites in the Candle Lake cluster located in east-central Saskatchewan, Canada, approximately 70 km from the Fort á la Corne kimberlite field. The kimberlites are hosted by a Cretaceous sequence of marine mudstone and shale of the Lower Colorado Group, and underlying siltstone and sandstone of the Mannville Group. This sequence overlies Paleozoic carbonates that were deposited over the Proterozoic crystalline basement. Based on the country rock stratigraphy and morphology of the body, C29/30 is inferred to be Cretaceous in age. The elongated kimberlite body has a lateral extent of approximately 2 km with the long axis oriented in a south-east to north-west direction and an estimated surface expression of 75.3 ha. The investigation of 47 drill cores suggests that this body is a single volcanic complex dominated by a single phase of volcaniclastic kimberlite that is characterised by absent to rare phlogopite within the groundmass of preserved juvenile clasts. Minor amounts of at least one other phase of kimberlite containing conspicuous groundmass phlogopite have also been documented. The subsurface shape of C29/30 is complex and is interpreted to result from a combination of explosive volcanic activity that formed two craters from separate feeder vents. The formation of the elongated trough is poorly understood. It may have formed by a fissure style eruption, or erosive processes related to the mass flow of material away from one of the craters or possible the collapse of an eruption column. The C29/30 kimberlite is similar to bodies of the Fort á la Corne kimberlite field with respect to country rock setting, pipe morphology and the dominant textural varieties present. This contribution presents a preliminary geological model of C29/30 based on data obtained from the drilling programmes completed in 2006, 2007 and 2008. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Diamond;  Geochemistry;  Juvenile clasts;  Kimberlite emplacement;  Petrography;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Kjarsgaard, B.A.a , Harvey, S.b , McClintock, M.c , Zonneveld, J.P.d , Du Plessis, P.b , McNeil, D.e , Heaman, L.d 
Geology of the Orion South kimberlite, Fort à la Corne, Canada
(2009) Lithos, 112, pp. 600-617. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749107509&partnerID=40&md5=636b1ebeb1698da2ff309b8c22714cdb
AFFILIATIONS: Geological Survey of Canada, 601 Booth Street, Ottawa, Ont. K1A 0E8, Canada; 
Shore Gold Inc., 300-224 4th Avenue South, Saskatoon, Sask. S7K 5M5, Canada; 
Volcanic Solutions Ltd., 20 Moray Place, Dunedin, 9016, New Zealand; 
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada; 
Geological Survey of Canada, 3303 33rd Street N.W, Calgary, AB T2L 2A7, Canada
ABSTRACT: A wide variety of primary pyroclastic, volcaniclastic and re-sedimented volcaniclastic deposits derived from multiple kimberlite eruptions are exceptionally well preserved at the Orion South kimberlite body in the Fort à la Corne field in central Saskatchewan. Construction of this kimberlite complex involved episodic kimberlite volcanic events punctuated by periods of volcanic quiescence, erosion and sedimentary deposition within the Western Canadian Sedimentary Basin. The Orion South kimberlite complex erupted into deltaic coastal plain/transitional estuarine (Mannville Group: Cantuar and Pense formations) and shallow marine (Lower Colorado Group: Joli Fou, Viking and Westgate formations) environments. At Orion South, eight distinct kimberlite phases erupted over 6 to 7 million years from ca. 106 Ma (Cantuar Formation equivalent) to ca. 99 Ma (Viking Formation equivalent). Detailed core logging, geochemistry, chronostratigraphy, petrography and geophysics were undertaken to define distinct eruptive phases and reconstruct the depositional environment, volcanic styles and 3-D architecture of the complex. The eight main kimberlite deposits record eruptive styles ranging from magmatic, to 'wet' and 'dry' phreatomagmatic, to submarine eruptions, a consequence of the varying interaction between kimberlite magma and seawater and/or groundwater. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Chronostratigraphy;  Emplacement style;  Kimberlite;  Multiple eruptive events;  Sedimentology;  Volcanology
DOCUMENT TYPE: Article
SOURCE: Scopus

Fitzgerald, C.E.a , Hetman, C.M.b , Lepine, I.a , Skelton, D.S.a , McCandless, T.E.a 
The internal geology and emplacement history of the Renard 2 kimberlite, Superior Province, Quebec, Canada
(2009) Lithos, 112, pp. 513-528. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749115589&partnerID=40&md5=51ce5b15c37f751985a503ee58dc8cad
AFFILIATIONS: Stornoway Diamond Corporation, 116-980 West 1st St, North Vancouver, BC V7P 3N4, Canada; 
Mineral Services Canada, 205-930 Harbourside Dr, North Vancouver, BC V7P 3S7, Canada
ABSTRACT: The Renard 2 kimberlite is located in the Otish Mountains region of Quebec, Canada and is one of the largest pipes in the Renard cluster. The cluster consists of nine kimberlite bodies and was discovered in 2001 by Ashton Mining of Canada Inc. and its joint venture partner SOQUEM Inc. Renard 2 was emplaced into Archean meta-greywacke derived migmatite, gneiss and granite of the Opinaca Subprovince of the eastern Superior Province at approximately 640.5 ± 2.8 Ma. An undetermined amount of erosion has occurred since emplacement with the present surface expression of the pipe estimated to be 0.75 ha. This kimberlite is interpreted as a steep-sided diatreme with minor irregularities in the external shape. The dominant infill is a massive volcaniclastic kimberlite (MVK) that is classified as tuffisitic kimberlite breccia (TKB) and is characterized by a high proportion of granitoid country rock xenoliths. A second dominant infill is a texturally complex, less diluted coherent kimberlite (CK) characterized locally by a transitional textures between CK and TKB. Surrounding the diatreme is a significant zone of variable width comprised of extensively brecciated country rock (+/-kimberlite) and referred to as marginal breccia. In addition to the two main rock types infilling the pipe, a number of hypabyssal kimberlite (HK) dykes and irregular shaped intrusions occur throughout the body, along the pipe contacts, within the marginal breccia and in the surrounding country rock. Geological features displayed by Renard 2 are similar to those described from Class 1 kimberlites of the Kimberley area of South Africa, the Gahcho Kué cluster of Canada and the Pimenta Bueno kimberlite field of Brazil. The economic evaluation of Renard 2 is in progress and to date has included extensive diamond and reverse circulation drilling as well as the collection of an underground bulk sample. Results from material sampled from Renard 2, including a 2449 tonne bulk sample, suggest Renard 2 has an estimated diamond content of 83 cpht (carats per hundred tonnes). A three dimension geology model of the pipe has been developed following the investigation of drill cores, subsurface mapping and petrography combined with diamond studies and geophysics. The model produced is being used to guide and direct the evaluation of the kimberlite and unravel the emplacement history of the pipe. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Diamonds;  Emplacement;  Kimberlite;  Quebec;  Renard 2;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Del Carlo, P.a , Panter, K.S.b , Bassett, K.c , Bracciali, L.d , Di Vincenzo, G.e , Rocchi, S.d 
The upper lithostratigraphic unit of ANDRILL AND-2A core (Southern McMurdo Sound, Antarctica): Local Pleistocene volcanic sources, paleoenvironmental implications and subsidence in the southern Victoria Land Basin
(2009) Global and Planetary Change, 69 (3), pp. 142-161. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71849085747&partnerID=40&md5=f8c65593c31312060255f2548d5b4ebb
AFFILIATIONS: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, via della Faggiola 32, I-56126 Pisa, Italy; 
Department of Geology, Bowling Green State University, Bowling Green, OH 43403, United States; 
Department of Geological Science, University of Canterbury, Private Bag 4800, Christchurch, New Zealand; 
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy; 
Istituto di Geoscienze e Georisorse, CNR, via Moruzzi 1, I-56100 Pisa, Italy
ABSTRACT: We report results from the study of the uppermost 37 m of the Southern McMurdo Sound (SMS) AND-2A drill core, corresponding to the lithostratigraphic unit 1 (LSU 1), the most volcanogenic unit within the core. We present data on the age, composition, volcanological and depositional features of the volcanic sedimentary and tephra deposits of LSU 1 and discuss their source, mechanisms of emplacement and environment of deposition. Sedimentary features and compositional data indicate shallow water sedimentation for the whole of LSU 1. Most of LSU 1 deposits are a mixture of near primary volcanic material with minor exotic clasts derived from the Paleozoic crystalline basement rocks. Among volcanic materials, glassy particles are the most abundant. They were produced by mildly explosive basaltic eruptions occurring in subaerial and subaqueous environments. The Dailey Islands group, 13 km south-southwest of the SMS drill-site, has been identified as a possible source for the volcanics on the basis of similarity in composition and age. 40Ar-39Ar laser step-heating analyses on a lava sample from Juergens Island yields an age of 775 ± 22 ka. Yet because of the minimal reworking features of vitriclasts, preservation of fragile structures in volcaniclastic sediments and evidence for volcanic seamounts to the north of the Dailey Islands, it is likely that some of the material originated also from vents close to the drill-site. Evidence for local volcanic sources and for deposition of sediments in a shallow marine environment provides indications about the local paleogeography and implications for the subsidence history of the southern Victoria Land Basin from Pleistocene to Recent. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: Antarctica;  Erebus Volcanic Province;  paleoenvironment reconstruction;  Victoria Land Basin;  volcaniclastic sediments
DOCUMENT TYPE: Article
SOURCE: Scopus

Galloway, M.a , Nowicki, T.b , van Coller, B.c , Mukodzani, B.c , Siemens, K.a , Hetman, C.b , Webb, K.b , Gurney, J.a 
Constraining kimberlite geology through integration of geophysical, geological and geochemical methods: A case study of the Mothae kimberlite, northern Lesotho
(2009) Lithos, 112, pp. 130-141. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749094890&partnerID=40&md5=83721af2fde8d2043b68e02d1babbe88
AFFILIATIONS: Mineral Services South Africa, PO Box 38668, Pinelands, Cape Town, 7430, South Africa; 
Mineral Services Canada Inc., 205 - 930 Harbourside Drive, North Vancouver, BC V7P 3S7, Canada; 
Remote Exploration Services, PO Box 38668, Pinelands, Cape Town, 7430, South Africa
ABSTRACT: The Cretaceous Mothae kimberlite is located in northern Lesotho on the southeast margin of the Kaapvaal craton. Historical work suggests that Mothae has a low average diamond grade of ~ 3 cpht and the economic viability therefore depends on the presence of large, high quality (and thus value) diamonds as does that of the nearby Letseng Diamond Mine. Defining such a diamond population requires a very large and representative bulk sample. The near surface geology of the Mothae kimberlite was investigated using ground geophysical surveys, pit mapping, petrography, measurements of the mantle components and whole rock compositions. Integration of data from these different approaches clearly defines the outline of the kimberlite at the surface and permits definition, with varying confidence levels, of at least six geologically distinct domains within the body. The domains are defined primarily on the basis of variations in the relative abundances of certain mantle-derived minerals extracted from exploratory pit samples, supported to varying extents by geophysically-defined zones, variations in kimberlite type (established petrographically) and variations in whole rock composition. The domains are interpreted to reflect the presence of multiple phases of volcaniclastic kimberlite each with a potentially different diamond content. The map of the near surface geology constructed on the basis of the work described in this paper provides a valuable framework for planning of further drilling and sampling work aimed at constraining the diamond resource at Mothae. This study illustrates the value of an integrated, multidisciplinary approach to understanding the geology of a complex kimberlite body during the early stages of evaluation. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Diamonds;  Geochemistry;  Geophysics;  Kimberlite evaluation;  Mineralogy;  Petrography
DOCUMENT TYPE: Article
SOURCE: Scopus

Nelson, C.E., Jerram, D.A., Hobbs, R.W.
Flood basalt facies from borehole data: Implications for prospectivity and volcanology in volcanic rifted margins
(2009) Petroleum Geoscience, 15 (4), pp. 313-324. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350378821&partnerID=40&md5=bc63b2833fa88835eee9283149b8d51c
AFFILIATIONS: Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom
ABSTRACT: Flood basalt successions cover many potentially prospective sedimentary basins world-wide, and a few instances exist of intra-basalt petroleum discoveries. However, little is known about the architecture and rock properties of the lava flows, intrusions and other lithologies that make up these successions. We present a simple, effective method of obtaining information from borehole data on the different volcanic facies within a flood basalt succession. Our aims are: (1) to provide a means of determining proportions of different volcanic facies without detailed examination of borehole data or where borehole data are limited; (2) to explore the relationship between onshore and offshore observations. The facies classification scheme providing the framework for this research includes tabularclassic lava flows, compound-braided lava flows, hyaloclastites and intrusions. We show how this scheme can increase our knowledge of the offshore succession and can be useful in hydrocarbon exploration. In the Faroe Islands, three different basalt formations display a range of facies onshore. Boreholes have been drilled through these, and several kilometres' depth of log data collected. The proximity of these boreholes to onshore observations allows the identification of different facies within the wireline log data. This work demonstrates that histograms of P-wave velocities provide an efficient method of identifying the different facies, and we also explore why these distributions are so different. When applied to borehole data from published ODP wells and one commercial well, it is possible to estimate proportions of the different volcanic facies using the velocity distributions alone. © 2009 EAGE/Geological Society of London.
AUTHOR KEYWORDS: Faroe Islands;  Lava flows;  North Atlantic igneous province;  Volcaniclastic;  Wireline logs
DOCUMENT TYPE: Article
SOURCE: Scopus

Kurszlaukis, S.a , Mahotkin, I.b , Rotman, A.Y.c , Kolesnikov, G.V.c , Makovchuk, I.V.c 
Syn- and post-eruptive volcanic processes in the Yubileinaya kimberlite pipe, Yakutia, Russia, and implications for the emplacement of South African-style kimberlite pipes
(2009) Lithos, 112, pp. 579-591. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749107216&partnerID=40&md5=6a1244119245af87cac25c138b904779
AFFILIATIONS: De Beers Canada Inc., 65 Overlea Boulevard, Suite 300, Toronto, Ont. M4H 1P1, Canada; 
De Beers, Moscow, Russian Federation; 
ALROSA, Mirny, Russian Federation
ABSTRACT: The Yubileinaya kimberlite pipe, with a surface area of 59 ha, is one of the largest pipes in the Yakutian kimberlite province. The Devonian pipe was emplaced under structural control into Lower Paleozoic karstic limestone. The pipe complex consists of several smaller precursor pipes which are cut by the large, round Main pipe. While the precursor pipes show many features typical for root zones, Main pipe is younger, cuts into the precursor pipes and exposes well-bedded volcaniclastic sediments. The maximum estimated erosion since emplacement is 250 m. Open pit mapping of a 180 m thick kimberlite sequence documents the waning phases of the volcanic activity in the kimberlite pipe and the onset of its crater infill by resedimentation. Three volcanic lithofacies types can be differentiated. The deepest and oldest facies type is a massive volcaniclastic rock ("AKB") only accessible in drill core. It is equivalent to Tuffisitic Kimberlite in South African pipes and thought to be related to the main volcanic phase which was characterized by violent explosions. The overlying lithofacies type comprises primary and resedimented volcaniclastic sediments as well as rock avalanche deposits sourced from the exposed maar crater collar. It represents the onset of sedimentation onto the crater floor during the waning phase of volcanic eruptions, where primary pyroclastic deposition was contemporaneous with resedimentation from the tephra wall and the widening maar crater. Ongoing volcanic activity is also testified by the presence of a vertical feeder conduit marking the area of the last volcanic eruption clouds piercing through the diatreme. This feeder conduit is overlain by the third and youngest lithofacies type which consists mainly of resedimented volcaniclastic material and lake beds. During the sedimentation of this facies, primary volcanic activity was only minor and finally absent and resedimentation processes dominated the crater infill. The Yubileinaya pipe complex exposes root zones, contact breccias as well as diatreme and crater infill sediments. It has all features typical of large South African-style pipes and much can be learned from Yubileinaya about the emplacement sequence and behaviour of these pipes. Emplacement of the pipe occurred over an extended time span with intermittent phases of volcanic quiescence and consolidation. The AKB reveals little direct evidence of what sort of emplacement process was dominant during the main period of volcanic activity. There is neither textural evidence that violent degassing of a juvenile gas phase has caused pipe excavation, nor that external water was present during the main phase of volcanic eruptions. However, there is clear evidence in rock textures that meteoric surface water was present during crater infill. Base surge deposits forming part of the bedded crater infill sequence indicate that water was present in the eruption clouds and, hence, the root zone of the pipe. There is no reason to assume that groundwater did not also have access to the ascending magma during the main phase of volcanic activity that excavated the pipe and formed the AKB. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Crater;  Emplacement;  Kimberlite;  Phreatomagmatic;  Pipe;  Tuffisitic
DOCUMENT TYPE: Article
SOURCE: Scopus

Mohapatra, B.K., Mishra, P.P., Singh, P.P., Rajeev
Manganese ore deposits in Koira-Noamundi province of Iron Ore Group, north Orissa, India: In the light of geochemical signature
(2009) Chemie der Erde - Geochemistry, 69 (4), pp. 377-394. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749105868&partnerID=40&md5=807a5bffbeb2520368f47e2cc260559a
AFFILIATIONS: Mineralogy Department, Institute of Minerals and Materials Technology, Bhubaneswar, India
ABSTRACT: Several small Mn-Fe oxide and Mn-oxide ore bodies associated with Precambrian Iron Ore Group of rocks are located within Koira-Noamundi province of north Orissa, India. These deposits are classified into in situ (stratiform), remobilized (stratabound) and reworked categories based on their field disposition. Volcaniclastic/terrigenous shale in large geographic extension is associated with these ore bodies. The in situ ore bodies are characterised by cryptomelane-, romanechite- and hematite-dominating minerals, low Mn/Fe ratio (1.1) and relatively lower abundance of trace (1500-2500 ppm) constituents. In such type of deposits the stratigraphic conformity of oxides with the tuffaceous shale suggests precipitation of Mn and Fe at a time of decreased volcaniclastic/terrigenous contribution. The minor and trace elements were removed from solution by adsorption rather than by precipitation. Both Mn and Fe oxides when precipitated adsorb trace elements strongly but the partitioning of elements takes place during diagenesis. The inter-elemental relationship reveals that Cu, Co, Ni, Pb and Zn were adsorbed on precipitating hydrous Mn oxides and form manganates. Some of these elements probably get desorbed from Fe oxide because of their inability to substitute for Fe3+ in the lattice of its oxide. However, P, V, As and Mo were less partitioned and retained in Fe-oxide phase. Positive correlation between Al2O3 and SiO2, MgO, Na2O, TiO2 and some traces like Li, Nb, Sc, Y, Zr, Th and U points to their contribution through volcaniclastic/terrigenous detritus of both mafic and acidic composition. The remobilized ore bodies are developed in a later stage through dissolution, remobilization and reprecipitation of Mn oxides in favorable structural weak planes under supergene environment. Increase in average Mn/Fe ratio (8) and trace content (5000-8500 ppm) by 5-2.5 orders of magnitude, respectively, or more above its abundance in adjoining/underlying protore is characteristic of these deposits. The newly formed Mn ores constituting lithiophorite, cryptomelane/romanechite and goethite get quantitatively enriched in traces like Cu, Co, Ni, Pb and Zn. Positive correlation between Mn, Li, Co and Zn is due to the formation of mineral of lithiophorite-chalcophanite group during redistribution and reconcentration of Mn oxide. P and V, which were present in Fe oxide, also get dissolved and reprecipitate with Fe oxyhydroxide in these ores. Some other elements like Y, Th and U show positive relation with Fe. This is probably due to leaching of these elements during chemical weathering of associated shale and getting re-adsorbed in Fe-oxyhydroxide phase. However, under oxidizing environment selective cations like Ba, K, etc. resorb from Mn-structure, resulting in the development of pyrolusite (Mn/Fe&gt;20). In such transformation, trace metals from pyrolusitic structure expels out, resulting thereby in a considerable reduction in total trace value (&lt;3000 ppm). The reworked ore bodies are allochthonous in nature and developed through a number of stages during terrain evolution and lateritisation. Secondary processes such as reworking of pre-existing crust; solution and remobilization; precipitation and cementation and transport, etc. are responsible for their development. Such deposits are usually very low in Mn/Fe ratio (3) and trace content (&lt;2000 ppm). © 2009 Elsevier GmbH. All rights reserved.
AUTHOR KEYWORDS: Geochemistry;  Iron Ore Group;  Koira-Noamundi province;  Manganese ore
DOCUMENT TYPE: Article
SOURCE: Scopus

Furnes, H.a , Rosing, M.b , Dilek, Y.c , de Wit, M.d 
Isua supracrustal belt (Greenland)-A vestige of a 3.8 Ga suprasubduction zone ophiolite, and the implications for Archean geology
(2009) Lithos, 113 (1-2), pp. 115-132. Cited 10 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350221709&partnerID=40&md5=7038215385e83a1c8021bd9d2fcddfb8
AFFILIATIONS: Department of Earth Science, Centre for Geobiology, University of Bergen, Norway; 
Nordic Centre for Earth Evolution, Geological Museum, Univ. of Copenhagen, Denmark; 
Department of Geology, Miami University, Oxford, OH, United States; 
AEON, Department of Geological Sciences, University of Cape Town, South Africa
ABSTRACT: The mafic-ultramafic units of the ∼ 3.8 Ga Isua supracrustal belt (ISB) in Greenland occur in a two-armed arcuate zone (eastern and western arms) and are grouped into two major tectonostratigraphic units based on their lithological and geochemical characteristics: (1) Undifferentiated amphibolites (UA), and (2) Garbenschiefer amphibolites (GA). The UA contains all major lithological units of a typical Penrose-type complete ophiolite sequence. The GA is composed dominantly of volcaniclastic and volcanic rocks, commonly found in immature island arcs. The available geochemical data from UA and GA show distinct differences between the two units. Compared with the geochemical evolution of some of the well known Phanerozoic ophiolites, the pillow lavas and associated dikes of the UA show a compositional range that is similar to typical MORB-type Ligurian ophiolites in the Western Alps-Apennines and those displayed by LIP-type Caribbean ophiolites. The GA is characterized by island arc tholeiite (IAT) to boninite-like rocks and defines a magmatic evolution that is comparable to that of suprasubduction zone (SSZ) ophiolites in the Mediterranean region. Our proposed geodynamic model for the ISB suggests that the UA was built by primary to differentiated, mantle-generated melts during seafloor spreading, little to moderately affected by subduction processes, and that the IAT to boninitic-like rocks of the GA formed at a later stage by melting from a strongly subduction-affected, depleted and hydrated mantle. Our interpretation of the ISB is that the UA and GA represent early and late stages, respectively, in the formation of a SSZ ophiolite. This implies that Phanerozoic-type plate tectonic processes, such as seafloor spreading and subduction, were operating by 3.8 Ga in the Palaeoarchean. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Archean oceanic crust and tectonics;  Isua supracrustal belt;  Ophiolites;  Suprasubduction zone magmatism
DOCUMENT TYPE: Article
SOURCE: Scopus

Mitchell, S.F.
The cretaceous crinoid uintacrinus socialis from Jamaica and its significance for global correlation
(2009) Geological Magazine, 146 (6), pp. 937-940. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-76449083689&partnerID=40&md5=538a5b97a6725fa842436e4b95c09be5
AFFILIATIONS: Department of Geography and Geology, University of the West Indies, Mona, Kingston 7, Jamaica
ABSTRACT: The late Cretaceous crinoid Uintacrinus socialis Grinnell, which is a potential marker for the base of the Upper Santonian Substage, is reported from the Inoceramus Shales of St Ann's Great River Inlier on the north coast of Jamaica. This is the first record of this species from the Caribbean region and marks its lowest latitudinal distribution reported to date. The Inoceramus Shales are a deep-water clastic mudstone unit which extends the palaeoecological distribution of this crinoid. Uintacrinus socialis proves that the Inoceramus Shales are of Santonian age and will help constrain correlations between the shallow-water platform carbonate/volcaniclastic facies found in the arc successions of the Caribbean and the international chronostratigraphy. © 2009 Cambridge University Press.
AUTHOR KEYWORDS: Cretaceous;  Crinoid;  Jamaica;  Santonian;  Uintacrinus socialis
DOCUMENT TYPE: Article
SOURCE: Scopus

Gernon, T.M.a  b , Fontana, G.c , Field, M.a , Sparks, R.S.J.a , Brown, R.J.a  d , Mac Niocaill, C.c 
Pyroclastic flow deposits from a kimberlite eruption: The Orapa South Crater, Botswana
(2009) Lithos, 112, pp. 566-578. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-71749086855&partnerID=40&md5=e6f118cabad3c736e344f029ee9f3d6d
AFFILIATIONS: Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol, BS8 1RJ, United Kingdom; 
Department of Geology, Trinity College, Dublin, 2, Ireland; 
Department of Earth Sciences, University of Oxford, Oxford, OX1 3PR, United Kingdom; 
Department of Earth and Environmental Sciences, Open University, Milton Keynes, MK7 6AA, United Kingdom
ABSTRACT: The Orapa Diamond Mine (Republic of Botswana) exposes a bi-lobate kimberlite pipe that erupted during the Late-Cretaceous epoch (~ 93 Ma) through Archaean basement and volcano-sedimentary rocks of the Karoo Supergroup. Geological mapping of the crater zone of the South Pipe has revealed a 15-25 m thick in-situ kimberlite pyroclastic flow deposit. The pyroclastic deposit fills in the crater and completely drapes lower units, indicating that the parent flow originated from an adjacent kimberlite pipe. The unit comprises a basal coarse lithic concentration layer exhibiting imbricated clasts, which grades upwards into massive poorly sorted lapilli tuff. The tuff contains abundant sub-vertical degassing structures defined by lithic enrichment and depletion in fine-grained material. Degassing structures commonly emanate from blocks in the basal layer. The presence of degassing structures and a coarse basal layer distinguishes this deposit from pipe-filling massive volcaniclastic kimberlite, which is typically homogeneous in terms of texture and clast size over distances on the order of 100s of metres. Studies of the thermal remanent magnetism in basalt clasts from the deposit, together with serpentine-diopside assemblages, indicate that it was emplaced at elevated temperatures on the order of 200-440 °C, consistent with deposition from a pyroclastic flow. The lithofacies characteristics can be explained by the interaction of the pyroclastic flow with the complex topography of a pre-existing crater. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Crater;  Degassing;  Fluidisation;  Kimberlite;  Orapa;  Pyroclastic flow
DOCUMENT TYPE: Article
SOURCE: Scopus

Ordóñez-Calderón, J.C.a , Polat, A.a , Fryer, B.J.a  b , Appel, P.W.U.c , van Gool, J.A.M.c , Dilek, Y.d , Gagnon, J.E.a  b 
Geochemistry and geodynamic origin of the Mesoarchean Ujarassuit and Ivisaartoq greenstone belts, SW Greenland
(2009) Lithos, 113 (1-2), pp. 133-157. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350214430&partnerID=40&md5=98b2378a357a956c8c37cc4b4d385a73
AFFILIATIONS: Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ont. N9B 3P4, Canada; 
Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ont. N9B 3P4, Canada; 
Geological Survey of Denmark and Greenland, 1350 Copenhagen, Denmark; 
Department of Geology, Miami University, Oxford, OH 45056, United States
ABSTRACT: The Ivisaartoq (ca. 3075 Ma) and Ujarassuit (ca. 3070 Ma) greenstone belts are the largest Mesoarchean supracrustal lithotectonic assemblages in the Nuuk region, SW Greenland. Both greenstone belts underwent polyphase deformation and amphibolite facies metamorphism, and were in due course variously dismembered. Pillow lavas, pillow breccia, magmatic layering, and relic sedimentary structures are well preserved in the Ivisaartoq belt. Volcanic rocks include basalts, and minor andesites and picrites. Boninite-like rocks occur in the Ujarassuit belt. Metasedimentary rocks in the Ujarassuit belt occur as thin layers (0.5-1.0 m) of biotite schists, and in the Ivisaartoq belt as ~ 500 m-thick biotite schists intercalated with minor quartzitic gneisses. There is no field evidence indicating that the Ivisaartoq and Ujarassuit supracrustal rocks were deposited on older continental basement, and their volcanic rocks do not exhibit any geochemical trends indicating contamination by Archean upper continental crust. Four groups of amphibolites (metavolcanic rocks) were recognized in the Ujarassuit greenstone belt on the basis of their REE and HFSE characteristics: (1) Group 1 is characterized by near-flat REE patterns (La/Smcn = 0.77-1.14; La/Ybcn = 0.84-1.24) and moderate negative Nb anomalies (Nb/Nb* = 0.60-0.79); (2) Group 2 displays LREE-depleted patterns (La/Smcn = 0.53-1.02; La/Ybcn = 0.32-0.61) and pronounced negative Nb anomalies (Nb/Nb * = 0.32-0.67); (3) Group 3 consists of LREE depleted patterns (La/Smcn = 0.69-0.84; La/Ybcn = 0.55-0.91) and absence of significant Nb anomalies (Nb/Nb* = 0.92-1.15); and (4) Group 4 has concave-upward REE patterns (La/Smcn = 1.64-2.42, Gd/Ybcn = 0.57-1.01) and large negative Nb anomalies (Nb/Nb * = 0.28-0.42). The depletion of LREE in Group 2 amphibolites appears to have resulted from mobility of these elements during metamorphism. Group 1, 3, and 4 amphibolites retain their near-primary geochemical signatures and their trace element patterns are comparable to those of Phanerozoic oceanic island arc tholeiites (IAT), normal-mid-ocean ridge basalts (N-MORB), and boninites, respectively. The trace element patterns of the least altered meta-ultramafic rocks (La/Ybcn = 2.48-1.35; Nb/Nb* = 0.31-0.60) are comparable to those of modern subduction-related picrites. Amphibolites with an andesitic composition show large negative Nb anomalies (Nb/Nb* = 0.21-0.55), enriched LREE patterns (La/Ybcn = 6.29-15.64), and fractionated HREE (Gd/Ybcn = 2.61-3.12) implying deep melting in equilibrium with residual garnet in the source. Biotite schists and quartzitic gneisses have low chemical indexes of alteration values (CIA = 46 to 62) and trace element characteristics indicating volcaniclastic sedimentary protoliths derived from poorly weathered felsic to mafic source rocks. Collectively, the geochemical features of metavolcanic and metasedimentary rocks suggest that the Ivisaartoq and Ujarassuit greenstone belts represent dismembered fragments of Mesoarchean supra-subduction zone oceanic crust formed in an arc-forearc-backarc tectonic setting. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Amphibolite;  Boninite;  Greenstone belt;  Mesoarchean oceanic crust;  Picrite;  Supra-subduction zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Lokier, S.W.a , Wilson, M.E.J.b , Burton, L.M.c 
Marine biota response to clastic sediment influx: A quantitative approach
(2009) Palaeogeography, Palaeoclimatology, Palaeoecology, 281 (1-2), pp. 25-42. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69949085705&partnerID=40&md5=e4e826df26a4b5dfc514fb7f858d2c73
AFFILIATIONS: Petroleum Geosciences Program, The Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emirates; 
Department of Applied Geology, Curtin University, P.O. Box U1987, Perth, WA 6845, Australia; 
StatoilHydro Petroleum ASA, Postboks 910, NO-9481 Harstad, Norway
ABSTRACT: There have been few quantitative studies of the effects of siliciclastic and volcaniclastic sediment influx on carbonate producing organisms from the geological record. This study presents the results of quantitative field, petrographic and acid digestion analyses of samples from three Cenozoic shallow-water mixed carbonate-volcani/siliciclastic depositional environments-the Miocene Wonosari Formation of south Java, the Miocene Batu Putih Limestone of east Borneo, and the Eocene Collsuspina Limestone of northeast Spain. Carbonate production in these systems is dominated by larger benthic foraminifera, coralline algae and corals. Analyses of the quantity, grainsize and type of volcani/siliciclastic sediment within these mixed successions have allowed assessment of the influence of these factors on shallow-water carbonate producers. Larger benthic foraminifera and coralline algae exhibit the greatest tolerance to siliciclastic sediment influx (abundant up to 55 and 38 wt.%, respectively) at a range of grain sizes (to coarse sand). Platy corals are also present within sediments containing a large proportion of insoluble material (< 80%); however, these are limited to clay-dominated horizons with a maximum siliciclastic size of fine sand grade. Branching and massive corals exhibit the least tolerance to large quantities of insoluble material (usually < 40% up to medium sand, and usually < 25% up to very fine sand, respectively). These variations probably reflect organism: 1) mobility, 2) ability to self clean, 3) morphology and 4) feeding mechanisms relative to: a) sediment settling, b) turbidity, c) abrasion, d) energy, e) water depth, f) light levels, and g) nutrients. The influx of volcaniclastic and siliciclastic grains of comparable size does not appear to have any differential effect on carbonate producers; although corals may be more susceptible to damage by angular volcanic shards. Geologically averaged rates of clastic accumulation and their potential influences on carbonate producers inferred herein may be difficult to compare directly with the daily and seasonal fluctuations experienced by modern clastic influenced systems. However, this study may aid our understanding of the likely effects of increased clastic influx (today commonly anthropogenically related) to marine carbonate environments over longer time periods. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Algae;  Borneo;  Carbonates;  Cenozoic;  Coral;  Java;  Larger benthic foraminifera;  Nutrients;  Sedimentation;  Siliciclastic;  Spain;  Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Aldega, L.a , Cuadros, J.a , Laurora, A.b , Rossi, A.b 
Weathering of phlogopite to beidellite in a karstic environment
(2009) American Journal of Science, 309 (8), pp. 689-710. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-73849105657&partnerID=40&md5=dd61365f627c85e78b4a9f73eb5941ae
AFFILIATIONS: Department of Mineralogy, Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom; 
Dipartimento di Scienze della Terra, Università di Modena e Reggio Emilia, Largo S. Eufemia, 19, 41100 Modena, Italy
ABSTRACT: The extent of natural weathering of phlogopite crystals in a karstic environment and the composition of its weathering products have been examined through a multi-method investigation carried out on a volcanoclastic deposit discovered in the Grotta del Cervo cave, Pietrasecca, central Italy. Phlogopite crystals are a mixture of 1M and 2M1 polytypes and show mixedlayering with a low amount (1-4%) of smectite in the glass groundmass. Phlogopite crystals vary in composition from phlogopite to ferroan phlogopite. Their average structural formula is (K0.92Na0.03Ba 0.03Ca0.02)(Mg2.05Al0.01Fe 2+0.19Fe3+0.40Mn 0.01Ti0.15□0.19)(Si2.63Al 1.37)O10.16(OH1.57F0.27). Micromorphological, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), scanning electron microscopy (SEM), and microprobe analyses (EMPA) showed that the mineralogical evolution of phlogopite crystals is consistent with in-situ pseudomorphic weathering of mica to Al-rich dioctahedral (rather than Mg-rich) clay minerals (beidellite-like) via phlogopite-smectite mixed-layer phases. The main mechanism of transformation is a layer-by-layer modification in which water composition, enriched in Si and Al from glass dissolution, is a major control. Mg loss, Ca and Na exchange for K, enrichment in Si and Al are the main processes required for beidellitization of phlogopite. Glass alteration produced sequentially smectite, chabazite, phillipsite and analcime, as leaching progressed and the interstitial fluids became increasingly alkaline. The type of zeolite found in the several samples (in the chabazite, phillipsite, analcime series) indicates that the alteration extent increases from wall to the ceiling and to the floor of the cave.
DOCUMENT TYPE: Article
SOURCE: Scopus

Rojas Vera, E.A., Folguera, A., Ramos, V.A.
Stratigraphy of the central sector of the Loncopué Trough: The Quaternary depocenter of the Huecú (Western sector of the Neuquén basin) [Estratigrafía del sector central de la fosa de loncopué: El depocentro cuaternario del Huecú sector occidental de la Cuenca Neuquina]
(2009) Revista de la Asociacion Geologica Argentina, 65 (2), pp. 400-412. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955319041&partnerID=40&md5=e3b3a44569a8f30e272da4f0391aeda9
AFFILIATIONS: Laboratorio de Tectónica Andina, FCEyN, Universidad de Buenos Aires - CONICET, Argentina
ABSTRACT: The Huecú depocenter is located in the central sector of the Loncopué trough in western Neuquén. This basin is composed of volcanic, volcaniclastic, fluvial and lacustrine deposits, younger than 1.6 Ma encompassing postglacial and even historical sediments and lavas. During most of its evolution, the Huecú depocenter has constituted a small closed depression (pullapart basin) restricted to the Loncopué trough, a major extensional retroarc basin in the Central and Patagonian Andes. This basin was fed from the north since the beginning of its evolution by a series of big amalgamated post-Pliocene stratovolcanoes located in the Mandolegüe Cordillera. The basin was also filled by fissural lava flows originated in the Agrio caldera located to the east grouped in the Escorial Basalt of 1.6 to 0.8 Ma. Polygenetic volcanic products form in the region big stratovolcanoes among which the Trolón and Colorado volcanic centers were the most prominent. These centers of Pleistocene age were highly eroded by the last glacial activity that affected the region. Nearly at the end of the glacial period two fissural volcanic fields covered the Huecú depocenter corresponding to the Rankül-Lom Basalt and preglacial Tres Hermanos basalts. Finally postglacial volcanic lavas covered most of the Huecú depocenter. These were grouped in the Cerro Artillería Basalts and postglacial Tres Hermanos basalt, which have recurrently dammed the main fluvial basins in the area. The fluvial and lacustrine deposits are represented by El Huecú and Mar Pequeño Formations.
AUTHOR KEYWORDS: Extensional deformation;  Historic floods;  Pull-apart basin;  Retroarc volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Silvestro, J., Atencio, M.
The río Grande and Palauco Cenozoic basin: Age, evolution and structural control, Malargue fold-belt (36°S) [La cuenca cenozoica del río Grande y Palauco: Edad, evolución y control estructural, faja plegada de Malargüe (36°S)]
(2009) Revista de la Asociacion Geologica Argentina, 65 (1), pp. 154-169. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955340705&partnerID=40&md5=57bef0249acdaaf5e539196e03a171ec
AFFILIATIONS: YPF S.A., Buenos Aires, Argentina
ABSTRACT: The Palauco and Rio Grande valley area at 36° south latitude is part of the Malargüe fold-belt in southern Cordillera Principal. The Cenozoic tectonic evolution of this area was recorded by volcaniclastic sediments deposited in syntectonic basins. The structural configuration of basement-involved structures at this latitude, defines an internal part where the Rio Grande sub-basin was developed and a frontal part where Palauco sub-basin was paced. The filling of these basins shows a pre-growth stage dominated by basaltic sequences that was present up to about 23 Ma. From 18 Ma with the uplift of the main structures, each subbasin evolved in an independent way. Therefore, the western part of Rio Grande sub-basin was fed by coarse proximal facies related to the uplift of the Sierra Azul anticline, while the distal fine-sediments and evaporates located in the eastern part of the basin wedged-up against Pampa Paluco-Ranquil Co anticline, showing that this structure was already an internal barrier. This stage finished approximately at 11 Ma, age from which both sub basins show again a similar filling dominated by volcanic deposits present in the whole area. During this new stage, different events of reactivation of the Pampa Palauco-Ranquil Co anticline were recorded by angular unconformities observed in the field, which were constrained at 11 Ma and 8 Ma from radiometric determinations. These events also have generated the development of the new deformation front to the east, with the uplift of the Cerro Fortunoso, Loma Amarilla and Rincón Colorido anticlines, giving the definitive configuration to the basin.
AUTHOR KEYWORDS: Foreland basins;  Growth strata;  Malargüe fold belt;  Radiometric ages;  Sequences
DOCUMENT TYPE: Article
SOURCE: Scopus

Charrier, R., Farías, M., Maksaev, V.
Tectonic, paleogeographic, and metallogenic evolution during the Cenozoic in the Andes of Central and Northern Chile and implication for the adjacent regions of Bolivia and Argentina [Evolución tectónica, paleogeográfica y metalogénica durante el cenozoico en los Andes de Chile Norte y Central e implicaciones para las regiones adyacentes de Bolivia y Argentina]
(2009) Revista de la Asociacion Geologica Argentina, 65 (1), pp. 5-35. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77955319407&partnerID=40&md5=11b0c98134bab5a323b1e63d893460a1
AFFILIATIONS: Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile
ABSTRACT: The Incaic orogeny created significant geographical relief during the Middle Eocene, along most of the area of the preceding magmatic arc, the Incaic Cordillera. This NNE-trending elevated terrain extended from southern Peru to central Chile and formed the boundary between two paleogeographical domains with dissimilar geological evolutions during the rest of the Cenozoic. The western domain was characterized by erosion and sedimentation processes. The eastern domain also included significant erosional episodes, but was characterized by different evolutions north and south of ~27°S. Northward of this latitude, within the Altiplano-Puna realm, the magmatic arc remained in a fixed position, coinciding with the current active arc, and was bordered by a back-arc foreland basin; whereas southward of ~27°S a succession of magmatic arcs developed with a prominent eastward migration. The Late Eocene to Late Oligocene- Early Miocene was characterized by the development of an extensive intra-arc extensional basin, the Abanico Basin. A succession of volcanic and volcaniclastic rocks, with minor sedimentary intercalations, up to 3,000 m thick were deposited within this basin. At about the boundary between the Oligocene and the Miocene a compressive tectonism affected the whole orogen rejuvenating the core of the Incaic Cordillera and resulted in the tectonic inversion of the Abanico Basin; leading to the syntectonic sedimentation on both sides of the new elevated terrain. The beginning of this tectonism is coincident with the Pehuenche orogeny, but the compression extended until the Early Pliocene. During the Early to Middle Miocene the deformation extended to the east with the development of foreland fold and thrust belts and basins. Within the western domain in northern Chile, area of the current Central Depression and Precordillera, the accumulation of thick sedimentary deposits from the western slope of the Incaic Cordillera originated the Tarapacá and Atacama pediments; whereas an extensive peneplanation developed in central Chile. In Late Miocene the prolonged development of the east-verging fold and thrust belts and the generation of overthrusts deep under the Cordillera, which emerged in the Andean front, would have caused the westward tilting of the whole orogen, accompanied by the uplift of the mountain chain and the beginning of its fluvial incision. During the Late Miocene to Early Pliocene a disturbance of the tectonic evolution produced the westward migration of the deformation that coincides in time with the generation of Cu-Mo porphyry mineralization in the area of the former magmatic arc. The compression continued producing uplift of the Cordillera and peneplain surfaces, and rapid exhumation. The shallow seismicity along major faults parallel to the orogen indicates current dextral transcurrent tectonic regime. The economic Cu-Mo porphyry mineralization originated in the latest stages of the magmatic arcs following episodes of crustal thickening, and the location of the mineralizing centers was generally controlled by major faults.
AUTHOR KEYWORDS: Andes;  Cenozoic;  Incaic cordillera;  Incaic orogeny;  Paleogeography;  Tectonics
DOCUMENT TYPE: Article
SOURCE: Scopus

Sharpenok, L.N., Kukharenko, E.A., Kostin, A.E.
New provisions for volcanogenic rocks in the Petrographic Code
(2009) Journal of Volcanology and Seismology, 3 (4), pp. 279-293. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349229433&partnerID=40&md5=2c7ffbe165d3efe1c622baa34eca2743
AFFILIATIONS: Karpinsky All-Russia Geological Research Institute, St. Petersburg 199106, Russian Federation
ABSTRACT: Results are reported from recent developments relating to volcanic rocks; these were necessary in connection with an analysis of remarks and proposals for the 1995 Petrographic Code, as well as resulting from an analysis of practical applications of this document. The new materials are concerned with three directions: (1) further specification of the "total alkali-silica" diagram (TAS) for acidic rocks and trachytes; (2) improving the classification of clastic volcanogenic rocks and regulating the volcaniclastic terminology; and (3) substantiating the principles for subdividing sedimentary-and-volcanogenic rocks into subunits of different hierarchical levels and specifying the associated criteria. The insertion of results of these developments into a second, revised and supplemented edition of the Petrographic Code and their application to geological studies will enhance the quality of the latter. © Pleiades Publishing, Ltd. 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Balini, M.a , Nicora, A.a , Berra, F.a , Garzanti, E.b , Levera, M.a , Mattei, M.c , Muttoni, G.a , Zanchi, A.b , Bollati, I.a , Larghi, C.a , Zanchetta, S.a , Salamati, R.d , Mossavvari, F.d 
The Triassic stratigraphic succession of Nakhlak (central Iran) a record from an active margin
(2009) Geological Society Special Publication, (312), pp. 287-321. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349173966&partnerID=40&md5=1397bb17177df9bab94a5ddc1b982976
AFFILIATIONS: Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy; 
Dipartimento di Scienze Geologiche e Geotecnologie, Università di Milano-Bicocca, Piazza della Scienza 4, Milano 20126, Italy; 
Dipartimento di Scienze Geologiche, Università Roma TRE, Largo San Leonardo Murialdo 1, 00146 Roma, Italy; 
Geological Survey of Iran, Azadi Square, Meraj Avenue, 13185-1494 Tehran, Iran
ABSTRACT: An important, 2.4 km-thick Triassic succession is exposed at Nakhlak (central Iran). This succession was deformed during the Cimmerian orogeny and truncated by an angular unconformity with undeformed Upper Cretaceous sediments. This integrated stratigraphic study of the Triassic included bed-by-bed sampling for ammonoids, conodonts and bivalves, as well as limestone and sandstone petrographic analyses. The Nakhlak Group succession consists of three formations: Alam (Olenekian-Anisian), Bāqoroq (?Upper Anisian-Ladinian) and Ashin (Upper Ladinian). The Alam Formation records several shifts from carbonate to siliciclastic deposition, the Bāqoroq Formation consists of continental conglomerates and the Ashin Formation documents the transition to deep-sea turbiditic sedimentation. Petrographic composition has been studied for sandstones and conglomerates. Provenance analysis for Alam and most of the Ashin samples suggests a volcanic arc setting, whereas the samples from the Bāqoroq Formation are related to exhumation of a metamorphic basement. The provenance data, together with the great thickness, the sudden change of facies, the abundance of volcaniclastic supply, the relatively common occurrence of tuffitic layers and the orogenic calc-alkaline affinity of the volcanism, point to sedimentation along an active margin in a forearc setting. A comparison between the Triassic of Nakhlak and the Triassic succession exposed in the erosional window of Aghdarband (Koppeh Dag, NE Iran) indicates that both were deposited along active margins. However, they do not show the same type of evolution. Nakhlak and Aghdarband have quite different ammonoid faunal affinities during the Early Triassic, but similar faunal composition from the Bithynian to Late Ladinian. These results argue against the location of Nakhlak close to Aghdarband. © The Geological Society of London 2009.
DOCUMENT TYPE: Article
SOURCE: Scopus

Romagnoli, C.a , Kokelaar, P.b , Casalbore, D.a , Chiocci, F.L.c  d 
Lateral collapses and active sedimentary processes on the northwestern flank of Stromboli volcano, Italy
(2009) Marine Geology, 265 (3-4), pp. 101-119. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69249222554&partnerID=40&md5=762848745b4ed6dc362022a792c1fc38
AFFILIATIONS: University of Bologna, Dip. Scienze della Terra e Geologico-Ambientali, P.zza di Porta S.Donato 1, 40126 Bologna, Italy; 
Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX, United Kingdom; 
University of Roma La Sapienza, Dip. Scienze della Terra, P.le Aldo Moro 5, Roma, 00185, Italy; 
CNR, Istituto di Geologia Applicata e Geoingegneria, Roma, P.le Aldo Moro 5, Roma 00185, Italy
ABSTRACT: The marine volcaniclastic system extending to 3 km water depth on the northwest flank of Stromboli volcano has been surveyed using seismo-acoustic profiling, multibeam bathymetry, deep-towed long-range side-scan sonar imaging and box-core sampling. Deposits and sea-floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present Sciara del Fuoco scar. An extensive (170 km2) debris-avalanche deposit characterized by subdued hummocks (megablocks) is buried by turbidites formed from gravity currents that originated in Sciara del Fuoco. The currents were mainly deflected along the margin of the avalanche deposit, but also spilt over onto it. The turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows. The estimated volume of the entire fan-shaped bulge amounts to 12 ± 2.5 km3, about 3.5 km3 of which is attributed to the post-collapse sedimentation. The remaining 8.5 ± 2.5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the NW Stromboli flank. Two units are identified in the distal part of the bulge, through the recognition of their fronts, and these indicate a layered structure for successive debris-avalanche deposits. Granulometric and particle-type characterization of seabed samples shows clast population evolution with sedimentary transport distance, from the main entrance point of debris in Sciara del Fuoco, to the confluence with the Stromboli Canyon, and into the Marsili Basin some 45 km from the island. Changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main Stromboli Canyon from the continental shelf. Abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse-grained material along the channel to the Marsili Basin indicates that a considerable volume of volcaniclastic material from Stromboli lies in the sedimentary succession accumulating on the distal basin floor, where a deep-sea fan is growing. © 2009 Elsevier B.V.
AUTHOR KEYWORDS: density current;  island volcano;  marine geophysical survey;  mass movement;  Stromboli;  volcaniclastic particle analysis
DOCUMENT TYPE: Article
SOURCE: Scopus

Woodcock, D.a , Meyer, H.b , Dunbar, N.c , McIntosh, W.c , Prado, I.d , Morales, G.d 
Geologic and taphonomic context of El Bosque Petrificado Piedra Chamana (Cajamarca, Peru)
(2009) Bulletin of the Geological Society of America, 121 (7-8), pp. 1172-1178. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69949088338&partnerID=40&md5=fdb703799a0f9e07ef605778a4bf74d6
AFFILIATIONS: Marsh Institute of Clark University, 950 Main Street, Worcester, MA 01610, United States; 
U.S. National Park Service, Florissant Fossil Beds National Monument, P.O. Box 185, Florissant, CO 80816, United States; 
New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States; 
Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Av. Arenales 1256, Lima 14, Peru
ABSTRACT: Volcanic and volcaniclastic rocks in the northern Peruvian Andes (central Cajamarca, 79°10′ W, 6°35′ S) contain a diverse assemblage of permineralized woods known as El Bosque Petrificado Piedra Chamana. The fossil forest and associated paleosol are preserved in ash-fall and lahar deposits of the Huambos Formation. Dating of plagioclase from the ash-fall deposit using 40Ar/39Ar methods yields a middle Eocene age of 39.35 ±0.21 Ma. Accuracy of this age determination is supported by a more robust sanidine age of 39.52 ± 0.11 Ma from an underlying welded ignimbrite. Fossil wood and leaves associated with the ash-fall deposit include vertical trees rooted in the paleosol and buried in situ by the ash. Fossil wood is also present in high abundance and diversity in the overlying lahar. The fossils are significant as a low-latitude assemblage including a diversity of both monocots and dicots and in having fossil leaves occurring in close proximity to fossil woods. Preliminary analyses of wood and leaf characters suggest a megathermal climate with some limitations on plant growth associated with limited (seasonal) moisture availability. The assemblage represents lowland tropical forest that was probably growing near sea level and subsequently uplifted to the current elevation at the site (∼2400-2600 m). © 2009 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Edwards, B.R.a , Skilling, I.P.b , Cameron, B.c , Haynes, C.a , Lloyd, A.a , Hungerford, J.H.D.b 
Evolution of an englacial volcanic ridge: Pillow Ridge tindar, Mount Edziza volcanic complex, NCVP, British Columbia, Canada
(2009) Journal of Volcanology and Geothermal Research, 185 (4), pp. 251-275. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68349150651&partnerID=40&md5=b51dea85dd3730c4271eaa96038a69c9
AFFILIATIONS: Department of Geology, Dickinson College, 5 N. Orange Street, Carlisle, PA 17013, United States; 
Department of Geology and Planetary Science, University of Pittsburgh, 200 SRCC Building, Pittsburgh, PA 15260, United States; 
Department of Geology, University of Wisconsin-Milkwaukee, WI, United States
ABSTRACT: Glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice-sheets, and for testing hypotheses about inferred terrestrial ice volumes based on the marine record. Deposits formed by the coincidence of volcanism and ice at the Mount Edziza volcanic complex (MEVC) in northern British Columbia, Canada, preserve an important record for documenting local and possibly regional ice dynamics. Pillow Ridge, located at the northwestern end of the MEVC, formed by ice-confined, fissure-fed eruptions. It comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition, with subordinate finer-grained volcaniclastic deposits and dykes. The ridge is presently ∼ 4 km long, ∼ 1000 m in maximum width, and ∼ 600 m high. Fifteen syn- and post-eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge. We recognize five lithofacies associations: (1) poorly sorted tuff breccia and dykes, (2) proximal pillow lava, dykes and tuff breccia, (3) distal pillow lava, poorly sorted conglomerate and well-sorted volcanic sandstone, (4) interbedded tuff, lapilli tuff, and tuff breccia units, and (5) heterolithic volcanogenic conglomerate and sandstone. Given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water, we agree with Souther [Souther, J.G., 1992. The late Cenozoic Mount Edziza volcanic complex. Geol. Soc. Can. Mem., vol. 420. 320 pp] that the bulk of the edifice formed while confined by ice, but have found evidence for a more complex and variable eruption history than that which he proposed. Preliminary estimates of water-ice depths derived from FTIR analyses of H2O give ranges of 300 to 680 m assuming 0 ppm CO2, and 857 to 1297 m assuming 25 ppm CO2. Variations in depth estimates among samples may indicate that water/ice depths changed during the evolution of the ridge, which is consistent with our interpretations for the origins of different lithofacies associations. Given that the age of the units are likely to be ca. 0.9 Ma [Souther, J.G., 1992. The late Cenozoic Mount Edziza volcanic complex. Geol. Soc. Can. Mem., vol. 420. 320 pp], Pillow Ridge may be the best documentation of a regional high stand of the Cordilleran Ice Sheet (CIS) in the middle Pleistocene, and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: glaciovolcanism;  Mount Edziza volcanic complex;  pillow lava;  tindar;  volcano-ice interaction
DOCUMENT TYPE: Article
SOURCE: Scopus

Tucker, D.S., Scott, K.M.
Structures and facies associated with the flow of subaerial basaltic lava into a deep freshwater lake: The Sulphur Creek lava flow, North Cascades, Washington
(2009) Journal of Volcanology and Geothermal Research, 185 (4), pp. 311-322. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68349155555&partnerID=40&md5=e8a28feb697f7429f8469e52b87c3000
AFFILIATIONS: Geology Department, Western Washington University, 516 High St, Bellingham, WA 98225, United States
ABSTRACT: The ca. 8800 14C yrs BP Sulphur Creek lava flowed eastward 12 km from the Schriebers Meadow cinder cone into the Baker River valley, on the southeast flank of Mount Baker volcano. The compositionally-zoned basaltic to basaltic andesite lava entered, crossed and partially filled the 2-km-wide and &gt; 100-m-deep early Holocene remnant of Glacial Lake Baker. The valley is now submerged beneath a reservoir, but seasonal drawdown permits study of the distal entrant lava. As a lava volume that may have been as much as 180 × 106 m3 entered the lake, the flow invaded the lacustrine sequence and extended to the opposite (east) side of the drowned Baker River valley. The volume and mobility of the lava can be attributed to a high flux rate, a prolonged eruption, or both. Basalt exposed below the former level of the remnant glacial lake is glassy or microcrystalline and sparsely vesicular, with pervasive hackly or blocky fractures. Together with pseudopillow fractures, these features reflect fracturing normal to penetrative thermal fronts and quenching by water. A fine-grained hyaloclastite facies was probably formed during quench fragmentation or isolated magma-water explosions. Although the structures closely resemble those developed in lava-ice contact environments, establishing the depositional environment for lava exhibiting similar intense fracturing should be confirmed by geologic evidence rather than by internal structure alone. The lava also invaded the lacustrine sequence, forming varieties of peperite, including sills that are conformable within the invaded strata and resemble volcaniclastic breccias. The peperite is generally fragmental and clast- or matrix-supported; fine-grained and rounded fluidal margins occur locally. The lava formed a thickened subaqueous plug that, as the lake drained in the mid-Holocene, was exposed to erosion. The Baker River then cut a 52-m-deep gorge through the shattered, highly erodible basalt. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: lava fractures;  Mount Baker;  peperite;  subaqueous lava;  volcano-water interaction
DOCUMENT TYPE: Article
SOURCE: Scopus

Skilling, I.P.
Subglacial to emergent basaltic volcanism at Hlö{eth}ufell, south-west Iceland: A history of ice-confinement
(2009) Journal of Volcanology and Geothermal Research, 185 (4), pp. 276-289. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68349160829&partnerID=40&md5=ed3b241408cdb35e07ec5c8ffcacdd65
AFFILIATIONS: Department of Geology and Planetary Science, University of Pittsburgh, 200 SRCC Building, PA 15260, United States
ABSTRACT: Hlö{eth}ufell is a familiar 1186 m high landmark, located about 80 km northeast of Reykjavík, and 9 km south of the Langkjökull ice-cap in south-west Iceland. This is the first detailed study of this well-exposed and easily accessible subglacial to emergent basaltic volcano. Eight coherent and eleven volcaniclastic lithofacies are described and interpreted, and its evolution subdivided into four growth stages (I-IV) on the basis of facies architecture. Vents for stages I, II, and IV lie along the same fissure zone, which trends parallel to the dominant NNE-SSW volcano-tectonic axis of the Western Volcanic Zone in this part of Iceland, but the stage III vent lies to the north, and is probably responsible for the present N-S elongation of the volcano. The basal stage (I) is dominated by subglacially erupted lava mounds and ridges, which are of 240 m maximum thickness, were fed from short fissures and locally display lava tubes. Some of the stage I lavas preserve laterally extensive flat to bulbous, steep, glassy surfaces that are interpreted to have formed by direct contact with surrounding ice, and are termed ice-contact lava confinement surfaces. These surfaces preserve several distinctive structures, such as lava shelves, pillows that have one flat surface and mini-pillow (< 10 cm across) breakouts, which are interpreted to have formed by the interplay of lava chilling and confinement against ice, ice melting and ice fracture. The ice-contact lava confinement surfaces are also associated with zones of distinctive open cavities in the lavas that range from about 1 m to several metres across. The cavities are interpreted as having arisen by lava engulfing blocks of ice, that had become trapped in a narrow zone of meltwater between the lava and the surrounding ice, and are termed ice-block meltout cavities. The same areas of the lavas also display included and sometimes clearly rotated blocks of massive to planar to cross-stratified hyaloclastite lapilli tuffs and tuff-breccias, termed hyaloclastite inclusions, which are interpreted as engulfed blocks of hyaloclastite/pillow breccia carapace and talus, or their equivalents reworked by meltwater. Some of the stage I lavas are mantled at the southern end of the mountain by up to 35 m thickness of well-bedded vitric lapilli tuffs (stage II), of phreatomagmatic origin, which were erupted from a now dissected cone, preserved in this area. The tephra was deposited dominantly by subaqueous sediment gravity flows (density currents) in an ice-bound lake (or less likely a sub-ice water vault), and was also transported to the south by sub-ice meltwater traction currents. This cone is onlapped by a subaerial pahoehoe lava-fed delta sequence, formed during stage III, and which was most likely fed from a now buried vent(s), located somewhere in the north-central part of the mountain. A 150 m rise in lake level submerged the capping lavas, and was associated with progradation of a new pahoehoe lava-fed delta sequence, produced during stage IV, and which was fed from the present summit cone vent. The water level rise and onset of stage IV eruptions were not associated with any obviously exposed phreatomagmatic deposits, but they are most likely buried beneath stage IV delta deposits. Stage IV lava-fed deltas display steep benches, which do not appear to be due to syn- or post-depositional mass wasting, but were probably generated during later erosion by ice. The possibility that they are due to shorter progradation distances than the underlying stage III deltas, due to ice-confinement or lower volumes of supplied lava is also considered. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Glaciovolcanism;  ice-contact;  lava-fed deltas;  Phreatomagmatism;  subglacial;  Surtseyan;  tuya
DOCUMENT TYPE: Article
SOURCE: Scopus

Homoky, W.B.a , Severmann, S.b , Mills, R.A.a , Statham, P.J.a , Fones, G.R.c 
Pore-fluid Fe isotopes reflect the extent of benthic Fe redox recycling: Evidence from continental shelf and deep-sea sediments
(2009) Geology, 37 (8), pp. 751-754. Cited 11 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69649084742&partnerID=40&md5=25f770ff22879dcd6036d661d0a2d54e
AFFILIATIONS: National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, United Kingdom; 
Department of Earth and Planetary Sciences, Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, United States; 
School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth PO1 3QL, United Kingdom
ABSTRACT: Pore-fluid Fe isotopes may be a unique tracer of sediment respiration by dissimilatory Fe-reducing bacteria, but to date, pore-fluid Fe isotope measurements have been restricted to continental shelf settings. Here, we present δ56Fe values of pore fluids from two distinct sedimentary settings: (1) a riverine-dominated site on the northern California margin (Eel River shelf; 120 m water depth) and (2) biogenic opal-rich volcaniclastic deep-sea sediments from the Southern Ocean (north and south of the Crozet Plateau; 3000-4000 m water depth). The Fe isotope compositions of Crozet region pore fluids are significantly less fractionated (δ56Fe = +0.12‰ to -0.01‰) than the Eel River shelf (δ56Fe = -0.65‰ to -3.40‰) and previous studies of pore-fluid Fe isotopes, relative to average igneous rocks. Our data represent the first measurements of Fe isotope compositions in pore fluids from deep-sea sediments. A comparison of pore-fluid δ56Fe with the relative abundance of highly labile Fe in the reactive sedimentary Fe pool demonstrates that the composition of Fe isotopes in the pore fluids refl ects the different extent of sedimentary Fe redox recycling between these sites. © 2009 Geological Society of America.
DOCUMENT TYPE: Article
SOURCE: Scopus

Idrus, A.a , Kolb, J.b , Meyer, F.M.b , Arif, J.c , Setyandhaka, D.c , Kepli, S.c 
A preliminary study on skarn-related calc-silicate rocks associated with the Batu Hijau Porphyry copper-gold deposit, Sumbawa Island, Indonesia
(2009) Resource Geology, 59 (3), pp. 295-306. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69449083487&partnerID=40&md5=0f0d81ef406ffbd0eab1f00650776dfb
AFFILIATIONS: Department of Geological Engineering, Gadjah Mada University, Jl. Grafika 2, Bulaksumur 55281 Yogyakarta, Indonesia; 
Institute of Mineralogy and Economic Geology, RWTH Aachen University, Aachen, Germany; 
Mine Geology Department, PT Newmont Nusa Tenggara, Batu Hijau Project, Sumbawa, Indonesia
ABSTRACT: Batu Hijau is a world-class gold-rich porphyry copper deposit, situated in Sumbawa Island, Indonesia. Deep drilling indicates that several intervals of calc-silicate rock were intersected, where they are apparently interbedded with volcaniclastic rocks. The calc-silicate rocks occur at the contact with copper-gold-bearing tonalite porphyries. The rocks are fine-grained and granular with green, reddish-brown and white layers. The green layers consist mostly of fine-grained clinopyroxene (diopside and hedenbergite) and the reddish-brown layers consist mostly of garnet (andradite), whereas the white layers are commonly composed of calcite and zeolite (chabazite). The calc-silicate rocks were formed by contact metasomatism of andesitic volcaniclastic rocks, as it is calcic in composition. Paragenesis study reveals at least two stages of calc-silicate mineralization. Stage 1 (prograde) is characterized by the presence of garnet (andradite), clinopyroxene (diopside and hedenbergite), anorthite and quartz at 340-360C (high salinity 35-45 NaCl wt percentage eqn.). Stage 2 (retrograde) is characterized by chlorite and rare epidote at 280-300C (low salinity 1-10 NaCl wt% eqn.). Late calcite ± quartz veinlets and calcite + chabazite veins/veinlets may also be related to this stage and cross cut the oldest mineral assemblages. Mineralization (magnetite, chalcopyrite and pyrite) may occur during the retrograde stage. Clinopyroxene and garnet were modified by Fe-rich hydrothermal fluid (oxidizing condition) indicated by increase of Fe from core to rim of both the cogenetic minerals. The presence of the calc-silicate rocks associated with massive magnetite-chalcopyrite-pyrite assemblage indicates the occurrence of calcic-exoskarn surrounding the Batu Hijau porphyry copper-gold deposit. © Journal compilation © 2009 The Society of Resource Geology.
AUTHOR KEYWORDS: Batu Hijau porphyry Cu-Au deposit;  Calc-silicate;  Indonesia;  Skarn;  Sumbawa
DOCUMENT TYPE: Article
SOURCE: Scopus

Daesslé, L.W.a  b , Rendón-Márquez, G.c , Camacho-Ibar, V.F.a , Gutiérrez-Galindo, E.A.a , Shumilin, E.d , Ortiz-Campos, E.a 
Geochemistry of modern sediments from san quintín coastal lagoon, Baja California: Implication for provenance [Composición geoquímica de sedimentos modernos de la laguna costera de San Quintín, Baja California: implicaciones para la proveniencia]
(2009) Revista Mexicana de Ciencias Geologicas, 26 (1), pp. 117-132. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69349089381&partnerID=40&md5=6e31b0ed15fbe1f685fd0f8e886137bf
AFFILIATIONS: Universidad Autónoma de Baja California (UABC), Instituto de Investigaciones Oceanológicas, Carretera Tijuana-Ensenada Km. 107, 22830 Ensenada, Baja California, Mexico; 
Friedrich Alexander Universität Erlangen-Nürnberg FAU, Institut für Geologie und Mineralogie, Lehrstuhl für Angewandte Geologie, Schloßgarten 5, 91054 Erlangen, Germany; 
Centro de Investigación Científica y Educación, Superior de Ensenada (CICESE), Departamento de Geología, Carretera Tijuana-Ensenada Km. 107, 22830 Ensenada, Baja California, Mexico; 
Instituto Politécnico Nacional-Centro, Interdisciplinario de Ciencias Marinas (IPN-CICIMAR), Departamento de Oceanología, Av. IPN. S/N, Col. Playa Palo de Santa Rita, Apdo. Postal 592, 23096 La Paz, Baja California Sur, Mexico
ABSTRACT: A detailed regional grid of 97 surficial sediment samples is studied for the San Quintín coastal lagoon, which is a shallow embayment located adjacent to a "regionally-rare" intraplate-type basaltic terrain known as San Quintín volcanic field. The influence that this unique lithology and other potential sources have on the recent sediment geochemistry is discussed on the basis of geochemical, petrographic and sedimentological results. The sandy silts and silts in the lagoon are enriched in ferromagnesian minerals such as pyroxenes and hornblende, which form up to 6 and 22%, respectively, of the total mineral count in the sand fraction. These relatively immature feldspathic sediments are characterized by the presence of abundant angular plagioclase (25-60%) and absence of lithics. The La-Sc-Th and Cr-Sc-Th discrimination diagrams suggest that mafic ferromagnesian minerals have a significant effect on the geochemical variance of the sediments. The Cr/Th (median=28) and Co/Th (median=59) ratios are similar to those reported for sands derived from basic rocks. A mafic provenance is probably responsible for the statistical association of Fe, Hf, U, Th, Sc, Cr, Ca, Na and the rare earth elements. An association of Fe, organic carbon and total P with the trace elements Sb, Cr, Br, As, Na, Sc and Co indicates that their distribution is mainly controlled by the presence of Fe-rich minerals, such as hornblende, and organic matter throughout Bahía San Quintín and the northernmost Bahía Falsa, beneath aquaculture racks. Low enrichment factors (<1) for Cr, Sb, As and P indicate that anthropogenic contaminant sources derived from agrochemicals are not significant.
AUTHOR KEYWORDS: Coastal lagoon;  Geochemistry;  Heavy minerals;  Mexico;  Phosphorus;  San quintín;  Sediment;  Volcaniclastic
DOCUMENT TYPE: Article
SOURCE: Scopus

Boldini, D.a , Wang, F.b , Sassa, K.c , Tommasi, P.d 
Application of large-scale ring shear tests to the analysis of tsunamigenic landslides at the Stromboli volcano, Italy
(2009) Landslides, 6 (3), pp. 231-240. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349487724&partnerID=40&md5=f10a214b7c978603ce5ac742611f229b
AFFILIATIONS: Department of Chemical, Mining and Environmental Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy; 
Research Centre on Landslides, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan; 
International Consortium on Landslides, Gokasho, Uji, Kyoto 611-0011, Japan; 
Institute for Geo-Engineering and Environmental Geology, National Research Council, c/o Faculty of Engineering, via Eudossiana 18, 00184 Rome, Italy
ABSTRACT: The island of Stromboli (Southern Italy) is a 4,000-m-high volcanic edifice about 900 m above sea level. Most of the NW flank is formed by a wide scar (Sciara del Fuoco) filled by irregular alternations of volcaniclastic layers and thin lava flows. Between 29 and 30 December 2002, a submarine and a subaerial landslide involved the northernmost part of the Sciara del Fuoco slope and caused two tsunami waves with a maximum run-up of 10 m. Mechanisms of the rapid submarine landslide and the preceding deformation of the subaerial and submarine slope were investigated using large-scale ring shear tests on the saturated and dry volcaniclastic material. The shear behaviour of the material under different drainage conditions was analysed during tests conducted at DPRI, Kyoto University. Pore pressure generation, mobilised shear strength and grain crushing, within a range of displacements encompassing the different stages of evolution of the slope, were considered. Experimental results suggest that even at larger displacements, shear strength of the dry material explains the virtual stability of the slope. Conversely, full or partial liquefaction can be invoked to explain the submarine failure and the subsequent long runout (more than 1,000 m) of the failed materials. © Springer-Verlag 2009.
AUTHOR KEYWORDS: Grain crushing;  Laboratory tests;  Landslide;  Liquefaction;  Shear strength;  Volcaniclastic soil
DOCUMENT TYPE: Article
SOURCE: Scopus

Egger, A.E.a , Colgan, J.P.b , York, C.a 
Provenance and palaeogeographic implications of Eocene-Oligocene sedimentary rocks in the northwestern Basin and Range
(2009) International Geology Review, 51 (9-11), pp. 900-919. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-76449119431&partnerID=40&md5=9976b5520a8c32ceb6e8b3462c789f58
AFFILIATIONS: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, United States; 
US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
ABSTRACT: A thick sequence of uppermost Eocene to lower Oligocene volcaniclastic and sedimentary rocks is exposed at the base of the Warner Range in northeastern California. This isolated exposure provides insight into the palaeogeographic setting of the northwestern Basin and Range during this time period. Significant thinning of the unit over 35km of lateral exposure and predominantly volcanic clast compositions suggest that the sequence was deposited in an alluvial plain adjacent to a volcanic arc. Palaeocurrent indicators in the conglomerates define a NNE transport direction. Detrital zircon analysis on coarse sandstones and dating of individual granite cobbles show a range of ages consistent with a local, volcanic source area primarily from the SSW with some far-travelled input from northern Nevada; the far-travelled component increases in influence as the unit thins to the north. Comparison with other sedimentary sequences of Eocene age and integration with palaeofloral and geophysical data help to define drainage divides, and suggest that this sequence accumulated in a relatively isolated, intra-arc basin. This localized accumulation differs markedly from contemporaneous drainages to the south that transported material westwards from central Nevada to the palaeoshoreline, and suggests that ongoing volcanism had a strong influence on palaeogeography in this region during the Eocene and Oligocene.
AUTHOR KEYWORDS: Basin and Range;  Detrital zircon geochronology;  Oligocene palaeogeography;  Steamboat Formation;  Volcaniclastic sandstone;  Warner Range
DOCUMENT TYPE: Article
SOURCE: Scopus

Boswell, R.a , Shelander, D.b , Lee, M.c , Latham, T.d , Collett, T.c , Guerin, G.e , Moridis, G.f , Reagan, M.f , Goldberg, D.e 
Occurrence of gas hydrate in Oligocene Frio sand: Alaminos Canyon Block 818: Northern Gulf of Mexico
(2009) Marine and Petroleum Geology, 26 (8), pp. 1499-1512. Cited 10 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67650251993&partnerID=40&md5=9710da4cbaab0d50c8b5982bd6bf74ee
AFFILIATIONS: U.S. Department of Energy, National Energy Technology Laboratory, 3610 Collins Ferry Road, Morgantown, WV 26507, United States; 
Schlumberger Reservoir Seismic Services, Houston, TX, United States; 
U.S. Geological Survey, Denver, CO, United States; 
Chevron North America Exploration and Production Company, Houston, TX, United States; 
Lamont-Doherty Earth Observatory, Columbia University, New York, NY, United States; 
Lawrence Berkeley National Laboratory, Berkeley, CA, United States
ABSTRACT: A unique set of high-quality downhole shallow subsurface well log data combined with industry standard 3D seismic data from the Alaminos Canyon area has enabled the first detailed description of a concentrated gas hydrate accumulation within sand in the Gulf of Mexico. The gas hydrate occurs within very fine grained, immature volcaniclastic sands of the Oligocene Frio sand. Analysis of well data acquired from the Alaminos Canyon Block 818 #1 ("Tigershark") well shows a total gas hydrate occurrence 13 m thick, with inferred gas hydrate saturation as high as 80% of sediment pore space. Average porosity in the reservoir is estimated from log data at approximately 42%. Permeability in the absence of gas hydrates, as revealed from the analysis of core samples retrieved from the well, ranges from 600 to 1500 millidarcies. The 3-D seismic data reveals a strong reflector consistent with significant increase in acoustic velocities that correlates with the top of the gas-hydrate-bearing sand. This reflector extends across an area of approximately 0.8 km2 and delineates the minimal probable extent of the gas hydrate accumulation. The base of the inferred gas-hydrate zone also correlates well with a very strong seismic reflector that indicates transition into units of significantly reduced acoustic velocity. Seismic inversion analyses indicate uniformly high gas-hydrate saturations throughout the region where the Frio sand exists within the gas hydrate stability zone. Numerical modeling of the potential production of natural gas from the interpreted accumulation indicates serious challenges for depressurization-based production in settings with strong potential pressure support from extensive underlying aquifers.
AUTHOR KEYWORDS: Alaminos Canyon;  Frio sand;  Gas hydrate;  Gulf of Mexico
DOCUMENT TYPE: Article
SOURCE: Scopus

Gorny, C.a , Busby, C.a , Pluhar, C.J.b , Hagan, J.a , Putirka, K.b 
An in-depth look at distal Sierra Nevada palaeochannel fill: Drill cores through the Table Mountain Latite near Knights Ferry
(2009) International Geology Review, 51 (9-11), pp. 824-842. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-76449086946&partnerID=40&md5=5fa237e390bc0c34d6a821724ef7ad44
AFFILIATIONS: Department of Earth Science, University of California, Santa Barbara, CA 93101, United States; 
Department of Earth and Environmental Sciences, California State University, Fresno, CA 93740, United States
ABSTRACT: The ∼10.4Ma Table Mountain Latite (TML) consists of high-K trachyandesite lavas that likely erupted from the Little Walker Center near Sonora Pass and flowed 80miles (130km) through the palaeo-Stanislaus river channel to Knights Ferry in the Sierra Nevada foothills. Complete sections through the proximal facies of the flow stratigraphy are common in the high-Sierra and along range-front faults, but in much of its distal facies in the Sierra Nevada foothills, the internal features of the unit are poorly exposed. Condor Earth Technologies offered us the opportunity to study three complete vertical sections through the distal facies of the TML through access to three drill cores. These cores, spaced 1500' (457m) apart and oriented oblique to inferred flow direction by 30°, are referred to here as cores A, B, and C, in a down-palaeoflow direction. Previous outcrop studies of the distal TML over the past century have concluded that the distal TML consists of a single flow. This is true of core B, which is dominated by a single 144' (44m) thick flow, underlain by a thin (∼5', 1.5m) flow with a vesiculated top, inferred to represent a toe of the thick flow, inasmuch as there is no baked zone or weathered contact between them. This contrasts sharply with core C, where the 50' (15.2m) thick TML consists of four flows 5-12' (1.6-3.6m) thick, each also defined by vesiculated tops, but differing in having weathered tops 1-2' (0.3-0.6m) thick, inferred to record an eruptive hiatus between each flow. The third flow in core C appears to be geochemically distinct from both overlying and underlying units, although all of the core samples are petrographically similar. The TML in cores C and B overlies coarse-grained andesitic volcaniclastic debris and fluvial deposits. By contrast, in core A, the TML overlies very fine-grained siltstones interpreted to record deposition in still water, probably a small lake produced by damming of the river by the thick flow in core B. The TML in core A is 20' (6m) thick, and is composed of eleven 1-3' (0.3-1.0m) thick couplets, each consisting of a clay-altered hyaloclastite breccia passing upwards into a relatively fresh, nonbrecciated, vesiculated top. We interpret these couplets to represent thin toes of a flow that generated steam explosions when they came into contact with a standing body of water. Palaeomagnetic remanence data (inclination only) on lava flows from the cores are consistent with the Classic Table Mountain direction and inconsistent with directional results from any other Stanislaus Group lava flows published to date. Thus, by palaeomagnetic correlation, the lavas studied here were emplaced between 10.36 ± 0.06 and 10.41 ± 0.08Ma. In addition, remanence results suggest that the three sampled flows from core C were erupted over a time period shorter than the secular variation rate (i.e. less than a few centuries) and the Knights Ferry portion of the TML was emplaced within several centuries of the average Classic TML age range spanning the Sierra Nevada. This indicates that the weathered flow tops at Knights Ferry formed very quickly.
AUTHOR KEYWORDS: Ancestral Cascades arc; high-K magmatism;  Sierra Nevada
DOCUMENT TYPE: Article
SOURCE: Scopus

Appelquist, K.a , Eliasson, T.b , Bergström, U.b , Rimša, A.c 
The Palaeoproterozoic Malmbäck Formation in S Sweden: Age, composition and tectonic setting
(2009) GFF, 131 (3), pp. 229-243. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70949096918&partnerID=40&md5=4744ff4735cd65dc65c8e89a8a251c1a
AFFILIATIONS: University of Gothenburg, Department of Earth Sciences, Box 460, Göteborg 405 30, Sweden; 
Geological Survey of Sweden, Guldhedsgatan 5A, Göteborg 413 20, Sweden; 
Geological Survey of Sweden, Box 670, Uppsala 751 28, Sweden
ABSTRACT: The Palaeoproterozoic Malmbäck Formation in southern Sweden comprises mafic to felsic volcanic rocks and syn-eruptive volcaniclastic and volcanogenic sedimentary deposits. Field observations indicate terrestrial to fluvial deposits - predominantly with massive to highly vesicular lavas, but also with ignimbrites, ashes, redeposited volcanic rocks and conglomerates. Three groups of volcanic rocks can be distinguished geochemically: (1) primitive basalts to basaltic andesites, (2) dacitesandesites and (3) rhyolites. The groups constitute a calc-alkaline to shoshonitic series. Large ion lithophile elements and light rare earth elements enrichment, combined with depletion in heavy rare earth elements and high field strength elements, particularly in Nb (and Ta), are characteristic of typical arc rocks. Discriminant diagrams suggest emplacement along a one-time active continental margin, which is now marked by the Transscandinavian Igneous Belt (TIB): an array of ~1.85-1.65 Ga granitic to gabbroic plutonic rocks and associated volcanic rocks more than 1000 km long. In the TIB, the Malmbäck Formation forms mega-xenoliths and other inclusions. U-Pb secondary ion mass spectrometry dating of zircon from a rhyolite of the Malmbäck Formation yielded a concordia age of 1796 ± 7 Ma, which is interpreted as the crystallisation age of the rhyolite and the age of deposition of the Malmbäck Formation, during a relatively early part of the formation period of the TIB. Altogether, the setting, composition and age of the Malmbäck Formation and the TIB confirm the existence of an Andean-type active continental margin in the present southern part of the TIB at c.1.8 Ga.
AUTHOR KEYWORDS: Active continental margin;  Dating;  Geochemistry;  Malmbäck Formation;  Palaeoproterozoic;  Sweden;  Transscandinavian Igneous Belt;  U-Pb;  Zircon
DOCUMENT TYPE: Article
SOURCE: Scopus

Praveen, M.N.a , Ghosh, B.b 
Submarine volcanic facies and its implication as possible tracker of sulphide mineralization - a study from Jilharidev area, betul belt, central India
(2009) Current Science, 97 (5), pp. 670-679. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-71849100514&partnerID=40&md5=6edb7d7ee042e9ad5e315f9b4b3edb77
AFFILIATIONS: Geological Survey of India, Southern Region, Kerala Unit, Thiruvananthapuram 695 014, India; 
Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India
ABSTRACT: Felsic volcaniclastic rock forms part of host rock sequences in many of the base metal prospects in the Betul belt. However, the volcanic facies, fragmentation processes and depositional environments in mineralized areas are poorly understood because of the effects of synvolcanic hydrothermal alteration and subsequent regional metamorphism. A section in the Kanhan river valley, which exposes volcanics with relatively well preserved primary textures was mapped in detail to understand the disposition of the felsic volcanics namely rhyolite and to identify the various volcanic facies present within them (viz. massive, flow-banded, autobreccia and hyaloclastite). Four different facies types were distinguished based on phenocryst type, size and abundance. Presence of hyaloclastite autoclastic rocks and pillow lava and absence of pyroclastic deposits suggest a deep, submarine, passive, effusive-type volcanic setting. Autobreccia and hyaloclastite in the felsic volcanic sequence of the present study area lying within Betul Belt has similarities with well-known volcanic-hosted massive sulphide (VHMS) bearing areas in other parts of the world. Proper identification of the volcanic facies within highly altered host rocks near the deposits can help in building up facies models that would establish the genetic relationship between sulphide mineralization and the host-rock facies which in turn will have important implications for base metal exploration in the area.
AUTHOR KEYWORDS: Autobreccia;  Base metal exploration;  Betul belt;  Hyaloclastite;  Massive rhyolite;  Submarine volcanic facies
DOCUMENT TYPE: Article
SOURCE: Scopus

Hagan, J.C.a , Busby, C.J.a , Putirka, K.b , Renne, P.R.c  d 
Cenozoic palaeocanyon evolution, Ancestral Cascades arc volcanism, and structure of the Hope Valley-Carson Pass region, Sierra Nevada, California
(2009) International Geology Review, 51 (9-11), pp. 777-823. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-76449088988&partnerID=40&md5=959fad46c2fb2bbc22b8c311528bd605
AFFILIATIONS: Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106, United States; 
Department of Earth and Environmental Sciences, California State University, Fresno, CA 93710, United States; 
Berkeley Geochronology Center, 2455 Ridge Rd, Berkeley, CA 94709, United States; 
Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, United States
ABSTRACT: We use new geologic mapping, geochronological, and geochemical data on Tertiary volcanic, volcaniclastic, and intrusive rocks to investigate the volcanic, stratigraphic, and structural evolution of the Carson Pass region south of Lake Tahoe in the central Sierra Nevada. Volcanic and volcaniclastic rocks were deposited in east-west-trending palaeocanyons carved into Mesozoic granitic and metamorphic basement rocks; sediments were transported westwards towards the present-day Central Valley of California. In the Carson Pass-Hope Valley area, two palaeotributaries are preserved in faulted terrane east of the present-day Sierran crest (Hope Valley area); these merge at the crest to form one large, &gt;7km wide palaeocanyon that is undisrupted by faults west of the crest (Carson Pass-Kirkwood area). This single, large palaeocanyon roughly coincides with the present-day Mokelumne River drainage. New40Ar 39Ar dates and stratigraphic data east of the crest, integrated with previously published data west of the crest, constrain the ages of strata and unconformities within the Hope Valley-Carson Pass-Kirkwood palaeocanyon system. We interpret three major erosional unconformities to record uplift events at ca. 23-16, 13.5-11, and 10-7Ma. In other parts of the central Sierra, these uplift events are inferred to correspond to range-front faulting events. We propose the term 'Hope Valley Graben' for the structural feature mapped immediately east of the Sierran crest at Carson Pass. It is a nearly symmetrical full graben that offsets volcanic rocks as young as 6Ma at least 400m (1300 ft) on each of its bounding faults - herein named the Red Lake Fault on the west and the Hope Valley Fault on the east. However, we infer that faulting began before eruption of the 6Ma volcanic rocks for three reasons: (1) the graben-localized emplacement of one of the largest volcanic centres in the Sierra, the 6.34 ± 0.14-6.18 ± 0.14Ma Markleeville Peak Center; (2) andesite lava flows erupted at 6.22 ± 0.14Ma from the Red Lake Fault, and abut it within the graben; and (3) brecciated granite along the Red Lake Fault is intruded by altered andesite, indicating that the fault started slipping before magmatism ceased. Our stratigraphic and geochronologic data do not permit an estimate of the amount of pre-6Ma displacement in the Hope Valley graben. The geometry of the palaeocanyon system indicates that a dextral component of slip demonstrated for transtensional faults in other parts of the region did not operate in the Hope Valley graben.
AUTHOR KEYWORDS: Ancestral Cascades arc;  Sierra Nevada;  Walker Lane Belt
DOCUMENT TYPE: Article
SOURCE: Scopus

Adams, T.L.
Deposition and taphonomy of the Hound Island Late Triassic vertebrate fauna: Fossil preservation within subaqueous gravity flows
(2009) Palaios, 24 (9), pp. 603-615. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-78649526464&partnerID=40&md5=6d68bbf8696e850d168beddd0865553c
AFFILIATIONS: Southern Methodist University, Roy M. Huffington Department of Earth Sciences, Dallas, TX 75275, United States
ABSTRACT: Late Triassic marine vertebrates occur in the Hound Island Volcanics exposed on the eastern shore of Hound Island, southeastern Alaska. This fossil assemblage derived from slope deposits within an intra-arc basin of a volcanic island arc complex. It is associated with the allochthonous Alexander Terrane prior to its northern translation from tropical latitudes to its current latitude. Fossils occur within a 13-m-thick succession of interbedded calcareous shale and volcaniclastic-rich bioclastic limestone. The limestone layers are skeletal (vertebrate and invertebrate) packstones to wackestones and are interpreted as episodic thin-bedded turbidite and debris flow deposits that resulted from redeposition of slope sediments. Forty-seven vertebrate fossils were collected that consist of complete and fragmented cranial and postcranial elements belonging to Eosauropterygia, Thalattosauria, and Ichthyosauria, including the genus Shonisaurus. Bones are frequently disassociated and show predepositional abrasion and breakage. Another less common taphonomic mode is observed, characterized by several large associated elements, representing a single individual, found parallel to bedding and draped by shale. Rare Osteichthyes and Chondrichthyes teeth are also present. Bivalve and conodont fossils indicate a middle Norian age for the assemblage. © 2009 SEPM (Society for Sedimentary Geology).
DOCUMENT TYPE: Article
SOURCE: Scopus

Lowey, G.W.a , Long, D.G.F.b , Fowler, M.G.c , Sweet, A.R.c , Orchard, M.J.d 
Petroleum source rock potential of Whitehorse trough: A frontier basin in south-central Yukon
(2009) Bulletin of Canadian Petroleum Geology, 57 (3), pp. 350-386. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954669358&partnerID=40&md5=cc1f12f484c1d219caf1aa5a88dd56a8
AFFILIATIONS: Yukon Geological Survey Energy, Mines and Resources Government of Yukon 2099, 2nd Avenue (K-10), Whitehorse, YK Y1A 1B5, Canada; 
Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada; 
Geological Survey of Canada (Calgary), 3303 -33rd Street NW, Calgary, AB T2L 2A7, Canada; 
Geological Survey of Canada (Vancouver), 625 Robson Street, Vancouver, BC V6B 5J3, Canada
ABSTRACT: Whitehorse trough is a frontier basin in south-central Yukon that is thought to contain gas and possibly oil. It consists of up to 7000 m of sedimentary and volcanic rocks referred to as the Lewes River Group (Triassic), Laberge Group (Jurassic), and Tantalus Formation (Jura-Cretaceous). The Lewes River Group is informally subdivided into the Povoas and Aksala formations, and the Laberge Group is informally subdivided into the Richthofen, Nordenskiold and Tanglefoot formations. To evaluate the petroleum source-rock potential of this basin, over 600 samples from the Aksala, Richthofen, Tanglefoot and Tantalus formations from throughout the trough have been analyzed by Rock-Eval programmed pyrolysis and combustion and by study of thermal alteration indicies (TAI) of palynomorphs, conodont alteration indicies (CAI), and vitrinite reflectance. The Povoas and Nordenskiold formations were not sampled because they consist of volcanic and volcaniclastic rocks, respectively, and have no source rock potential. The analyses indicate that the Aksala formation is a poor source rock that is postmature with no hydrocarbon potential. The Richthofen formation is a poor source rock that is postmature with minor gas potential. The Tanglefoot formation is a good source rock that is immature to early mature and gas-prone. The Tantalus Formation is also a good source rock that is immature to early mature and gas-prone. The Tanglefoot and Tantalus formations contain petroleum fluid inclusions that were probably generated from within these units. The inclusions reveal homogenization temperatures of mostly between 75-115°C and reveal several distinct, but minor pulses of liquid petroleum (mainly 19-21°API, 23°-35°API and 40-46° API). Potential petroleum (gas) generative intervals occur at surface and in the shallow subsurface in deltaic mudstones (Tanglefoot formation) and fluvial mudstones (Tantalus Formation). The lateral extent of these intervals is unknown due to poor outcrop exposure and limited shallow drilling. Both the Tanglefoot and Tantalus formations are interpreted as potential source rocks and possibly effective source rocks. The most prospective areas for petroleum exploration are Five Finger Rapids, Division Mountain and Tantalus Butte and in the northern portion of Whitehorse trough.
DOCUMENT TYPE: Article
SOURCE: Scopus

Marx, R.a , White, J.D.L.a , Manville, V.b 
Sedimentology and allostratigraphy of post-240 ka to pre-26.5 ka lacustrine terraces at intracaldera Lake Rotorua, Taupo Volcanic Zone, New Zealand
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-69249131276&partnerID=40&md5=510c4baf0824e4f735ab6bd98a49368c
AFFILIATIONS: Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand; 
Institute of Geological and Nuclear Sciences, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand
ABSTRACT: Lake Rotorua partially occupies a nearly circular 20 km diameter volcano-tectonic depression formed at c. 240 ka by eruption of the voluminous Mamaku Ignimbrite. Three distinct lacustrine littoral terraces, defined on the basis of contrasting geomorphology and field relations, and separated by tephrostratigraphically dateable unconformities and basin-floor disconformities, fringe much of the lake basin. They are here correlated with former high-stands of the lake which resulted from the blockage and re-establishment of a number of alternative outlets due to tectonic activity and volcanism at both the host and adjacent volcanic centres. The unconformities allow division of the deposits into three allostratigraphic units, each of which is then characterised by elevation and sediment provenance. The < 240 ka, post-Mamaku alloformation comprises the highest terrace (up to 415 mASL), and represents the high-stand of an intracaldera lake accumulated in the newly created basin after the eruption of the Mamaku Ignimbrite. Considerable uncertainty surrounds the initial direction of overflow from this level, but the lake may have drained southwards for a period through the Hemo Gorge, through the Ngakuru Graben/Kapenga Caldera area and into the Waikato River catchment. The second alloformation, consisting of volcaniclastic sediments forming shoreline and littoral terraces at c. 380 m elevation developed after the eruption of the 60 ka Rotoiti/Earthquake Flat pyroclastic flows from the neighbouring Okataina Volcanic Centre blocked northern and southern routes out of the lake basin. A northeasterly outlet subsequently became established at a lower level through tectonic subsidence of the Tikitere Graben, creating a drainage path into the Haroharo caldera from where it flowed into the Bay of Plenty via the Kawerau Canyon. The post-36 ka Hauparu alloformation forms the third shoreline terrace at elevations up to 349 mASL. It is the product of a temporary high-stand from blockage of the Tikitere Graben drainage path by pyroclastic debris from the voluminous 36 ka Hauparu eruption. Subsequently, episodic growth of the Haroharo resurgent dome complex between 25 and 9 ka in the adjacent Okataina Volcanic Centre forced Lake Rotorua to rise above its post-Hauparu lowstand level to an elevation where it could overtop a drainage divide on the northern rim of Lake Rotoiti and gain access to the catchment of the Kaituna River, hence establishing the current outlet channel. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Allostratigraphy;  Caldera lake;  Lacustrine deposits;  Volcaniclastic sediments;  Volcanogenic flood
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Turner, S.a , Handler, M.b , Bindeman, I.c , Suzuki, K.d 
New insights into the origin of O-Hf-Os isotope signatures in arc lavas from Tonga-Kermadec
(2009) Chemical Geology, 266 (3-4), pp. 196-202. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68749090769&partnerID=40&md5=1a3bfe31dd1884481e4cbc6d02261653
AFFILIATIONS: GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia; 
School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, New Zealand; 
Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403, United States; 
Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan
ABSTRACT: O, Hf and Os isotope data are presented for lavas from the highly depleted Tonga-Kermadec arc. O isotope values overlap with those of MORB limiting the amount of interaction with the arc crust. δ18O does not increase northwards as would be expected from the ~ 4 fold increase in subduction rate if slab-derived fluids had high 18O/16O ratios. Thus, the overall northward decrease in HFSE concentrations likely reflects depletion due to prior melt extraction, not increasing extents of melting. Hf isotopes are strongly negatively correlated with Be isotopes consistent with mixing of subducted pelagic sediment into the mantle wedge and do not require Hf to be fluid mobile. With the exception of a boninite from the north Tongan trench, the northern Tonga lavas do not overlap the Hf isotope composition of either the Samoan plume or the subducting Louisville volcaniclastic sediments. Thus, the Pb isotope signatures in these lavas must have been added by fluids and sediment melts derived from the Louisville volcaniclastics with minimal mobilisation of Hf. This suggests conservative behaviour for this element due to the formation of residual zircon during partial melting of the subducted sediments. 187Os/188Os ranges from 0.1275 to 0.4731 and the higher Os isotope ratios reflect the sensitivity of this system to even minor interaction with altered arc crust. Conversely, the lowest Os ratios are subchondritic and indicate that transfer of radiogenic Os from the slab is not all pervasive and provide an important constraint on the composition of the mantle wedge. Remarkably, the least radiogenic sample is a dacite demonstrating that evolved magmas can develop by fractionation from mantle-derived magmas with minimal interaction with the arc crust. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Island arc lavas;  O, Hf, Os isotopes;  Samoa;  Tonga-Kermadec
DOCUMENT TYPE: Article
SOURCE: Scopus

Rouchon, V.a , Orberger, B.a , Hofmann, A.b , Pinti, D.L.c 
Diagenetic Fe-carbonates in Paleoarchean felsic sedimentary rocks (Hooggenoeg Formation, Barberton greenstone belt, South Africa): Implications for CO2 sequestration and the chemical budget of seawater
(2009) Precambrian Research, 172 (3-4), pp. 255-278. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67650251223&partnerID=40&md5=64b6448641aea0e29bb102fc4902aca6
AFFILIATIONS: Université Paris Sud XI, Département des Sciences de la Terre, UMR-IDES CNRS UPS 8148, Bât. 504, 91405 Orsay Cedex, France; 
University of KwaZulu-Natal, School of Geological Sciences, Private Bag X 54001, Durban, 4000, South Africa; 
Département des Sciences de la Terre et de l'Atmosphère, GEOTOP, Université du Québec à Montréal, CP 8888, H3C 3P8 Montréal, Que., Canada
ABSTRACT: In order to evaluate the potential of felsic sediments as a CO2-sink in the Archean, we studied felsic volcaniclastic/epiclastic sedimentary rocks of the 3.45 Ga Hooggenoeg Formation, Barberton greenstone belt, which were affected by metasomatic processes during seafloor alteration and diagenesis. Water-rock interactions leading to K-, Si- and CO2-metasomatism were quantified. The precursor rock, a K-metasomatized dacite, was leached of Ca, Mg, Fe, Na, Sr, and Ba and enriched in K, Rb and Si prior to erosion and deposition. The formation of K-mica and quartz (and minor K-feldspar) in the dacites suggests low pH metasomatic conditions, likely produced by hydrothermally induced circulation of hot, acidic and reduced Archean seawater in equilibrium with a high PC O2 atmosphere. Erosion and transport of K-metasomatized dacitic detritus away from the felsic volcanic centers resulted in the deposition of conglomerate, sandstone and shale by mass flow processes. Early diagenetic silicification affected mainly the fine-grained sediments with higher silica sorption capacity, forming impermeable layers, while sand-rich sediments were partly silicified and remained permeable. Trapped fluids precipitated two generations of Fe-rich dolomites and finally calcite. Up to 30 vol.% of siliciclastic coarse-grained sediment was replaced by carbonates in a shallow-burial, high heat-flow diagenetic regime (depth: ∼750 m, temperature: 80-160 °C), and likely throughout deposition of overlying volcano-sedimentary units. The carbon isotopic composition of Fe-rich dolomites (δ13CPDB = +1.9 to +2.4‰) and the strong Fe-Ca-Mg leaching of the Paleoarchean volcanic formations support the influence of seawater-derived fluids throughout CO2-metasomatism. For each gram of eroded dacite, the overall chemical exchange involved by K-Si-CO2-metasomatism was characterized by a mass transfer of Fe (1.2 mmol/g), Na (2.1 mmol/g) and O2- (2.0 mmol/g) to seawater. In contrast, seawater was depleted in Si (10 mmol/g), Ca (0.51 mmol/g), Mg (0.43 mmol/g), K (1.5 mmol/g) and H (0.93 mmol/g) during incorporation of these elements in the volcanic and sedimentary rocks. The average CO2 uptake by the sedimentary rocks studied here is estimated to be 1.8 mmol/g, in the same order of magnitude as previous estimates for the Paleoarchean basaltic crust. Although mafic-ultramafic rocks are the most abundant rocks in Paleoarchean greenstones belts, and represent the most important atmospheric CO2-sink upon seafloor alteration in the Paleoarchean, coarse felsic sedimentary rocks provide a non-negligible contribution to the build-up of the continental CO2 reservoir. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Archean;  Atmospheric CO2;  CO2-sequestration;  Diagenesis;  Fe-rich dolomite;  Seawater evolution
DOCUMENT TYPE: Article
SOURCE: Scopus

Mollel, G.F.a , Swisher, C.C.a , McHenry, L.J.b , Feigenson, M.D.a , Carr, M.J.a 
Petrogenesis of basalt-trachyte lavas from Olmoti Crater, Tanzania
(2009) Journal of African Earth Sciences, 54 (5), pp. 127-143. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-77954953207&partnerID=40&md5=dcf8758e485dcb5a2e4f4acc6dc1cf8a
AFFILIATIONS: Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854, United States; 
Department of Geosciences, University of Wisconsin-Milwaukee, 3209 N. Maryland Ave, Milwaukee, WI 53211, United States
ABSTRACT: Olmoti Crater is part of the Plio-Pleistocene Ngorongoro Volcanic Highland (NVH) in northern Tanzania to the south of Gregory Rift. The Gregory Rift is part of the eastern branch of the East African Rift System (EARS) that stretches some 4000km from the Read Sea and Gulf of Aden in the north to the Zambezi River in Mozambique. Here, we (1) characterize the chemistry and mineral compositions of lavas from Olmoti Crater, (2) determine the age and duration of Olmoti volcanic activity through 40Ar/39Ar dating of Olmoti Crater wall lavas and (3) determine the genesis of Olmoti lavas and the relationship to other NVH and EARS volcanics and (4) their correlation with volcanics in the Olduvai and Laetoli stratigraphic sequences.Olmoti lavas collected from the lower part of the exposed crater wall section (OLS) range from basalt to trachyandesite whereas the upper part of the section (OUS) is trachytic. Petrography and major and trace element data reflect a very low degree partial melt origin for the Olmoti lavas, presumably of peridotite, followed by extensive fractionation. The 87Sr/86Sr data overlap whereas Nd and Pb isotope data are distinct between OLS and OUS samples. Interpretation of the isotope data suggests mixing of enriched mantle (EM I) with high-μ-like reservoirs, consistent with the model of Bell and Blenkinsop [Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic compositions of East African carbonatites: implications for mantle heterogeneity. Geology 5, 99-102] for East African carbonatite lavas. The isotope ratios are within the range of values defined by Oceanic Island Basalt (OIB) globally and moderate normalized Tb/Yb ratios (2.3-1.6) in these lavas suggest melting in the lithospheric mantle consistent with other studies in the region.40Ar/39Ar incremental-heating analyses of matrix and anorthoclase separates from Olmoti OLS and OUS lavas indicate that volcanic activity was short in duration, lasting ∼200kyr from 2.01±0.03Ma to 1.80±0.01Ma. The age of Olmoti activity overlaps with ages reported for Ngorongoro Caldera, implying contemporaneous activity of multiple NVH volcanic centers during part of the eruption interval.Olmoti is considered the source for the bulk of interbedded volcanics and volcaniclastic deposits that comprise much of the upper Bed I section of nearby Olduvai Gorge, and part of the Laetoli sequence, both known for their well preserved fossils and archaeological remains. Age and chemical data reported here are compatible with those derived from tephra and lava interbedded in Bed I at Olduvai Gorge and from the Olpiro Beds at Laetoli. © 2009 Elsevier Ltd.
AUTHOR KEYWORDS: 40Ar/39Ar;  Geochemistry;  Nd isotopes;  Pb isotopes;  Petrology;  Sr isotopes
DOCUMENT TYPE: Article
SOURCE: Scopus

Caroff, M., Vidal, M., Bénard, A., Darboux, J.-R.
A late-Ordovician phreatomagmatic complex in marine soft-substrate environment: The Crozon volcanic system, Armorican Massif (France)
(2009) Journal of Volcanology and Geothermal Research, 184 (3-4), pp. 351-366. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649487943&partnerID=40&md5=49f55a370138acf72619b6e453018ab6
AFFILIATIONS: Université Européenne de Bretagne, Université de Brest, CNRS IUEM, 6 avenue Victor Le Gorgeu, CS 93837, F-29238 Brest cedex 3, France
ABSTRACT: The mafic lavas and the diabases of Crozon (Armorican Massif, France), belong to an anorogenic Ordovician volcanic complex, emplaced on a rifted passive margin in North Gondwana. Magma passed through syn-volcanic soft sedimentary substrate, which is today mostly composed of alternating sandstones and mudstones, from Llanvirn to Ashgill in age. Field observations together with microscopic studies and geochemical analyses of magmatic rocks lead us to propose a model of volcano formation which combines hydromagmatic processes, peperitic intrusions, a shallow submarine tephra settling, eruption-fed turbidity currents, and a pillow lava effusion. The Crozon outcrops can be used to reconstruct a complete cross-section from the root of the volcanic complex to the lavas and breccias emplaced on the sea floor. The sites expose: (i) a hypabyssal breccia containing mud chunks and coarse-grained diabase clasts with amoeboidal fine-grained magmatic material; (ii) bulbous peperitic sills and pillow-like lobes bearing a great quantity of sediment-derived enclaves of fluidal morphology; (iii) volcaniclastic breccias containing near-spherical magmatic clasts that resulted from the complete fragmentation of sills in the ductile regime; (iv) a rhythmic peperitic breccia interpreted as the product of mingling between thin lava flows and soft calcareous sediment. The Crozon volcanic form, resulting from explosive interaction with subsurface/surface water, was probably a subaqueous collapsed tuff cone. This upper part of the system is synchronous with an Ashgill carbonate sedimentation, which overlies an Ordovician siliciclastic succession deposited in shelf environments. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Armorican Massif;  Ordovician;  peperite;  phreatomagmatism;  volcanic breccias
DOCUMENT TYPE: Article
SOURCE: Scopus

Parlak, O.a  b , Rizaoǧlu, T.c , Baǧci, U.d , Karaoǧlan, F.a , Höck, V.e 
Tectonic significance of the geochemistry and petrology of ophiolites in southeast Anatolia, Turkey
(2009) Tectonophysics, 473 (1-2), pp. 173-187. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649637846&partnerID=40&md5=f266fa43632a1cc2362ab2c730dd9728
AFFILIATIONS: Çukurova Üniversitesi, Jeoloji Muhendisligi Bolumü, 01330 Balcali, Adana, Turkey; 
Adiyaman Üniversitesi, Mesleki ve Teknik Eǧitim Fakültesi, 02040 Adiyaman, Turkey; 
Sütçü Imam Üniversitesi, Jeoloji Muhendisligi Bolumü, 46100 Kahramanmaraş, Turkey; 
Mersin Üniversitesi, Jeoloji Mühendisliǧi Bölümü, Çiftlikköy 33342, Mersin, Turkey; 
University of Salzburg, Department of Geology and Geography, A-5020 Salzburg, Austria
ABSTRACT: The southeast Anatolian ophiolites form discontinuous linear belts of oceanic fragments immediately north of the Bitlis-Zagros suture, which marks a continental collision zone between the Arabian platform to the south and the Taurides to the north. The Late Cretaceous ophiolites in the southeast Anatolia are represented by the Ki{dotless}zi{dotless}ldaǧ in the Hatay area, the Göksun and the Berit to the north of Kahramanmaraş, İspendere in the Malatya area and Kömürhan-Guleman in the Elazi{dotless}ǧ area. The Göksun, Berit, İspendere, Kömürhan and Guleman ophiolites were attached to the base of the Tauride platform (i.e. the Malatya-Keban) along its northern active margin and intruded by the I-type calc-alkaline granitoids of Late Cretaceous age. In contrast, the Ki{dotless}zi{dotless}ldaǧ (Hatay) ophiolite was thrust over the Arabian passive margin in the south. The cumulate rocks in the ophiolites are represented by dunite, wehrlite, lherzolite, olivine clinopyroxenite, olivine gabbronorite, olivine gabbro, gabbronorite and gabbro. Highly magnesian olivines (Fo88 to 74) and pyroxenes (Mg#95 to 60) as well as highly calcic plagioclases (An95 to 68) from the cumulate rocks differ from oceanic equivalents, which mainly formed from a MOR basaltic melt. The order of crystallization in mineral phases, whole rock and mineral chemistry data from the cumulates suggest that the primary magma is compositionaly similar to that observed in modern island arc tholeiitic sequences. The volcanic and subvolcanic rocks exhibit tholeiitic compositions. Chondrite normalized REE, N-MORB normalized multi-element patterns and tectonic discrimination diagrams suggest the existence of two main types of parental basic magmas in the crustal rocks of the SE Anatolian ophiolites. These are (i) IAT series that characterize the Ki{dotless}zi{dotless}ldaǧ, Göksun, İspendere, Kömürhan and Guleman ophiolites and (ii) Low-Ti boninitic series known only in the Ki{dotless}zi{dotless}ldaǧ ophiolite. The geochemistry of the crustal rocks suggests that they formed in a suprasubduction zone tectonic setting, including arc-forearc environments in the southern Neotethys. These well-preserved plutonic oceanic crustal remnants mainly exhibit an intact ophiolite pseudostratigraphy and are overlain by a volcanic-sedimentary unit made up of alternations of basic to acidic extrusive rocks, debris flows, volcaniclastic sandstones and pelagic limestones, interpreted as a tholeiitic ensimatic island arc assemblage built on the suprasubduction zone type crust. The metamorphism of some of the ophiolites (i.e. Berit) in the SE Anatolia might be related to later stages of intraoceanic subduction during the evolution of the southern Neotethys. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Anatolia;  Arc-forearc;  Ensimatic arc;  Southern Neotethys;  SSZ spreading
DOCUMENT TYPE: Article
SOURCE: Scopus

López-Gómez, J.a , Martín-Chivelet, J.a , Palma, R.M.b 
Architecture and development of the alluvial sediments of the Upper Jurassic Tordillo Formation in the Cañada Ancha Valley, northern Neuquén Basin, Argentina
(2009) Sedimentary Geology, 219 (1-4), pp. 180-195. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67651174278&partnerID=40&md5=dad1066f85a26773d1ca89d7677fcf52
AFFILIATIONS: Instituto de Geología Económica, Departamento de Estratigrafía (CSIC-UCM), Facultad de Geología, C/Antonio Nováis 2, 28040 Madrid, Spain; 
Departamento de Ciencias Exactas y Naturales, Universidad de Buenos Aires-CONICET, Pabellón II, 1428 Buenos Aires, Argentina
ABSTRACT: The Upper Jurassic Tordillo Formation at Cañada Ancha area, northern Neuquén Basin, Argentina, comprises a multi-stage suit of predominantly alluvial sediments that is heterolithic in nature. In that suit, several lithofacies, architectural elements, and bounding surfaces of different order have been identified and their lateral and vertical distribution characterized. This analysis allowed the differentiation of 3 main units (lower, middle and upper), 20 subunits (C-1 to C-20), and the characterization of their alluvial styles. The lower unit (which comprises subunits C-1 to C-4) is mainly formed by fine- to medium-grained sandstones, which become medium- to coarse-grained towards the top. These sandstones characterize settings ranging from floodplains with isolated, unconfined flows, to more complex, vertically stacked, multi-storey sheet sandstones of braided fluvial systems. The middle unit (C-5 to C-10) is dominated by pale brown-grey fine-to coarse-grained sands and medium size subangular to angular conglomerates, which reflect amalgamated complexes of sandstone sheets and downstream accretion macroforms. Remarkably, this alluvial sedimentation was episodically punctuated by volcaniclastic flows. The upper unit (C-11 to C-20) consists of finer sediments, mainly pink to white fine-to medium grained sandstones and red to green siltstones. Towards the top, bioturbation becomes important, and also the presence of volcanosedimentary flows is noticeable. Fluvial settings include braided sheet sandstones with waning flood deposits evolving to isolated high-sinuosity fluvial systems, with flash flood deposits. At the top of this unit, facies may suggest marine influence. Vertical changes in the fluvial style result from both climatic and tectonic controls. A semiarid to arid climate and the active tectonism linked to the eastward migration of the Andean volcanic arc determined major bounding surfaces, fluvial style evolution and the presence of the volcano-sedimentary deposits. Different stages of high and low subsidence rates has been deduced from the vertical stacking of sediments. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Alluvial architecture;  Argentina;  Back-arc basin;  Kimmeridgian;  Neuquén Basin;  Tordillo Formation
DOCUMENT TYPE: Article
SOURCE: Scopus

Paredes, J.M.a , Giacosa, R.E.a  b , Heredia, N.c 
Sedimentary evolution of Neogene continental deposits (Ñirihuau Formation) along the Ñirihuau River, North Patagonian Andes of Argentina
(2009) Journal of South American Earth Sciences, 28 (1), pp. 74-88. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649094149&partnerID=40&md5=4ae5960ca8dbad6e8ad10bc5767ce990
AFFILIATIONS: Departamento de Geología, Universidad Nacional de la Patagonia San Juan Bosco, Ruta Provincial No 1, Km. 4, Ciudad Universitaria, 9005 Comodoro Rivadavia, Chubut, Argentina; 
SEGEMAR, Delegacion Regional Comahue, CC 228 (8332), General Roca, Río Negro, Argentina; 
Instituto Geológico y Minero de España, Avda. Real, 1, Parque Cientifico de La Granja, E24006 Leon, Spain
ABSTRACT: The sedimentary evolution of the Ñirihuau Formation (late Oligocene-middle Miocene) was studied along the southern margin of the Ñirihuau River, in the North Patagonian Andes. The 1300-m-thick section includes 15 epiclastic and volcaniclastic lithofacies which are grouped into five lithofacies associations: deep lacustrine, shallow lacustrine, fluvial channels, subaerial floodplains and volcaniclastic flows (lahar). Syn-eruptive and inter-eruptive stages are recorded along the Ñirihuau River section. The former consist of highly aggradational packages several tens of meters thick of ash-fall beds and lahar deposits. During inter-eruptive periods sedimentation took place mostly in shallow and deep lacustrine environments, with four cycles of lake expansion and contraction, and a minor proportion of fluvial deposits. Sedimentary supply originated from the northeast and northwest in the lower part of the unit through low to moderate sinuosity fluvial systems, flowing into a lake with high-gradient margins, and forming Gilbert-type deltas. The younger sections were sourced from the northeast, east and southeast, indicating changes in the basin morphology. Basic and intermediate volcanic rocks similar to those of the Ventana Formation (Oligocene) are interstratified at the beginning of the sedimentation. The syn-orogenic nature of the Ñirihuau Formation is evidenced by the changes in the basin shape, but mainly by the differences in styles and intensities of deformation between the Ñirihuau River section and the overlying outcrops of La Buitrera Hill, both separated by a folded unconformity. © 2009 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Lacustrine and fluvial palaeoenvironments;  Miocene foreland basin;  Ñirihuau Formation;  North Patagonian Andes;  Patagonia
DOCUMENT TYPE: Article
SOURCE: Scopus

Mazumder, R.a , Arima, M.b 
Implication of mafic magmatism in an intracontinental rift setting: A case study from the paleoproterozoic dhanjori formation, singhbhum crustal province, India
(2009) Journal of Geology, 117 (4), pp. 455-466. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349117353&partnerID=40&md5=7e3ab11f0666221d78b69d693bad56fe
AFFILIATIONS: Geological Studies Unit and Fluvial Mechanics Laboratory, Indian Statistical Institute, 203, B.T. Road, Kolkata 700108, India; 
Graduate School of Environment and Information Sciences, Yokohama National University, 79-7, Tokiwadai, Hodogaya, Yokohama 240 8501, Japan
ABSTRACT: We present major, trace, rare earth element, and selected high-field-strength element ratios (Nb/Th, Zr/Nb, Nb/Y, and Zr/Y) of the Paleoproterozoic Dhanjori volcanic and volcaniclastic rocks of the Singhbhum crustal province, eastern India. The geochemical characteristics of the upper Dhanjori volcanic rocks indicate that these are basaltic komatiites. Our geochemical data, in combination with the sedimentological and stratigraphic characteristics of theinterbanded metasedimentary rocks clearly indicate an intracontinental rift setting for Dhanjori volcanism and sedimentation. © 2009 by The University of Chicago.
DOCUMENT TYPE: Article
SOURCE: Scopus

DeWolfe, Y.M.a  b , Gibson, H.L.a , Lafrance, B.a , Bailes, A.H.c  d 
Volcanic reconstruction of Paleoproterozoic arc volcanoes: The Hidden and Louis formations, Flin Flon, Manitoba, Canada
(2009) Canadian Journal of Earth Sciences, 46 (7), pp. 481-508. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349578939&partnerID=40&md5=306a77e256bb8658b0679706c4f4c855
AFFILIATIONS: Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, 933 Ramsey Lake Road, Sudbury, ON P3E 6C7, Canada; 
Department of Earth Sciences, Mount Royal College, 4825 Mount Royal Gate SW, Calgary, AB T3E 6K6, Canada; 
Manitoba Science, Technology, Energy and Mines, Manitoba Geological Survey, Suite 360 1395 Ellice Avenue, Winnipeg, MB R3G 3P2, Canada; 
Bailes Geoscience, 6 Park Grove Drive, Winnipeg, MB R2J 3l6, Canada
ABSTRACT: The hanging wall to the Flin Flon, Callinan, and Triple 7 volcanogenic massive sulphide deposits of the Flin Flon district is composed of the Hidden and Louis formations. The contact between these formations is marked by mafic tuff that represents a hiatus in effusive volcanism. The formations form a composite volcanic edifice that was erupted and grew within a large, volcanic-tectonic subsidence structure (hosting the deposits) that developed within a rifted-arc environment. The formations are evidence of resurgent effusive volcanism and subsidence following a hiatus in volcanism marked by ore formation since they consist of dominantly basaltic flows, sills, and volcaniclastic rocks with subordinate basaltic andesite and rhyodacitic flows and volcaniclastic rocks. The Hidden formation is interpreted to represent a small shield volcano and the Louis formation a separate shield volcano that developed on its flank. Both the Hidden and Louis volcanic edifices were constructed by continuous, low-volume eruptions of pillow lava. A gradual change from a dominantly extensional environment during the formation of the footwall Flin Flon formation to a progressively more dominant convergent environment during the emplacement of the hanging wall suggests that the Hidden and Louis formations are unlikely to host significant volcanogenic massive sulphide-type mineralization. However, synvolcanic structures in the formations define structural corridors that project downwards into the footwall where they encompass massive sulphide mineralization, indicating their control on ore formation, longevity,and reactivation as magma and fluid pathways during the growth of the Hidden and Louis volcanoes.
DOCUMENT TYPE: Article
SOURCE: Scopus

Romagnoli, C.a , Casalbore, D.a , Chiocci, F.L.b  c , Bosman, A.b  c 
Offshore evidence of large-scale lateral collapses on the eastern flank of Stromboli, Italy, due to structurally-controlled, bilateral flank instability
(2009) Marine Geology, 262 (1-4), pp. 1-13. Cited 7 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67349110399&partnerID=40&md5=68501f8fcf2f1bb309ebab01895df686
AFFILIATIONS: University of Bologna, Dip. Scienze della Terra e Geologico-Ambientali, P.zza di Porta S. Donato 1, 40126 Bologna, Italy; 
University of Roma La Sapienza, Dip. Scienze della Terra, P.le Aldo Moro 5, Roma, 00185, Italy; 
CNR, Istituto di Geologia Ambientale e Geoingegneria (IGAG), Area della Ricerca di Roma 1Via Salaria Km 29, 300 - C.P. 10 00016, Monterotondo Stazione, Roma 00100, Italy
ABSTRACT: New detailed swath bathymetry and long-range side scan sonar data on the submerged flanks of Stromboli, integrated with seismic data and seabed sampling, indicate that repeated lateral instability processes occurred on the eastern flank of the volcano, although no debris avalanche deposits were known before the high-resolution exploration of the seabed. This flank of the island is opposite to the northwestern side, more evidently affected by repeated flank collapses, and this setting is evidence for a structurally-controlled, bilateral flank instability of the volcanic edifice. Evidence of at least two large-scale lateral collapses is represented by a superficial hummocky megablock field, partially outcropping on the middle-lower eastern submerged slope, and by a chaotic unit (estimated volume is 1-2 km3) actually embedded within the volcaniclastic sequence at the foot of the submerged flank. A main submarine scar open towards the SE is carved in the upper slope on the eastern flank of the island, being partially filled with gravity flow deposits owing to the present-day depositional setting of the volcano's submerged flank. A morphological continuity can be envisaged between this submerged scar and an inferred subaerial one, likely encompassing the Rina Grande depression and several minor nested landslide scars recognized on the eastern Stromboli flank. A spatial and temporal reconstruction of possible events is proposed. The chaotic debris avalanche unit, buried within the volcaniclastic apron at the slope base and partially reworked in its distal part within the Stromboli Canyon floor, is thought to be the result of a lateral collapse event (called Paleostromboli Lateral Collapse, PLC, as it likely occurred in the earlier stages of the subaerial development of the island) affecting a wide sector of the eastern Stromboli flank. The megablock field might instead result from a more superficial debris avalanche deposit, partially eroded by gravity flows currently acting on the seabed. It is tentatively related to the recent subaerial scar morphologies affecting the Vancori units (and for this reason named Vancori Lateral Collapse, VLC). Displaced materials have lower volume and mobility than the PLC. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Aeolian Islands;  debris avalanche;  marine geophysical surveys;  submarine instability;  volcanic flank collapse
DOCUMENT TYPE: Article
SOURCE: Scopus

Owens, B.E., Wilson, S.E.
Geochemical constraints on the origin of chloritoid-bearing kyanite quartzite at Hagers Mountain, North Carolina
(2009) Southeastern Geology, 46 (3), pp. 135-153. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-69749084227&partnerID=40&md5=ba8dc6736f71688ad6f0ceb1a120048b
AFFILIATIONS: Department of Geology, College of William and Mary, Williamsburg, VA 23187, United States
ABSTRACT: A distinctive chloritoid-bearing kyanite quartzite occurs at Hagers Mountain, North Carolina, within the Hyco Formation of the Carolina terrane. Apart from the presence of chloritoid, rocks here are similar to occurrences in Virginia, including Willis Mountain (the site of the only active kyanite mine in the United States). Based on geochemical evidence, we interpret the rocks at Hagers Mountain to represent metamorphosed hydrothermally altered Si-rich volcaniclastic rocks. Extent of alteration increases from quartz-sericite schist → chloritoid-sericite quartzite → kyanite-chloritoid quartzite → kyanite quartzite. Kyanite quartzites (without chloritoid) represent the most intensely altered protoliths, an interpretation supported by unusual U-shaped rare earth element patterns (a feature shared with the Virginia occurrences). Evaluation of mass losses indicates slight (∼3%) to extensive (∼32%) leaching of various elements. Our interpretations of precursor mineralogy in order of increasing degree of alteration are: 1) quartz + sericite; 2) quartz + sericite + chlorite; 3) quartz + kaolinite + chlorite; and 4) quartz + kaolinite. Such mineral assemblages are typical of advanced argillic (high-sulfidation) alteration. Hagers Mountain rocks are similar to other examples of quartz-rich rocks that also contain chloritoid plus an aluminosilicate mineral. Such rocks are commonly associated either with volcanic hosted massive sulfide deposits or epithermal gold deposits, but have in common severe leaching of all mobile constituents in hot, acidic fluids prior to metamorphism.
DOCUMENT TYPE: Article
SOURCE: Scopus

Yagi, M.a , Ohguch, T.b , Akiba, F.c , Yoshida, T.d , Tiba, T.e 
The Fukuyama volcanic rocks: Submarine composite volcano in the Late Miocene to Early Pliocene Akita-Yamagata back-arc basin, northeast Honshu, Japan
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649099515&partnerID=40&md5=224ed6adde19933df788257e7312ae9b
AFFILIATIONS: Japan Petroleum Exploration Co., Ltd (JAPEX) Research Centre, 1-2-1 Hamada, Mihama-ku, Chiba 261-0025, Japan; 
Akita University, 1-1 Tegatagakuen-cho, Akita 010-8502, Japan; 
Diatom Mini-Lab Akiba Ltd., 632-12 Iwasawa, Hanno, 357-0023, Japan; 
Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan; 
The Kiseki Museum of World Stones, 3670 Yamamiya, Fujinomiya, Shizuoka 418-0111, Japan
ABSTRACT: The Fukuyama Volcanic Rocks are composed of pyroxene andesite (FKV-1), hornblende-pyroxene andesite (FKV-2), biotite-hornblende dacite (FKV-3) and volcaniclastic debris-flow deposits and/or turbidites. FKV-1, FKV-2 and FKV-3 are medium-K calc-alkaline rocks depleted in Nd, similar to other back-arc volcanic rocks of the northeast Japan arc and constitute a dome cluster at Fukuyama. Volcaniclastic beds surround the dome cluster and thin and fine upwards. The predominant clast type in the volcaniclastic beds changes upwards from pyroxene andesite, through hornblende-pyroxene andesite, to biotite-hornblende dacite, consistent with the stratigraphic relationships of FKV-1, FKV-2 and FKV-3 lavas. All the siltstones inter-bedded with the volcaniclastic beds and overlying the whole succession contain diatom fossils indicative of the lower part of the Thalassionema schraderi zone (7.8 Ma to 8.5 Ma), compatible with the isotopic ages of FKV-1, FKV-2 and FKV-3. The Fukuyama volcano has a total eruption volume of 60-100 km3, with a lifetime of the order of 105 years, as typically observed for volcanoes in the present back-arc region of northeast Honshu. FKV-1 erupted in deep water and partly disintegrated into hyaloclastite breccias due to direct contact with water. FKV-2 lava repeatedly effused over the FKV-1 lava and produced a volcanic apron of breccias that eventually grew above wave base and was eroded by wave action. The magma of FKV-3 was probably hydrous as it contains biotite and hornblende. The FKV-3 magma could have explosively erupted from a shallow-water dome or vent emergent above the wave base, followed by growth of a degassing lava dome. Repose between eruptions allowed accumulation of silt, and after the Fukuyama eruptions ceased silt entirely mantled the volcano. A small magma supply rate perhaps allowed a relatively long period of quiescence between eruptions of FKV-1, FKV-2 and FKV-3 magmas, resulting in abrasion and reworking of volcanic fragments and accumulation of non-volcanic sediments that constitute part of the volcaniclastic apron. Oil generated in the contemporaneous or underlying sediments, migrated to the upper levels of the volcaniclastic apron and accumulated there under the thick cover of fine-grained sediments that mantle the volcano. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Debris-flow deposit;  Japan;  Neogene diatom;  Northeast Honshu;  Post-rift volcanism;  Radiometric age;  Submarine volcanism;  Turbidite;  Volcanic reservoir
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Kataoka, K.S.a  b , Manville, V.b , Nakajo, T.c , Urabe, A.a 
Impacts of explosive volcanism on distal alluvial sedimentation: Examples from the Pliocene-Holocene volcaniclastic successions of Japan
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67249150700&partnerID=40&md5=02e7b982d078a847eb2758328d9f1dc6
AFFILIATIONS: Research Center for Natural Hazards and Disaster Recovery, Niigata University, Ikarashi 2-cho 8050, Nishi-ku, Niigata 950-2181, Japan; 
GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; 
Osaka Museum of Natural History, Nagai Park 1-23, Higashisumiyoshi-ku, Osaka 546-0034, Japan
ABSTRACT: Volcanic activities can create cataclysmic hazards to surrounding environments and human life not only during the eruption but also by hydrologic remobilisation (lahar) processes after the cessation of eruptive activity. Although there are many studies dealing with the assessment and mitigation of volcanic hazards, these are mostly concentrated on primary eruptive processes in areas proximal to active volcanoes. However, the influence of volcaniclastic resedimentation may surpass the impacts of primary eruptive activity in terms of both extent and persistence, and can ultimately result in severe hazards in downstream areas. Examination of the volcaniclastic successions of non-marine Pliocene-Holocene sedimentary basins in Japan has revealed hydrological volcaniclastic sedimentation in fluvial and lacustrine environments hundreds of kilometres from the inferred source volcano. Impacts on these distal and often spatially separated basins included drastic changes in depositional systems caused by sudden massive influxes of remobilised pyroclastic material. Typical volcaniclastic beds comprise centimetre- to decimetre-thick primary pyroclastic fall deposits overlain by metre- to 10s of metres-thick resedimented volcaniclastic deposits, intercalated in sedimentary successions of non-volcanic provenance. The relatively low component of primary pyroclastic fall deposits in the volcaniclastic beds suggests that: 1) potential volcanic hazards would be underestimated on the basis of primary pyroclastic fall events alone; and 2) the majority of resedimented material was likely derived from erosion of non-welded pyroclastic flow deposits in catchment areas rather than remobilisation of local fallout deposits from surrounding hillslopes. The nature, distribution and sequence of facies developed by distal volcaniclastic sediments reflect the influence of: 1) proximity to ignimbrite, but not directly with the distance to the eruptive centre; 2) ignimbrite nature (non-welded or welded) and volume; 3) temporal changes in sediment flux from the source area; 4) the physiography and drainage patterns of the source area and the receiving basin, and any intervening areas; and 5) the formation of ephemeral dam-lakes and intra-caldera lakes whose potential catastrophic failure can impact distal areas. Models of the styles and timing of distal volcaniclastic resedimentation are thus more complicated than those developed for proximal settings of stratovolcanoes and their volcaniclastic aprons and hence present different challenges for hazard assessment and mitigation. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Alluvial;  Explosive eruption;  Fluvial;  Lacustrine;  Lahar;  Volcaniclastic
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Yamamoto, T.
Sedimentary processes caused by felsic caldera-forming volcanism in the Late Miocene to Early Pliocene intra-arc Aizu basin, NE Japan arc
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67149133308&partnerID=40&md5=c9eb3360ebbc949f3f40b24460f0c347
AFFILIATIONS: Geological Survey of Japan, AIST, Tsukuba 305-8567, Japan
ABSTRACT: Six large Late Miocene to Quaternary calderas, > 10 km in diameter, cluster together with several medium to small calderas and stratovolcanoes in a 60 × 30 km area of the Aizu volcanic field, southern NE Japan arc. These caldera volcanoes were built on a WNW-ESE trending highland coincident with a local uplifted swell since Late Miocene. The flare-up of felsic volcanism occurred synchronously along the NE Japan arc. Pyroclastic flow sheets from the calderas spread over the surrounding intra-arc basins and are interstratified with various sediments. Geochronological data indicates that the large-caldera eruptions have occurred six times since 8 Ma, at intervals of 1 to 2 million years. Late Miocene to Early Pliocene extra-caldera successions in the basin consist of nine sedimentary facies associations: (1) primary pyroclastics, (2) lahars, (3) gravelly fluvial channels, (4) sandy fluvial channels, (5) floodplains, (6) tidal flats, (7) delta fronts, (8) pro-delta slopes, and (9) pro-delta turbidites. The distribution of facies associations show westward prograding of volcaniclastic aprons, made up of braid delta, braidplain, pyroclastic flow sheet, and incised braided river deposits. The extra-caldera successions record: 1) an increase in felsic volcanism with an associated high rate of volcaniclastic sediment supply at about 10 Ma, prior to catastrophic caldera-forming eruptions; and 2) progradation of volcaniclastic aprons toward the back-arc side in response to the succeeding caldera-forming eruptions and sea-level changes, until about 3 Ma. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Aizu;  Caldera;  Lahar;  NE Japan arc;  Pyroclastic flow;  Volcaniclastic apron
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Zernack, A.V., Procter, J.N., Cronin, S.J.
Sedimentary signatures of cyclic growth and destruction of stratovolcanoes: A case study from Mt. Taranaki, New Zealand
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67149130179&partnerID=40&md5=7659ab1c7da8f7dae1a9f7e2ac2e4872
AFFILIATIONS: Volcanic Risk Solutions, Institute of Natural Resources, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand
ABSTRACT: The long-term behaviour of andesite stratovolcanoes is characterised by a repetition of edifice growth phases followed by collapse. This cyclic pattern represents a natural frequency at varying timescales in the growth dynamics of stratovolcanoes worldwide. Around the > 130 ka Mt. Taranaki (Egmont volcano), New Zealand, coastal-cliff successions at 20-40 km distance comprise repeating packages of lithologically and sedimentologically distinctive mass-flow deposits. Varying depositional mechanisms and source properties of these units record growth and collapse cycles of the central edifice. These are used to construct a model for cyclic volcaniclastic sedimentation in the surrounds of stratovolcanoes. During edifice-construction phases, thick packages of tabular, predominantly monolithologic, hyperconcentrated-flow and debris-flow deposits accumulate with intercalated tephra beds. The mass-flow units commonly contain large proportions of fresh pumice or juvenile-lithic andesite. Intervals of quiescence separating eruptive periods are characterised by landscape re-adjustment, accompanied by deposition of fluvial and aeolian sediments, along with steady accretion of medial ash. In contrast, brief episodes of destruction are marked by wide-spread, distinctively clay-rich, polylithologic debris-avalanche deposits and related marginal debris flow units. The growth stages can be terminated by an eruption-triggered sector collapse, or by external forces once the edifice exceeds a critical stable height or profile (dependent on eruptive style and local geo-tectonic conditions). Once the edifice becomes metastable, regional tectonic earthquakes or shallow-level intrusion events are likely triggers for collapse. Although the resulting debris avalanches represent the greatest individual hazard from such andesite stratovolcanoes, their frequency is relatively low compared with other types of mass-flows generated during edifice-growth phases. Accurate forecasts of future hazard from mass-flow events are therefore dependent on recognition of both the frequency of a stratovolcano's growth cycle and its current position in that cycle. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Debris avalanche;  Debris flow;  Hyperconcentrated flow;  Lahar;  Mt. Taranaki/Egmont;  Volcaniclastic
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Manville, V.a , Németh, K.b , Kano, K.c 
Source to sink: A review of three decades of progress in the understanding of volcaniclastic processes, deposits, and hazards
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-66749101437&partnerID=40&md5=ad8f0c398a9fd29437fd9106c26aac39
AFFILIATIONS: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; 
Institute of Natural Resources, Massey University, PB 11-222, Palmerston North, New Zealand; 
Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1 Higashi 1-chome, Tsukuba, Ibaraki 305-8567, Japan
ABSTRACT: Volcaniclastic sediments, broadly defined as clastic deposits derived from the transport, deposition and/or redeposition of the products of volcanic activity, have long been a Cinderella of the geosciences. This status is a function of the inherent complexity of the fragmentation, transport and depositional processes that operate in volcanically-impacted environments and the comparatively recent development of the discipline as a specialist area. Volcaniclastic studies are truly interdisciplinary, drawing on many elements of physical volcanology, fluid dynamics, classical clastic sedimentology, hydrology and geomorphology. In the past 30 years volcaniclastic studies have blossomed, partly in response to a number of catastrophic and high-profile volcanic eruptions, including Mount St. Helens in 1981, Nevado del Ruiz in 1985 and Pinatubo in 1991, and partly due to integration with the maturing science of fluid dynamics and an increased understanding of the behaviour of particulate dispersions and two-phase granular flows. These historical events have demonstrated that the sedimentary repercussions of volcanic eruptions can have more severe, far-reaching, and prolonged impacts than the initial volcanism. In parallel, studies of well-preserved examples from the geological record have extended our understanding of landscape and environmental responses to styles and scales of volcanism that have not been recorded historically, such as the impacts of caldera-forming eruptions from silicic calderas. As a consequence, studies have expanded beyond classical stratigraphic and sedimentological studies of ancient successions in a variety of plate tectonic settings to a more dynamic focus on process. Ultimately, volcaniclastic successions are the product of the interplay between the volcano, in terms of the style, magnitude and explosivity of the eruption, and the environment, as expressed by physiography, hydrology, energy, and accommodation space. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Explosive volcanism;  Natural hazards;  Sedimentology;  Stratigraphy;  Volcaniclastic sedimentation
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Németh, K.a , Cronin, S.J.a , Stewart, R.B.a , Charley, D.a  b 
Intra- and extra-caldera volcaniclastic facies and geomorphic characteristics of a frequently active mafic island-arc volcano, Ambrym Island, Vanuatu
(2009) Sedimentary Geology, 218 (1-4), pp. 174-188. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67349260819&partnerID=40&md5=e56ffdb9430a7cf959040cd3a610adcf
AFFILIATIONS: Institute of Natural Resources, Volcanic Risk Solutions, Massey University, Private Bag 11 222, Palmerston North, New Zealand; 
Department of Geology, Mines and Water Resources, Port Vila, Vanuatu
ABSTRACT: Ambrym is one of the most voluminous active volcanoes in the Melanesian arc. It consists of a 35 by 50 km island elongated east-west, parallel with an active fissure zone. The central part of Ambrym, about 800 m above sea level, contains a 12 kilometre-wide caldera, with two active intra-caldera cone-complexes, Marum and Benbow. These frequently erupting complexes provide large volumes of tephra (lapilli and ash) to fill the surrounding caldera and create an exceptionally large devegetated plateau "ash plain", as well as sediment-choked fluvial systems leading outward from the summit caldera. Deposits from fall, subordinate base surge and small-volume pyroclastic (scoria) flows dominate the volcaniclastic sequences in near vent regions. Frequent and high-intensity rainfall results in rapid erosion of freshly deposited tephra, forming small-scale debris flow- and modified grain flow-dominated deposits. Box-shaped channel systems are initially deep and narrow on the upper flanks of the composite cones and are filled bank-to-bank with lapilli-dominated debris flow deposits. These units spill out into larger channel systems forming debris aprons of thousands of overlapping and anastomosing long, narrow lobes of poorly sorted lapilli-dominated deposits. These deposits are typically remobilised by hyperconcentrated flows, debris-rich stream flows and rare debris flows that pass down increasingly shallower and broader box-shaped valleys. Lenses and lags of fines and primary fall deposits occur interbedded between the dominantly tabular hyperconcentrated flow deposits of these reaches. Aeolian sedimentation forms elongated sand dunes flanking the western rim of the ash-plain. Outside the caldera, initially steep-sided immature box-canyons are formed again, conveying dominantly hyperconcentrated flow deposits. These gradually pass into broad channels on lesser gradients in coastal areas and terminate at the coast in the form of prograding fans of ash-dominated deposits. The extra-caldera deposits are typically better sorted and contain other bedding features characteristic of more dilute fluvial flows and transitional hyperconcentrated flows. These outer flank volcaniclastics fill valleys to modify restricted portions of the dominantly constructional landscape (lava flows, and satellite cones) of Ambrym. Apparent maturity of the volcanic system has resulted in the subsidence of the present summit caldera at a similar rate to its infill by volcaniclastic deposits. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Ambrym;  Caldera;  Grain flow;  Hyperconcentrated flow;  Tephra;  Vanuatu;  Volcanic sedimentology
DOCUMENT TYPE: Article
SOURCE: Scopus

Bedatou, E.a , Melchor, R.N.a , Genise, J.F.b 
Complex palaeosol ichnofabrics from Late Jurassic-Early Cretaceous volcaniclastic successions of Central Patagonia, Argentina
(2009) Sedimentary Geology, 218 (1-4), pp. 74-102. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67349220153&partnerID=40&md5=b7ceecf3234cc4c77637478062596fd3
AFFILIATIONS: CONICET, Universidad Nacional de La Pampa, Av. Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina; 
CONICET, Museo Paleontológico Egidio Feruglio, Av. Fontana 140, 9100 Trelew, Chubut, Argentina
ABSTRACT: Late Jurassic-Early Cretaceous volcaniclastic continental deposits from central Patagonia, Argentina were analyzed for an integral characterization of palaeosol ichnofabrics. These units contain complex continental ichnofabrics that were also recorded in other late Jurassic-late Miocene extended volcaniclastic successions from Patagonia. According to a recently proposed method, ichnofabric, pedofabric and original bedding of selected intervals were measured separately in order to determinate the degree in which the deposits are affected by soil features besides the ichnofabrics. Four recurrent ichnofabrics were recognized in studied palaeosols: the Loloichnus, large Taenidium-Beaconites, diffuse boxwork, and Dagnichnus ichnofabrics. The Loloichnus ichnofabric is characterized by sub-vertical Loloichnus baqueroensis and subordinate, similarly arrenged large Taenidium barretti and Beaconites coronus. L. baqueroensis is a crayfish dwelling structure while large T. barretti and B. coronus are assigned to locomotion of the same organisms. Root traces are additional components of this ichnofabric. The large Taenidium-Beaconites ichnofabric is formed by large, irregular and curved T. barretti and B. coronus and by L. baqueroensis in low proportion. This ichnofabric is also assigned to crayfish activity. The diffuse boxwork ichnofabric is characterized by a pervasive and intricate three-dimensional boxwork of burrows; occasionally joined to subspherical chambers (possible Castrichnus). The diffuse boxwork is interpreted as an earthworm burrow system and the associated chambers are probably for aestivation. Rare and scattered discrete trace fossils in this ichnofabric include L. baqueroensis, T. barretti and B. coronus. The Dagnichnus ichnofabric is formed by Dagnichnus titoi, root traces and, subordinately, Loloichnus baqueroensis, Cellicalichnus meniscatus and tangled groups of meniscate burrows. D. titoi and C. meniscatus has been interpreted as crayfish breeding structures and the tangled groups of meniscate burrows are probably related to juvenile crayfish activity. The studied ichnofabrics were formed in weakly to moderately developed palaeosols in lowland areas with frequent reworking of pyroclastic material by unconfined flows. The recognized ichnofabrics show that in Patagonia, for the Late Jurassic-Early Cretaceous times, crayfishes and earthworms were the dominant soil organisms and, along with plants, rapidly colonized deposits exposed subaerially. After sediment deposition and with high soil moisture content or high water table crayfishes probably crawled in moist sediments forming the large Taenidium-Beaconites ichnofabric. With a better drained soil profile or lower water tables, the Loloichnus ichnofabric, representing the dwelling structures of adult crayfishes, overprinted the previous ichnofabric. The diffuse boxwork ichnofabric, usually located in the uppermost portion of palaeosols, correspond to extensive fossil earthworm burrow systems. The Dagnichnus ichnofabric occurs in very weakly developed palaeosols and probably reflects the optimal palaeoenvironmental conditions for breeding crayfish. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Ichnofabrics;  Mesozoic;  Palaeosols;  Patagonia;  Trace fossils
DOCUMENT TYPE: Article
SOURCE: Scopus

Manville, V.a , Segschneider, B.b , Newton, E.b , White, J.D.L.b , Houghton, B.F.c , Wilson, C.J.N.d 
Environmental impact of the 1.8 ka Taupo eruption, New Zealand: Landscape responses to a large-scale explosive rhyolite eruption
(2009) Sedimentary Geology, 218 (1-4), pp. 155-173. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67349174232&partnerID=40&md5=879382835023c4cabf731cbbc1731d4b
AFFILIATIONS: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; 
Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand; 
Department of Geology and Geophysics, SOEST, University of Hawaii at Manoa, Honolulu, HI 96822, United States; 
Geology-SGGES, University of Auckland, Private Bag 92019, Auckland, New Zealand
ABSTRACT: Large-scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material. The post-eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology, exemplified here by the 1.8 ka Taupo eruption in the central North Island of New Zealand. This eruption generated voluminous fall deposits, then climaxed with emplacement of a c. 30 km3 non-welded ignimbrite over a near-circular area of c. 20 000 km2. Approximately 90% of the area, but &lt; 50% of the ignimbrite volume, is represented by a landscape-mantling unit that covered the pre-eruption topography to a depth varying from c. 10 m in proximal areas to less than 15-30 cm distally. The remainder of the ignimbrite deposit is represented by landscape-modifying material that ponded in valley bottoms and depressions to thicknesses of up to 70 m, with no systematic variation in thickness with distance from source. The headwaters of many of the North Island's largest rivers were impacted by both the primary pyroclastic fall and flow material. Large-scale post-eruption remobilisation of this material, coupled with the re-establishment of fluvial systems, occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub-environments. Following an initial period dominated by mass flows, re-establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits, a process often associated with the break-out of temporary lakes. Aggradational streams developed in these channels rapidly evolved from shallow, ephemeral, sediment-laden outbursts associated with flash flood events to deeper, permanent braided rivers, before declining sediment yields led to retrenchment of single thread rivers and a return to pre-eruption gradients and bedloads years to decades later. Typically the modern profile of many streams and rivers follow closely their pre-eruption profiles, and incision and erosion is overwhelmingly confined to the deposits of the eruption itself. Although the general remobilisation pattern is similar for all impacted river systems, detailed studies of the Waikato, Rangitaiki, Mohaka, Ngaruroro and Whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment. These reflect differences in catchment physiography and hydrology, and the volume and type of pyroclastic material deposited in each. Ultimately, the landscape response reflects the relative spatial distributions of, and the volumetric ratios between, the volumes of pyroclastic debris, water, and accommodation space in the basin (cf. Kataoka and Manville, this volume). © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Fluvial sedimentology;  Lahar;  Pumice;  Taupo ignimbrite;  Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Kolb, J.a  b  c , Hagemann, S.b 
Structural control of low-sulfidation epithermal gold mineralization in the Rosario-Bunawan district, East Mindanao Ridge, Philippines
(2009) Mineralium Deposita, 44 (7), pp. 795-815. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349994303&partnerID=40&md5=71d9faba36fab8300054b21b6f103b89
AFFILIATIONS: Department of Economic Geology, Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen, Denmark; 
Centre for Exploration Targeting (CET), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia; 
Institute for Mineralogy and Economic Geology, RWTH Aachen University, Wüllnerstr. 2, 52056 Aachen, Germany
ABSTRACT: The Rosario-Bunawan district is situated about 200 km north of Davao City, the capital of the Mindanao Island, Southern Philippines. Gold is produced from the Co-O mine, containing about 2,034,000 t of ore at 10.9 g/t Au, and in numerous small-scale operations by local miners. Epithermal gold mineralization in the Rosario-Bunawan district and the Co-O mine is confined to narrow (0.2-4 m) low-sulfidation quartz-chalcedony-calcite veins in volcanic and volcaniclastic wall rocks. Three major vein orientations are distinguished: (1) the NNW-SSE-trending set with a sinistral strike-slip sense of deformation (Philippine Fault trend); (2) the ENE-WSW-trending dextral strike-slip set (Palawan trend) and associated veins in the Riedel geometry; and (3) the WNW-ESE-trending conjugate set (Co-O trend). Three structural stages are defined: (1) extensional shear or shear veins formed in the Co-O, the Philippine Fault, and Palawan trends during regional NW-SE compression and near vertical vein opening (D1); (2) reactivation of veins in the Philippine Fault, veins associated with the Palawan, and, to a lesser extent, the Co-O trends during E-W compression and near horizontal N-S-oriented vein opening (D2). New D2 extensional shear or shear veins formed in the Philippine Fault, and structures associated with the Palawan and associated Riedel trends; (3) the D3-stage block faulting subsequently displaced all of the auriferous veins. The auriferous Rosario-Bunawan district is situated between two splays of the Philippine Fault, which acted as a lateral ramp system during the oblique convergence of the Philippine Sea plate and the Eurasian plate. The oblique convergence resulted in a change from a compressional (D1) to a transpressional (D2) regime, which was a prerequisite for the two-stage vein opening and hydrothermal mineralization, leading to an economic gold enrichment. D1 compressional tectonics may have caused an elevated geothermal gradient in shallow crustal levels, forming the heat source for the fluid plumbing system, which is at variance to typical epithermal deposits formed in extensional zones. D2 thrusting of a limestone nappe together with syn-tectonic diorite intrusions may have further increased the geothermal gradient, maintaining the fluid plumbing system. The limestone nappe may, at the same time, have represented an aquitard forcing the hydrothermal fluids into the volcanic and volcaniclastic wall rocks, which is regarded as critical for the two-stage gold mineralization in the Rosario-Bunawan district. © Springer-Verlag 2009.
AUTHOR KEYWORDS: Epithermal gold veins;  Low-sulfidation gold;  Mindanao;  Philippines;  Rosario-Bunawan
DOCUMENT TYPE: Article
SOURCE: Scopus

Nemeth, K.a , Manville, V.b , Kano, K.c 
Source to sink - Volcaniclastic sedimentation in and around the Pacific
Sedimentary Geology, . Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-66149094320&partnerID=40&md5=8d8798a2678a3b283da106026333b7cc
AFFILIATIONS: Volcanic Risk Solutions, Massey University, PO Box 11 222, Palmerston North, New Zealand; 
GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; 
Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology Tsukuba Central 7 1-1 Higashi 1-chome, Tsukuba, Ibaraki 305-8567, Japan
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Umazano, A.M.a , Bellosi, E.S.b , Visconti, G.c , Jalfin, G.A.d , Melchor, R.N.a 
Sedimentary record of a Late Cretaceous volcanic arc in central Patagonia: petrography, geochemistry and provenance of fluvial volcaniclastic deposits of the Bajo Barreal Formation, San Jorge Basin, Argentina
(2009) Cretaceous Research, 30 (3), pp. 749-766. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-64549119065&partnerID=40&md5=dc7f3770b34b1957bde8b484848e44a8
AFFILIATIONS: Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa., Av. Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina; 
Consejo Nacional de Investigaciones Científicas y Técnicas, Museo Argentino de Ciencias Naturales., Av. Ángel Gallardo 470, 1405 Buenos Aires, Argentina; 
Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa., Av. Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina; 
IPM, Schlumberger, Schlumberger House, Buckingham Gate, Gatwick Airport, RH6 0NZ, United Kingdom
ABSTRACT: The Upper Cretaceous Bajo Barreal Formation (San Jorge Basin, Argentina) is a fluvial succession mostly composed of channel sandstones interbedded with thicker floodplain deposits dominated by tuffaceous strata. The goal of this contribution is to infer the provenance of the unit through combined petrographical and geochemical data of channel sandstones, primary tuffs and tuffo-psammites (reworked, no-mixed tuffs). Channel sandstones are dominantly litharenites and feldspathic litharenites with abundant participation of volcanic lithic fragments with different textures (porphyritic, eutaxitic, felsitic, pilotaxitic, trachytic and vitric-vitrophyric), pumice and plagioclase. K-feldspar, quartz and sedimentary rock fragments are scarce. QFLu diagram and several provenance indicators including dominance and textural types of rock fragments, K-feldspar/plagioclase ratio and inclusion-free quartz grains indicate a provenance from felsic to intermediate, pyroclastic-rich, arc-related volcanic rocks. This interpretation agrees with the values of various elemental ratios of trace elements such as La/Sc, Th/Sc, Cr/Th, Eu/Eu* and (La/Lu)N and discriminant functions based on major elements. Pyroclastic floodplain strata are commonly pumice-rich, occasionally glass shard-rich, vitric tuffs suggesting an origin from plinian-like eruptions. Subordinate components include volcanic lithic fragments, quartz, orthoclase and plagioclase. Zr/Ti versus Nb/Y and SiO2 versus K2O diagrams, as well as a multi-element diagram of selected trace elements shows that the pyroclastic rocks were originated from medium-K content, intermediate, arc related magmatic source. Considering the palaeoflow direction towards the east and south-east and presence of subduction processes along the western margin of Patagonia during the Late Cretaceous, it is interpreted that Bajo Barreal Formation constitutes the sedimentary record (distal facies of volcano-flanking fan or apron) of this coeval volcanic arc. Channel sandstones probably were mostly derived from the Divisadero Formation volcanic rocks because of similar petrographical features and REE pattern. In contrast, pyroclastic tuffaceous floodplain deposits would be derived from vents located over the actual outcrops of the Patagonian Batholith. © 2009 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Geochemistry;  Late Cretaceous;  Patagonia;  Petrography;  Provenance
DOCUMENT TYPE: Article
SOURCE: Scopus

Zoheir, B.a , Akawy, A.b 
Epigenetic BIF-hosted gold lodes at the Abu Marawat area, Eastern Desert, Egypt: Integrated mineralogical, structural control and fluid inclusion studies
(2009) Transactions of the Institutions of Mining and Metallurgy, Section B: Applied Earth Science, 118 (2), pp. 59-76. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350219102&partnerID=40&md5=64afa26d78839b80d8de7c6efbaec5a9
AFFILIATIONS: Department of Geology, Faculty of Science, Benha University, Benha 13518, Egypt; 
Department of Geology, Faculty of Science, South Valley University, Qena 81528, Egypt
ABSTRACT: Numerous massive and sheared, milky quartz veins cut a sequence of Neoproterozoic island arc metavolcanic/volcaniclastic rocks and related banded iron formation (BIF) at the Abu Marawat area, central Eastern Desert of Egypt. Sulphide-bearing quartz veins and related hydrothermal breccia masses display a range of textures including sheared, boudinaged and recrystallised quartz, quartz with open space filling and microbreccia, implying a complex history of crack-seal processes characterising the relationship between mineral deposition and a major N-S-trending shear zone, during a late brittle-ductile deformation event that affected the area at ∼550 Ma. Gold-base metal mineralisation is associated with brecciation and fracturing of the iron ore bands, close to silicified shears and related quartz veins. The auriferous quartz lodes are characterised by the occurrence of visible pyrite-chalcopyrite ±pyrrhotite±sphalerite¡galena mineralisation. Gold is refractory in pyrite and chalcopyrite, but rare visible gold/electrum and telluride specks were observed in a few samples. Hydrothermal alteration includes selectively pervasive silicification, pyritisation, sericitisation, carbonatisation that are confined to a delicate set of veins and altered shears, and a more widespread propylitic alteration assemblage (quartz+|| chlorite+pyrite+calcite± epidote). The predominance of hydrated silicate phases (i.e. chlorite and sericite) within and adjacent to the shear zones points toward fixation of H2O during the shear zone development, while CO 2 was consumed to form carbonate in halos around the chloritedominated zones, leading to variations in the H2O/CO 2 ratio of the ore fluid with progression of the hydrothermal alteration. Ore textures, including hydrothermal quartz intimately associated with replacement of magnetite by pyrite, suggest the introduction of ore fluids via epigenetic conduits into the ironrich wallrocks. Fluid inclusion textural and microthermometric studies indicate heterogeneous trapping of a low-salinity (1.4-6.7 wt-% eq. NaCl) aqueous solution that coexisted with a carbonic fluid. Evidence for fluid immiscibility during ore formation includes variable liquid/vapour ratios in inclusions along individual trails and bulk inclusion homogenisation into liquid and occasionally to vapour at comparable temperatures. The trapping conditions of intragranular aqueous-carbonic inclusions approximate 264-378°C at 700-1300 bar. Similar temperature estimates have been obtained from Al-in-chlorite geothermometry of chlorite associated with sulphides in the mineralised quartz veins. Fracturing enhanced fluid circulation through the wallrock and related BIF, allowing reaction of the S-bearing ore fluid with iron oxides. This caused formation of pyrite, a rise in Eh and concomitant Au precipitation, which was enhanced by fluid immiscibility as H2S partitioned preferentially into the carbonic phase. The ore fluids have probably originated from felsite intrusions, whereas Abu Marawat gold deposit and the post-Hammamat felsites is assumed in view of their communal relationship with the N-S fault/shear trend and high geothermal gradient calculated from the fluid inclusion data. © 2009 Institute of Materials, Minerals and Mining and The AusIMM.
AUTHOR KEYWORDS: Abu marawat;  BIF;  Eastern desert;  Egypt;  Gold mineralisation;  Shear zone
DOCUMENT TYPE: Article
SOURCE: Scopus

Benham, A.J.a , Kováč, P.b , Petterson, M.G.a , Rojkovic, I.c , Styles, M.T.a , Gunn, A.G.a , Mckervey, J.A.a , Wasy, A.d 
Chromite and PGE in the logar ophiolite complex, Afghanistan
(2009) Transactions of the Institutions of Mining and Metallurgy, Section B: Applied Earth Science, 118 (2), pp. 45-58. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350241640&partnerID=40&md5=aa278d8dc017f4c0e95a0770b2ade232
AFFILIATIONS: British Geological Survey, Keyworth, Nottingham NG 12 5GG, United Kingdom; 
GET Limited, Partizanska cesta 3, 974 01 Banska Bystrica, Slovakia; 
Geological Institute Slovak Academy of Sciences, Dúbravska cesta 9, 840 06 Bratislava, Slovakia; 
Afghanistan Geological Survey, Kabul, Afghanistan
ABSTRACT: The Logar Ophiolite Complex (LOC) is located 30 km south of Kabul, Afghanistan, and extends over approximately 2000 km2. It comprises a lower lherzolitic-dunitic-harzburgitic-gabbro ultramafic-mafic unit that passes upwards into a dolerite dyke complex, basaltic pillow lavas and an uppermost sequence of volcaniclastic- and terrigenous-dominated sedimentary units. The ophiolite represents an obducted remnant of intra-Tethyan basin oceanic crust, thrust onto a platform-style cover component of the Kabul Terrane during the Himalayan orogeny. Platinumgroup minerals have been detected for the first time in chromitites and ultramafic units from the LOC. Two distinct types of chromitites and ultramafic lithologies with different origins have also been identified in this study. The first type is a low Cr, PGE-poor chromitite interpreted to have been produced in a mid ocean ridge (MOR) environment. The second type is a high Cr, relatively PGE-rich dunite and peridotite from a boninitic magma produced in a supra-subduction zone (SSZ) setting. Platinum group element (PGE) abundances in these chromitites average 12 ppb and 26 ppb for PtzPdzRh for the dunite and peridotite. Chondrite-normalised PGE patterns have two distinct trends: (a) the MOR rocks have a positive Ru anomaly with a negative Pt anomaly and a generally negative slope; and (b) the SSZ rocks show weak positive Ru and Pt anomalies and a positive slope. It is concluded that the negative sloping pattern is typical of PGE in most ophiolites elsewhere. In contrast, the positively sloping pattern is more unusual and may indicate PGE remobilisation and enrichment. © 2009 Copyright of the content and all rights therein of the contents are retained by BGS/NERC.
AUTHOR KEYWORDS: Afghanistan;  Chromite;  Ophiolite;  PGE;  Platinum
DOCUMENT TYPE: Article
SOURCE: Scopus

Opluštil, S.a , Pšenička, J.b , Libertín, M.c , Bashforth, A.R.d , Šimůnek, Z.e , Drábková, J.e , Dašková, J.f 
A Middle Pennsylvanian (Bolsovian) peat-forming forest preserved in situ in volcanic ash of the Whetstone Horizon in the Radnice Basin, Czech Republic
(2009) Review of Palaeobotany and Palynology, 155 (3-4), pp. 234-274. Cited 11 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67749086835&partnerID=40&md5=894be8fd8fd5830708cee8be89eba60a
AFFILIATIONS: Charles University in Prague, Faculty of Sciences, Albertov 6, 128 43 Praha 2, Czech Republic; 
Palaeontology Department, West Bohemian Museum in Plzeň, Kopeckého sady 2, 301 36 Plzeň, Czech Republic; 
National Museum, Vaclavske namesti 68, 115 79 Praha 1, Czech Republic; 
Department of Earth Sciences, Dalhousie University, Halifax, NS B3H 3J5, Canada; 
Czech Geological Survey, Klárov 131/3, 118 21 Praha 1, Czech Republic; 
Department of Palaeobiology and Palaeoecology, Institute of Geology v.v.i., Academy of Sciences of the Czech Republic, Rozvojová 269, 165 00 Praha 6, Czech Republic
ABSTRACT: The precursory mire of the Middle Pennsylvanian (Bolsovian) Lower Radnice Coal was buried in situ by volcanic ash, preserving the taxonomic composition, spatial distribution, vertical stratification, and synecology of this peat-forming ecosystem in extraordinary detail. Plant fossil remains represent the pre-eruption vegetation of the swamp, which resulted from accumulation of peat in a high-ash, planar (rheotrophic) mire situated in a narrow palaeovalley containing an active fluvial system. A tuff bed (the Bělka) at the base of the volcaniclastic Whetstone Horizon was exposed in two contiguous excavations over an area of 50 m2 in the Radnice Basin of western Bohemia, Czech Republic. Twenty-seven morphotaxa were identified, representing 20 whole-plant species with a wide variety of growth forms. The canopy of the peat-forming community was dominated by Cordaites borassifolius trees together with the arborescent lycopsid "Lepidodendron" (= Paralycopodites), whereas Lepidophloios cf. acerosus was subdominant. Evidence suggests that the laterally extensive "crowns" of these arborescent lycopsids would have overlapped during the final phase of their life cycles, but differences in the height of tree species resulted in a complex and vertically variable canopy interrupted by randomly distributed gaps. The understorey was dominated by medullosan pteridosperms and marattialean tree ferns, whereas zygopterid ferns and sphenophylls comprised the bulk of the ground cover. In comparison with the canopy, understorey and ground cover species were less abundant and patchier in distribution, with almost complete absence beneath the deep shade of C. borassifolius trees. Lianas that entwined arborescent trees were an important component of the peat-forming forest. Three lyginopterid pteridosperm species along with a sphenophyll had a lianescent habit based on their close association with upright or prone lycopsid trunks and "canopy" branches. Species richness in the swamp superficially appears low. However, considering the small area of excavation, along with the higher diversity known from the same tuff bed in the adjacent, former opencast Ovčín Mine, it appears that species richness in the forest was comparable to some of the less diverse Westphalian peat-forming swamps in the U.S.A. The Lower Radnice mire vegetation was compositionally homogeneous, but had a heterogeneous distribution with patchiness occurring at a very fine scale. The preserved plant assemblage most resembles mires dominated by medullosan pteridosperms and Paralycopodites described from upper Westphalian coal balls in the U.S.A., which were characterised by high diversity in all storeys and involved plants centred in high-ash peat-forming swamps. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: in situ;  palaeoecology;  peat-forming mires;  Pennsylvanian;  plant taphonomy;  tuff
DOCUMENT TYPE: Article
SOURCE: Scopus

Puga-BernabéU, Á.a  b , Vonk, A.J.a  b , Nelson, C.S.a , Kamp, P.J.J.a 
Mangarara Formation: Exhumed remnants of a middle Miocene, temperate carbonate, submarine channel-fan system on the eastern margin of taranaki Basin, New Zealand
(2009) New Zealand Journal of Geology and Geophysics, 52 (2), pp. 73-93. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70249108518&partnerID=40&md5=67f9b45d530a48f5fd54d8b0533b5754
AFFILIATIONS: Department of Earth and Ocean Sciences University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand; 
Departamento de Estratigrafía y Paleontologia, Facultad de Ciencias, Universidad de Granada, 18002 Granada, Spain
ABSTRACT: The middle Miocene Mangarara Formation is a thin (1-60 m), laterally discontinuous unit of moderately to highly calcareous (40-90%) facies of sandy to pure limestone, bioclastic sandstone, and conglomerate that crops out in a few valleys in North Taranaki across the transition from King Country Basin into offshore Taranaki Basin. The unit occurs within hemipelagic (slope) mudstone of Manganui Formation, is stratigraphically associated with redeposited sandstone of Moki Formation, and is overlain by redeposited volcaniclastic sandstone of Mohakatino Formation. The calcareous facies of the Mangarara Formation are interpreted to be mainly mass-emplaced deposits having channelised and sheet-like geometries, sedimentary structures supportive of redeposition, mixed environment fossil associations, and stratigraphic enclosure within bathyal mudrocks and flysch. The carbonate component of the deposits consists mainly of bivalves, larger benthic foraminifers (especially Amphistegina), coralline red algae including rhodoliths {Lithothamnion and Mesophyllum), and bryozoans, a warm-temperate, shallow marine skeletal association. While sediment derivation was partly from an eastern contemporary shelf, the bulk of the skeletal carbonate is inferred to have been sourced from shoal carbonate factories around and upon isolated basement highs (Patea-Tongaporutu High) to the south. The Mangarara sediments were redeposited within slope gullies and broad open submarine channels and lobes in the vicinity of the channel-lobe transition zone of a submarine fan system. Different phases of sediment transport and deposition (lateral-accretion and aggradation stages) are identified in the channel infilling. Dual fan systems likely co-existed, one dominating and predominantly siliciclastic in nature (Moki Formation), and the other infrequent and involving the temperate calcareous deposits of Mangarara Formation. The Mangarara Formation is an outcrop analogue for middle Miocene-age carbonate slope-fan deposits elsewhere in subsurface Taranaki Basin, New Zealand. © The Royal Society of New Zealand 2009.
AUTHOR KEYWORDS: Mangarara Formation;  Middle Miocene;  Sediment gravity flows;  Submarine channel;  Taranaki Basin;  Temperate carbonates
DOCUMENT TYPE: Article
SOURCE: Scopus

Németh, K.a , Budai, T.b 
Diatremes cut through the Triassic carbonate platforms in the Dolomites? Evidences from and around the Latemar, northern Italy
(2009) Episodes, 32 (2), pp. 74-83. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349766939&partnerID=40&md5=8bc668615d90b48f2af1dd3b162ed4e9
AFFILIATIONS: Institute of Natural Resources, Volcanic Risk Solutions, Massey University, Palmerston North, New Zealand; 
Department of Geological Research, Geological Institute of Hungary, Stefánia út 14, Budapest, H-l 143, Hungary
ABSTRACT: Widespread volcanism associated with Middle Triassic carbonate platforms is well known, and in many cases referred as a partial cause of the disruption of platform development due to burial by volcanic material. It is no doubt that silicic explosive volcanism produced large volume of volcanic material accumulated in basins surrounding the carbonate platforms (Buchenstein basins) alternating with pelagic carbonates of basin facies. There are large numbers of mafic eruptive products associated with individual carbonate platforms such as the Latemar in the Dolomites in northern Italy. These eruptive products are dominated by mafic dyke swarms which due to their more erodable nature provide a characteristic castle-like architecture of the present day edifice, having altered mafic dyke material eroded away between more resistant limestone and dolomite pillars. Here we present field evidences to demonstrate that there are characteristic zones of volcaniclastic vertical breccia horizons more consistent with diatreme origin. In many occasions, such volcanic breccia pipes and associated tilted blocks were used for demonstrating the casual relationship between tectonic event-generated collapsed carbonate platform units and accumulation of volcanic material in the resulting basins. Here we concur with this idea, and provide field evidences that such volcanic breccia pipes are rather exposed volcanic conduits, resulted from magma and water interaction driven diatreme formation. This finding from the Latemar in northern Italy highlights the need of revision of the cause and consequences of different types of volcanism in the final episodes of the carbonate platform evolution in the Triassic of the Tethys.
DOCUMENT TYPE: Article
SOURCE: Scopus

Zhao, Y., Morzadec-Kerfourn, M.-T.
Dinoflagellate cysts and quaternary paleoenvironment in the Izu-Bonin region, North-West Pacific (ODP leg 125, site 782A and leg 126, site 791B) [Kystes de dinoflagellés et paléoenvironnement quaternaire dans la région izu-bonin, nord-ouest pacifique (ODP leg 125, site 782A et leg 126, site 791B)]
(2009) Quaternaire, 20 (2), pp. 195-213. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-69249181346&partnerID=40&md5=4d55aeb9b540175e00201b3a38fcdbd6
ABSTRACT: Fifty species of dinoflagellate cysts, among them two new species, have been identified in oceanic sediments of the Izu-Bonin region, south of Japan. All these species have a paleoenvironmental significance. The Quaternary climatic oscillation and environment evolution in the NW Pacific have been demonstrated by the variation of dinoflagellate cyst assemblages and the contents pollen grains in the arc sediments of the Izu-Bonin region. The variation of species ratios: temperate-warm to temperate-cold dinoflagellate cysts reveals the cyclic temperature changes of sea surface waters. The data are used to reconstruct the climatic evolution since 1,79 Ma ago. The results of the present study and a consideration of relevant sedimentological factors allow us to draw the following conclusions concerning the environment of the lzu-Bonin region. It appears that the carbonate concentration in sediments was higher in the temperate-cold than in the temperate-warm phases. In comparison with the ridge of outer arc, the axial region of the inner arc rift is characterized by greater proportion of volcaniclastic materials as well as a higher sedimentation rate and the palynological contents by high percentages of coniferous pollen. These particularity suggest a possible effect of the volcanic activity on the palynological contents in the intra-arc basin since 1 Ma ago. Thus the axial region of the inner arc has maintained outside of the influence of warm current Kuroshio since 0.46 Ma ago; this is reflected by the very high abundance of Impagidinium patulum to Impagidinium aculeatum.
AUTHOR KEYWORDS: Deep sea sediments;  Dinoflagellate cysts;  Izu-Bonin region;  North-West Pacific ocean;  Odp leg125 and 126;  Quaternary
DOCUMENT TYPE: Article
SOURCE: Scopus

Constantina, C.a , Szakács, A.b , Pécskay, Z.c 
Petrography, geochemistry and age of volcanic rocks in the gurasada area, southern Apuseni Mts
(2009) Carpathian Journal of Earth and Environmental Sciences, 4 (1), pp. 31-47. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-65749090376&partnerID=40&md5=fa3dcaea4790de4eadecd2075f1b259c
AFFILIATIONS: North University of Baia Mare, 62A Dr. V. Babes Street, 430083 Baia Mare, Romania; 
Sapientia University, 400112 Cluj-Napoca, Romania; 
Institute of Nuclear Research, Hungarian Academy of Sciences, H-4026 Debrecen, Hungary
ABSTRACT: This paper proves for the first time the existence of a complex distribution of volcanic rock types occurring in the Gurasada region. At the base of these a bentonite deposit crops out in the Gurasada open pit, followed by pyroclastic deposits represented by pyroclastic breccia and rare tuff levels the youngest rocks are lava flows exposed in the Runcşor Hill. Thermometamorphic products represented by hornfels are described here for the first time within the outcrop area of the pyroclastic breccia. The site observations, petrographic, XRD, RAMAN spectroscopy and chemical analyses indicated the formation of the bentonite deposit by weathering of a vitroclastic tuff, probably of dacitic composition, belonging to a first (more felsic) eruptive stage consisting of Plinian-type explosive volcanism. The pyroclastic breccia, tuffs and lava flows are mainly of calc-alkaline andesitic composition and belong to a second stage of volcanism, which developed intermittently, over a longer period of time. Radiometric dating (K/Ar method) of the rocks indicates the formation of the volcanic-volcaniclastic deposits within a period of 69 to 80 million years ago. These ages confirm that these volcanics belong to the laramic cycle as inferred previously place them at the level of Upper Cretaceous (Senonian).
AUTHOR KEYWORDS: Andesite;  Bentonite;  Laramian;  Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Rice, S.P.a , Robertson, A.H.F.b , Ustaömer, T.c , Inan, N.d , Tasli, K.d 
Late cretaceous-early eocene tectonic development of the tethyan suture zone in the erzincan area, Eastern Pontides, Turkey
(2009) Geological Magazine, 146 (4), pp. 567-590. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349402252&partnerID=40&md5=e3734aababd3342bf9a51f2205b10b54
AFFILIATIONS: CASP, Department of Earth Sciences, University of Cambridge, 181a Huntingdon Road, Cambridge CB3 0DH, United Kingdom; 
School of GeoSciences, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 3JW, United Kingdom; 
Department of Geology, Istanbul University, Avcilar 34850 Istanbul, Turkey; 
Mersin Üniversitesi, Jeoloji Mühendisliǧi Bölümü, 33342 Çiftlikköy, Mersin, Turkey
ABSTRACT: Six individual tectonostratigraphic units are identified within the Izmir-Ankara-Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayikayasi Formation of Campanian-Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayikayasi Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of ∼75% (by volume) serpentinized peridotite (mainly harzburgite), ∼20% diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Mélange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadaǧ Formation, of Campanian-Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian-Early Eocene Sütpinar Formation (∼1500 m thick) is a coarsening-upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene-Eocene Sipikör Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic arc units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian-Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys. Copyright © Cambridge University Press 2009.
AUTHOR KEYWORDS: Pontides;  Stratigraphy;  Suture zone;  Tethys;  Turkey
DOCUMENT TYPE: Article
SOURCE: Scopus

Porreca, M.b , Mattei, M.b , Di Vincenzo, G.a 
Post-deformational growth of late diagenetic greigite in lacustrine sediments from southern Italy
(2009) Geophysical Research Letters, 36 (9), art. no. L09307, . Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68249139920&partnerID=40&md5=fe27ae3b9d76fa6a41eeeccc953e4a5f
AFFILIATIONS: Istituto di Geoscienze e Georisorse, CNR, via Moruzzi 1, 1-56124 Pisa, Italy; 
Dipartimento Scienze Geologiche, Universita Roma Tre, Largo S. L. Murialdo 1, 1-00146 Roma, Italy
ABSTRACT: Paleomagnetic, rock magnetic and micro-textural analyses from a Middle Pleistocene lacustrine sequence in the southern Apennines (Italy) indicate the presence of greigite and magnetite as the main magnetic minerals at different stratigraphie levels. In all cases a normal polarity characteristic remanent magnetization (ChRM) was observed, in agreement with an 40Ar- 39Ar age of 0.712 ± 0.018 Ma from volcaniclastic sanidine. After correction for bedding tilt, ChRM directions carried by greigite do not coincide with the expected geocentric axial dipóle field direction at the site latitude, whereas the magnetite ChRMs directions do. The data indicate that the greigite magnetization was acquired after tilting and after lock-in of the magnetite ChRM. The estimated delay for the remanence carried by greigite with respect to deposition is ∼300 ka. Scanning electron microscope analyses indicate that alteration of detrital volcanic minerals has occurred and that authigenic greigite is generally present in agglomerates and around volcanic grains. This observation is consistent with a late diagenetic origin of greigite due to anoxic conditions and availability of dissolved sulfide associated with decomposition of organic matter in the paleolake. Documentation of a late diagenetic magnetization confirms that care should be taken when using greigite-bearing sediments for magnetostratigraphic and tectonic studies. Copyright 2009 by the American Geophysical Union.
DOCUMENT TYPE: Article
SOURCE: Scopus

Sierra, S., Moreno, C., Pascual, E.
Stratigraphy, petrography and dispersion of the lower Permian syn-eruptive deposits in the Viar Basin, Spain
(2009) Sedimentary Geology, 217 (1-4), pp. 1-29. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67349203817&partnerID=40&md5=74a7c94730249118b8665cedec45a5ea
AFFILIATIONS: Depto. Geología, Facultad de Ciencias Experimentales, Univ. Huelva, Campus El Carmen, Avda. 3, Marzo s/n, Huelva, Spain
ABSTRACT: This paper presents a stratigraphic, petrographic and sedimentologic analysis of felsic syn-eruptive deposits of the southernmost Permian basin in Europe (Viar Basin), an inner-orogenic, transtensional half-graben located between two major geotectonic zones of the Iberian Variscan Belt, SW Spain. The syn-eruptive deposits of the Viar Basin represent a mappable lithostratigraphic unit, that is herein named the Los Canchales Formation. This unit forms a wedge-shaped body bounded by alluvial-fluvial deposits (red layers) that are in gradational contact. The stratigraphic architecture of the Los Canchales Formation is complex with frequent facies changes and interfingering among pyroclastic rocks, resedimented-volcaniclastic rocks and sedimentary rocks. Abundant fossil flora is also recorded. A wax-wane cycle of volcanic activity is recognized during the syn-eruptive period. Two short-lived volcanic episodes were recorded including ignimbrites and a possible phreatomagmatic event. Explosive volcanism generated pyroclastic flow, surge and ash-fall deposits, in cases collapsing the drainage network. They also modified the vegetation and created a new depositional setting with four successive sedimentary environments: vegetated floodplain, ephemeral sandy braidplain, palustrine environment and again vegetated floodplain. Input of pyroclasts followed a NW to SE longitudinal-axial dispersal pattern. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Permian;  Resedimented volcanic deposits;  Spain;  Syn-eruptive deposits;  Viar Basin
DOCUMENT TYPE: Article
SOURCE: Scopus

Clague, D.A.
Accumulation rates of volcaniclastic deposits on Loihi Seamount, Hawaii
(2009) Bulletin of Volcanology, 71 (6), pp. 705-710. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68349114952&partnerID=40&md5=db117c8b4193d31b43e634a7d2bab488
AFFILIATIONS: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
ABSTRACT: AMS radiocarbon age dating of planktonic foraminifera in volcaniclastic deposits on Loihi Seamount yields ages ranging from 590 years before present (y BP) at 10 cm depth to 5,880 y BP at 1,007 cm depth in an 11-m-thick section exposed along inward facing, caldera-bounding faults on the eastern side of Loihi's summit. The accumulation rate of the deposit was about 0.37 cm/y from 5,880 to 3,300 y BP and it consisted of subequal amounts of alkalic and tholeiitic fragments. The rate slowed dramatically at about 3,300 y BP to an average 0.04 cm/y and the particles that have accumulated since consist mostly of alkalic glass fragments. The decrease in accumulation rate could indicate a decrease in volcanic activity at Loihi beginning about 3,300 y BP. This lower level of activity appears to be continuing today. © Springer-Verlag 2009.
AUTHOR KEYWORDS: AMS radiocarbon ages;  Hawaiian volcanism;  Loihi Seamount;  Volcaniclastic deposits
DOCUMENT TYPE: Article
SOURCE: Scopus

Srichan, W., Crawford, A.J., Berry, R.F.
Geochemistry and geochronology of Late Triassic volcanic rocks in the Chiang Khong region, northern Thailand
(2009) Island Arc, 18 (1), pp. 32-51. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-65449150186&partnerID=40&md5=9647f4214ff65ab34211c68ee2ede463
AFFILIATIONS: CODES ARC Centre of Excellence in Ore Deposits, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia
ABSTRACT: The Chiang Khong segment of the Chiang Khong-Lampang-Tak Volcanic Belt is composed of three broadly meridional sub-belts of mafic to felsic volcanic, volcaniclastic, and associated intrusive rocks. Associated sedimentary rocks are largely non-marine red beds and conglomerates. Three representative Chiang Khong lavas have Late Triassic (223-220 Ma) laser ablation inductively coupled mass-spectroscopy U-Pb zircon ages. Felsic-dominated sequences in the Chiang Khong Western and Central Sub-belts are high-K calc-alkaline rocks that range from basaltic to dominant felsic lavas with rare mafic dykes. The Western Sub-belt lavas have slightly lower high field strength element contents at all fractionation levels than equivalent rocks from the Central Sub-belt. In contrast, the Eastern Sub-belt is dominated by mafic lavas and dykes with compositions transitional between E-mid-oceanic ridge basalt and back-arc basin basalts. The Eastern Sub-belt rocks have higher FeO* and TiO2 and less light rare earth element enrichment than basalts in the high-K sequences. Basaltic and doleritic dykes in the Western and Central sub-belts match the composition of the Eastern Sub-belt lavas and dykes. A recent geochemical study of the Chiang Khong rocks concluded that they were erupted in a continental margin volcanic arc setting. However, based on the dominance of felsic lavas and the mainly non-marine associated sediments, we propose an alternative origin, in a post-collisional extensional setting. A major late Middle to early Late Triassic collisional orogenic event is well documented in northern Thailand and Yunnan. We believe that the paucity of radiometric dates for arc-like lavas in the Chiang Khong-Lampang-Tak Volcanic Belt that precede this orogenic event, coupled with the geochemistry of the Chiang Khong rocks, and strong compositional analogies with other post-collisional magmatic suites, are features that are more typical of volcanic belts formed in a rapidly evolving post-collisional, basin-and range-type extensional setting. © 2009 The Authors Journal compilation © 2009 Blackwell Publishing Asia Pty Ltd.
AUTHOR KEYWORDS: Chiang Khong-Lampang-Tak Volcanic Belt;  Late Triassic volcanic rocks;  Post-collisional magmatism;  Thailand tectonics
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

Duuring, P.a  c , Rowins, S.M.a , McKinley, B.S.M.a , Dickinson, J.M.a , Diakow, L.J.b , Kim, Y.-S.c , Creaser, R.A.d 
Magmatic and structural controls on porphyry-style Cu-Au-Mo mineralization at Kemess South, Toodoggone District of British Columbia, Canada
(2009) Mineralium Deposita, 44 (4), pp. 435-462. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-65349172953&partnerID=40&md5=756f2d66bbe4e519944170eb8475edcf
AFFILIATIONS: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4, Canada; 
British Columbia Geological Survey, Ministry of Energy, Mines and Petroleum Resources, Victoria, BC V8V 1X4, Canada; 
Department of Environmental Geosciences, Pukyong National University, Busan 608-737, South Korea; 
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada
ABSTRACT: Kemess South is the only Cu-Au-Mo mine in the Toodoggone district and a major Cu and Au producer in British Columbia. Porphyry-style Cu-Au-Mo mineralization is mainly hosted by the tabular, SW-plunging, 199.6±0.6-Ma Maple Leaf granodiorite, which intrudes tightly folded, SW-dipping, Permian Asitka Group siltstone and limestone and homogeneous Triassic Takla Group basalt. Southwest-dipping 194.0±0.4-Ma Toodoggone Formation conglomerate, volcaniclastic, and epiclastic rocks overlie the granodiorite and Asitka Group rocks. Minor Cu-Au-Mo mineralization is hosted by the immediate Takla Group basalt country rock, whereas low-tonnage high-grade Cu zones occur beneath a 30-m-thick leached capping in supergene-altered granodiorite and in exotic positions in overlying Toodoggone Formation conglomerate. Granodiorite has an intrusive contact with mineralized and altered Takla Group basalt but displays a sheared contact with unmineralized and less altered Asitka Group siltstone. The North Block fault is a deposit-scale, E-striking, steeply S-dipping normal fault that juxtaposes the granodiorite/basalt ore body against unmineralized Asitka Group rocks. Younger NW- and NE-striking normal-dextral faults cut all rock types, orebodies, and the North Block fault with displacements of up to 100 m and result in the graben-and-horst-style block faulting of the stratigraphy and ore body. Both basalt and granodiorite host comparable vein sequence and alteration histories, with minor variations in hydrothermal mineral assemblages caused by differing protolith chemistry. Early potassic alteration (and associated early-stage Cu ± Au ± Mo mineralization) is partly replaced by phyllic and intermediate argillic alteration associated with main-stage Cu - Au - Mo mineralization. Two main-stage veins have Re-Os molybdenite ages of 201.3±1.2 and 201.1±1.2 Ma. These mineralization ages overlap the 199.6±0.6-Ma U-Pb zircon crystallization age for the Maple Leaf granodiorite. Late-stage pyrite-rich stringer veins and related phyllic alteration assemblages are cut by anhydrite-rich, carbonate-rich, and chlorite veins. Fluids and metals associated with early-, main-, and late-stage veins were probably derived principally from the same deep magma chamber as the Maple Leaf granodiorite. These magmatic-derived fluids interacted with Asitka and Takla Group country rocks and possibly with meteoric and metamorphic fluids prior to mineralization. © Springer-Verlag 2009.
AUTHOR KEYWORDS: Copper;  Gold;  Kemess South;  Porphyry;  Stikine;  Toodoggone
DOCUMENT TYPE: Article
SOURCE: Scopus

Berger, A., Gier, S., Krois, P.
Porosity-preserving chlorite cements in shallow-marine volcaniclastic sandstones: Evidence from cretaceous sandstones of the sawan gas field, Pakistan
(2009) AAPG Bulletin, 93 (5), pp. 595-615. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649772125&partnerID=40&md5=bb1d75e6a8f160162ccd268e3fbd9b99
AFFILIATIONS: Department of Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
ABSTRACT: Sandstones that have high porosity and permeability at great burial depth and high temperatures are of economic importance because a significant amount of hydrocarbons have been discovered in such reservoirs. The Sawan gas field, with an expected ultimate recovery of more than 1 tcf, lies in the middle Indus Basin. The reservoir rocks, Cretaceous volcani-clastic sandstones of the lower Goru Formation, show very high porosities at a reservoir temperature of 175°C and depths of 3000 to 3500 m (9842 to 11,483 ft). The sandstones are mostly feldspathic litharenites. Strongly altered volcanic rock fragments are the most important lithic component. The clay fraction consists of Fe-rich chlorite (chamosite) and illite. Diagenetic features such as compaction, quartz overgrowths, carbonate cements, and feldspar dissolution are observed. The most distinguishing feature is a double layer of authigenic chlorite, lining the pores of the sandstones. Chlorite additionally occurs as a pore-filling cement and as chlo-ritized detrital components, all having similar chemical composition. The pore-lining cement clearly developed in two stages: an earlier, poorly crystallized, and a later, better crystallized growth. Missing rims at grain contacts show that precipitation occurred after an initial stage of compaction but early relative to other diagenetic phases. Both chlorite rims grew by direct precipitation from pore waters, using products derived from volcanic rock fragments. In areas with no, thin, or discontinuous chlorite rims, quartz cementation is common. Well-developed chlorite rims inhibited quartz cementation, preserved porosities of up to 20%, and good permeabilities. Porosity-preserving chlorite cementation in Sawan is restricted to sediments of a shallow-marine environment. ©2009. The American Association of Petroleum Geologists.
DOCUMENT TYPE: Article
SOURCE: Scopus

De Haller, A.a  b , LluíFontbotéc 
The raucl-condestable iron oxide copper-gold deposit, central coast of peru: Ore and related hydrothermal alteration, sulfur isotopes, and thermodynamic constraints
(2009) Economic Geology, 104 (3), pp. 365-384. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649968035&partnerID=40&md5=2873c07aaa40c8ecea521639b456c5b9
AFFILIATIONS: University of Geneva, Mineralogy Department, rue des Maraichers 13, CH-1205 Genéve, Switzerland; 
University of Bern, Institute of Geological Sciences, RWI Group, Baltzcrstrasse 1-3, CH-3012 Bern, Switzerland; 
University of Geneva, Mineralogy Department, rue des Maraichers 13, CH-1205 Geneve, Switzerland
ABSTRACT: The iron oxide copper-gold (IOCG) Raúl-Condestable deposit is located 90 km south of Lima, Peru, and approximately 5 km from the Pacific coast. Mineralization consists mainly of replacement mantos and disseminations within permeable volcaniclastic and carbonate-rich rocks and structurally controlled veins surrounding a coeval and apparently causative intrusion of tonalitic composition emplaced in the core of a dacitic volcano. Potassic (biotite grading upward to sericite-chlorite) alteration and a poorly developed, almost sulfide-free, quartz stockwork closely border the tonalite, affecting the basaltic to dacitic Lower Cretaceous volcano-sedimentary host sequence. Ore is associated with a hydrated calc-silicate (mainly amphiboles) alteration that surrounds the biotite alteration. A hematite-chlorite (albite, epidote, calcite) alteration affects the periphery of the system. The main ore stage is characterized by two end-member mineral associations that were formed according to (1) an oxidized deposition sequence (hematite-magnetite-pyrite-chalcopyrite) occurring in and near feeder structures, and (2) a reduced deposition sequence (pyTrhotite-pyrite-chalcopyrite) found in volcaniclastic rocks and veins. Early specular hematite of the oxidized sequence is transformed to magnetite ("mushke- tovite"). The main ore-stage mineralization is cut by minor late-stage calcite-sulfide veins. Main ore-stage sulfides have 63IS values asymmetrically distributed from 1.0 to 26.3 per mil, with a median at 6.6 per mil (n = 51). Similar values are observed for pyrrhotite, pyrite, and chalcopyrite. The δ34S values depend on the stratigraphic position, with deep-seated vein samples normally distributed between 1.0 and 6.3 per mil (avg about 3.5%o, n = 13) and shallower samples from 2.7 to 26.3 per mil (median around 7.5%o, n = 39). Sulfides found in late-stage calcite-sulfide veins show strongly negative o^S values ranging between -32.7 and -22.9 per mil (n = 6), indicating a possible biogenic source. Because no rock unit is known to occur in the internal parts of the deposit that could have oxidized fluids to the point of hematite stability, the oxidized mineral sequence is best explained by magmatic brines following the SO2-H2S gas buffer at high temperature (&gt;350°C) and fluid/rock ratio. This is supported by the close to magmatic δ34S values of sulfides from the deep parts of feeder veins. Mass-balance calculation based on sulfur isotope data suggests that at the deposit scale, the bulk of the sulfides is dominated by magmatic sulfur, with sulfides of the oxidized minerals association having a larger component of magmatic sulfur than those of the reduced mineral association. The deposition sequence from hematite to chalcopyrite reflects the cooling of the magmatic fluid and redox and pH buffering by the basaltic-andesitic volcano-sedimentary host rocks. Thus, the occurrence of magnetite pseudomorphous after early hematite (mushketovite) paragenetically followed by iron-bearing sulfides is interpreted to be direct field evidence for precipitation from oxidized magmatic brines. The same sequence has been described in many IOCG, skarn, and some porphyry copper deposits worldwide. δ34S values of sulfides ranging up to 26.3 per mil are found in what corresponded to a relatively shallow aquifer filled with evolved reduced seawater. Heavy sulfur in H2S was produced through thermochemical reduction of Aptian seawater sulfate (δ34S = 14%o) in the recharge zone, which is interpreted to correspond to the hematite- clilorite (albite, epidote, calcite) alteration present at the upper flanks of the hydrothennal system, adjacent to the causative intrusion. Hematitization (through oxidation) resulted from the highfo2 of seawater and from the reduction of its sulfate to H 2S by the Fe2+ contained in the rock. In the core of the system, the seawater-derived fluids reached near chemical equilibrium with their actinolitized host rock, at about 300° to 350°C, in reduced, rock-dominated conditions. Mixing of these fluids with magmatic brines, already partially or totally reduced through reaction with wall rock at medium to low magmatic fluid/rock ratio can explain the large positive δ34S scatter observed in sulfides of the reduced mineral association, at stratigraphically shallow positions. © 2009 Society of Economices Geologists, Inc.
DOCUMENT TYPE: Article
SOURCE: Scopus

Korn, D.a , Kaufmann, B.b 
A high-resolution relative time scale for the Viséan stage (Carboniferous) of the Kulm Basin (Rhenish Mountains, Germany)
(2009) Geological Journal, 44 (3), pp. 306-321. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69849105694&partnerID=40&md5=819c9cc42bc71c98bb0275640c253e6e
AFFILIATIONS: Museum für Naturkunde der Humboldt-Universitat zu Berlin, Berlin, Germany; 
Ö sterreichische Akademie der Wissenschaften, Kommission für die palaontologische und stratigraphische Erforschung Österreichs, C/o Institut Erdwissenschaften (Geologie und Palaontologie) Karl-Franzens-Univ. Graz, Graz, Austria
ABSTRACT: The Viséan (Carboniferous) sedimentary succession of the basinal Kulm facies (Rhenish Mountains) was investigated in detail in order to achieve a high-resolution stratigraphic subdivision and correlation. Additionally, the ranges of fossil index taxa (ammonoids), fossil marker beds, volcaniclastic horizons and sedimentary features (e.g. colour changes) were integrated in the correlation. As a result, a comprehensive database was compiled, which contains 190 stratigraphic events of the Viséan interval of this area. Several sections are almost completely composed of shales, which are regarded to represent a slow but constant basinal background sedimentation of the Kulm facies. The thickness of lithological homogeneous sections thus indicates an approximately linear record of time and the average thicknesses of biozones and positions of stratigraphic events can easily be calculated from the compiled database. The result is an approximately time-linear biostratigraphic scale for the Visé an Stage of the Kulm Basin. Given a numerical length of the Visé an Stage of ca. 19 Ma, 190 stratigraphic events give a mean resolution of 100000 years. This is unique in Palaeozoic stratigraphy. © 2008 John Wiley & Sons, Ltd.
AUTHOR KEYWORDS: Ammonoids;  Carboniferous;  Chronostratigraphy;  Index horizons;  Time scale;  Volcaniclastics
DOCUMENT TYPE: Article
SOURCE: Scopus

Mrlina, J.a , Kämpf, H.b , Kroner, C.b , Mingram, J.b , Stebich, M.c , Brauer, A.b , Geissler, W.H.d , Kallmeyer, J.b  f , Matthes, H.e , Seidl, M.a 
Discovery of the first Quaternary maar in the Bohemian Massif, Central Europe, based on combined geophysical and geological surveys
(2009) Journal of Volcanology and Geothermal Research, 182 (1-2), pp. 97-112. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-64149113281&partnerID=40&md5=5d7e9e11bcf89999f349df01065de791
AFFILIATIONS: Institute of Geophysics ASCR, Boční II/1401, 14131 Prague 4, Czech Republic; 
Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, D-14473 Potsdam, Germany; 
Senckenberg, Forschungsinstitute und Naturmuseum, Forschungsstation für Quartärpaläontologie, Am Jakobskirchhof 4, D-99423 Weimar, Germany; 
Alfred Wegener Institute for Polar and Marine Research, Am Alten Hafen 26, D-27568 Bremerhaven, Germany; 
Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg, D-14473 Potsdam, Germany; 
University of Potsdam, Department of Geosciences, Karl-Liebknecht-Str. 27, Haus 27, 14476 Potsdam, Germany
ABSTRACT: Based on results of previous investigations of tephra-tuff volcaniclastic deposits and a geophysical survey in the surroundings of the Železná hůrka Quaternary volcano, West Bohemia, we performed detailed geophysical surveys using gravimetry, magnetometry and electrical conductivity techniques. Striking anomalies were revealed in a morphological depression near Mýtina, West Bohemia, as a strong evidence of the assumed maar-diatreme structure. The sharp isometric gravity low of - 2.30 mGal, as well as the corresponding positive magnetic anomaly of 200 nT with a negative rim on its northern side indicate a steeply dipping geological body of low density and containing magnetic rocks/minerals. Magnetic survey also showed pronounced local anomalies outside the depression that can reflect relicts of the tephra rim of the maar. This geophysical evidence was then proven by an exploratory drilling near the centre of the gravity anomaly. Macroscopic on-site evaluation of the core, and more detailed sedimentological, petrochemical, palynological and microbiological laboratory analyses further confirmed the existence of a maar structure filled by 84 m of lake sediments reflecting a succession of several warm and cold climatic periods. Results of palynological analyses confirm the presence of a continuous palaeoclimate archive, with at least three successive warmer periods of most probably interstadial character from the upper Quaternary Saalian complex. Therefore, the recovered sediment sequence holds strong potential for in-depth paleoclimate reconstruction and deep biosphere studies. At the bottom of the Mýtina-1 (MY-1) borehole (84-85.5 m), country rock debris was found, containing also volcanic bombs and lapilli. The discovered volcanic structure is considered to be the first known Quaternary maar-diatreme volcano on the territory of the Bohemian Massif. Because of hidden active magmatic processes in combination with earthquake swarm seismicity ca. 20-30 km north of the Mýtina maar, reconstruction of the palaeovolcanological evolution is important for evaluation of hazard potential of the NE and E part of the Cheb Basin. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Eger Rift;  geophysical survey;  Quaternary maar volcanism;  Saalian lake sediments;  volcanic hazard potential
DOCUMENT TYPE: Article
SOURCE: Scopus

Leybourne, M.I.a , Cousens, B.L.b , Goodfellow, W.D.c 
Lead isotopes in ground and surface waters: Fingerprinting heavy metal sources in mineral exploration
(2009) Geochemistry: Exploration, Environment, Analysis, 9 (2), pp. 115-123. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-66549091130&partnerID=40&md5=0312a697f26c375e30f681fcc3e25435
AFFILIATIONS: GNS Science, P.O. Box 30-368, Lower Hutt, New Zealand; 
Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, Ottawa, ON K1S 5B6, Canada; 
Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada
ABSTRACT: We collected ground and surface water samples, as well as samples of host felsic and mafic volcanic lithologies and massive sulphide ore from the Restigouche deposit in the Bathurst Mining Camp, New Brunswick, Canada. These water and rock samples were analysed for their Pb isotope composition in order to investigate the utility of Pb isotope analyses of waters for mineral exploration and environmental tracing. Waters proximal to the near-surface Zn-Pb Restigouche deposit have Pb isotope compositions indistinguishable from galena from a number of volcanogenic massive sulphide deposits in the camp (206Pb/204Pb = 18.18-18.34; 207Pb/204Pb = 15.63-15.68; 208Pb/204Pb = 38.10-38.21). These deposit proximal waters are interpreted to have derived the dissolved (&lt; 0.45 μm) Pb primarily from oxidation of massive sulphide minerals (galena, sphalerite). Ground-waters more distal from the Restigouche deposit have more radiogenic isotopic compositions, with Pb derived by weathering of U- and Th-rich minerals in the felsic volcanic and volcaniclastic country rocks that host the deposit. There is no correlation between dissolved Pb concentration and isotopic signature owing to the low solubility of Pb in water. The Pb isotopic composition of the dissolved loads of waters is therefore a powerful tool in fingerprinting Pb sources and has important implications for mineral exploration and environmental baseline studies. © 2009 AAG/Geological Society of London.
AUTHOR KEYWORDS: Environmental geochemistry;  Groundwater;  Lead isotopes;  Massive sulphide;  Mineral exploration
DOCUMENT TYPE: Article
SOURCE: Scopus

Miller, N.R.a , Stern, R.J.b , Avigad, D.c , Beyth, M.d , Schilman, B.d 
Cryogenian slate-carbonate sequences of the Tambien Group, Northern Ethiopia (I): Pre-"Sturtian" chemostratigraphy and regional correlations
(2009) Precambrian Research, 170 (3-4), pp. 129-156. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-63149173106&partnerID=40&md5=8fd1b3aea683769de7e58b384072736c
AFFILIATIONS: Department of Geological Sciences, University of Texas at Austin, 1 University Station C1100, Austin, TX 78712-0254, United States; 
Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688, United States; 
Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, 91904, Israel; 
Geological Survey of Israel, Jerusalem, Jerusalem, 95501, Israel
ABSTRACT: Ethiopia's youngest Neoproterozoic sedimentary outcrops are "Sturtian" diamictites that cap the Tambien Group (Tigre, N. Ethiopia), a modestly thick (1-3 km) slate and carbonate succession that records early Cryogenian evolution of the Mozambique Ocean within the southern Arabian-Nubian Shield. Tambien carbonate deposition occurred over an island arc accretion complex, during or after the waning phase of arc magmatism (Tsaliet Group; ∼775-740 Ma) and ended prior to the structural and magmatic emergence of the East African Orogen (EAO; c. ≥630-610). Closure of the Mozambique Ocean to form the EAO, sometime after the deposition of "Sturtian" (∼715-685 Ma) diamictite and before the onset of EAO magmatism, destroyed accommodation space capable of preserving younger Cryogenian episodes. Litho- and chemostratigraphic variations of the Tambien Group, compiled from investigations of four areas of Tigre, demonstrate that integrated δ13Ccarb and 87Sr/86Sr stratigraphies are effective for regional correlation and form the basis for a composite reference section (introduced here, but evaluated in the context of evolving Cryogenian Earth systems in a companion manuscript). Sediments in the Negash synclinorium span the depositional histories of all other localities but may contain a significant unconformity, suggesting at least local structural relief differentiation during deposition of the early Tambien Group carbonate platform. Mai Kenetal synclinorium sediments may preserve this missing interval. The regional Tambien record has two consecutive positive-to-negative carbon isotope excursions, the first associated with an abrupt transition to carbonates with cap carbonate-like features (basal Assem Limestone - Mai Kenetal) and the second associated with the transition from relatively organic-rich black limestone to "Sturtian" diamictite (Negash). Sr isotope compositions rise from &lt;0.7055 in dolomites near the base of the carbonate sequence to a stratigraphic plateau near 0.7068 in upper black limestones, before declining to 0.7064 (or lower) in the transition to diamictite deposition. Sr contents of limestones increase (9x) systematically above the lower negative δ13Ccarb interval. Textural and chemical properties of the Assem Limestone and its depositional context, suggest a transgressive cap-carbonate sequence. Although conformably underlain by laminated slate without definitive evidence of glaciation, its lithostratigraphic position as the lowest significant carbonate unit correlates regionally above polymict volcaniclastic agglomerates and greywackes (Negash and Samre synclinoria) previously interpreted to have a possible glacigenic origin. Chemical weathering indices (PIA: 92-99) in thick (0.5-1.1 km) slate comprising the lower Tambien Group indicate the Tsaliet arc accretion complex underwent protracted and intensive silicate weathering prior to carbonate deposition. These findings raise the possibility that the initial negative δ13Ccarb interval of the Tambien Group corresponds to recovery from an earlier pre-"Sturtian" cooling event, perhaps related to the Kaigas glacial interval. If so, the Assem Limestone is the first and oldest cap carbonate sequence in the Arabian-Nubian Shield. The chemostratigraphic framework for the Tambien Group contributes to empirical observations that integrated C and Sr isotope stratigraphies are effective for Cryogenian (pre-"Sturtian") chemostratigraphic correlations. However, more work is required to understand how δ13Ccarb specifically relates to marine δ13CDIC. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Cryogenian;  Ethiopia;  Neoproterozoic;  Snowball Earth Hypothesis;  Sr and C isotope stratigraphy;  Sturtian
DOCUMENT TYPE: Article
SOURCE: Scopus

Sheth, H.C.a , Ray, J.S.b , Bhutani, R.c , Kumar, A.b , Smitha, R.S.c 
Volcanology and eruptive styles of Barren Island: An active mafic stratovolcano in the andaman sea, NE Indian Ocean
(2009) Bulletin of Volcanology, 71 (9), pp. 1021-1039. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350366395&partnerID=40&md5=24d33b02741054c135c50ba60ba0a360
AFFILIATIONS: Department of Earth Sciences, Indian Institute of Technology Bombay (IITB), Powai, Mumbai 400076, India; 
Planetary and Geosciences Division, Physical Research Laboratory (PRL), Navrangpura, Ahmedabad 380009, India; 
Department of Earth Sciences, Pondicherry University, Puducherry 605014, India
ABSTRACT: Barren Island (India) is a relatively little studied, little known active volcano in the Andaman Sea, and the northernmost active volcano of the great Indonesian arc. The volcano is built of prehistoric (possibly late Pleistocene) lava flows (dominantly basalt and basaltic andesite, with minor andesite) intercalated with volcaniclastic deposits (tuff breccias, and ash beds deposited by pyroclastic falls and surges), which are exposed along a roughly circular caldera wall. There are indications of a complete phreatomagmatic tephra ring around the exposed base of the volcano. A polygenetic cinder cone has existed at the centre of the caldera and produced basalt-basaltic andesite aa and blocky aa lava flows, as well as tephra, during historic eruptions (1787-1832) and three recent eruptions (1991, 1994-95, 2005-06). The recent aa flows include a toothpaste aa flow, with tilted and overturned crustal slabs carried atop an aa core, as well as locally developed tumuli-like elliptical uplifts having corrugated crusts. Based on various evidence we infer that it belongs to either the 1991 or the 1994-95 eruptions. The volcano has recently (2008) begun yet another eruption, so far only of tephra. We make significantly different interpretations of several features of the volcano than previous workers. This study of the volcanology and eruptive styles of the Barren Island volcano lays the ground for detailed geochemical-isotopic and petrogenetic work, and provides clues to what the volcano can be expected to do in the future. © Springer-Verlag 2009.
AUTHOR KEYWORDS: Andaman and Nicobar Islands;  Andaman Sea;  Barren Island;  India;  Indian Ocean;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Caruso, A.a , Censi, P.b , Aricò, P.b , Meli, C.b , Sprovieri, M.c 
Astronomical dating of two Pliocene alkaline volcanic ash layers in the Capo Rossello area (Southern Sicily, Italy): Implications for the beginning of the rifting in the Sicily channel
(2009) Bulletin de la Societe Geologique de France, 180 (2), pp. 95-104. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-65349150527&partnerID=40&md5=6a784fb245795da05eabd97e7d1c2bce
AFFILIATIONS: Dipartimento di Geologia e Geodesia, Université di Palermo, via Archirafi 22, 90123 Palermo, Italy; 
Dipartimento di Chimica e Fisica della Terra (CFTA), Universitè di Palermo, Via Archirafi 36, 90123 Palermo, Italy; 
IAMC Sezione Geomare Sud, CNR Calata Porta di Massa Interno porto di Napoli, 80100 - Napoli, Italy
ABSTRACT: Two volcaniclastic ash layers (AL1 and AL2) are intercalated throughout the middle Pliocene sedimentary sequences of Punta Piccola and Capo Rossello exposed along the south coast of Sicily (Italy). Astronomical calibration of the Punta Piccola section provided an age of 2.676 Ma for the deposition of the AL1 layer. The high-resolution bio-cyclostratigraphy of the Capo Rossello section, in combination with detailed correlations with previously astronomically calibrated coeval sequences, provided an age of 2.225 Ma for the deposition of the AL2 layer. Mineralogical, petrographical and geochemical results from the two volcaniclastic layers suggest a Na-alkaline differentiated magmatism for the volcanic source, similar to the one which formed the alkaline rocks of the island of Pantelleria (Sicily Channel). These results indicate that isolated volcanic activity and/or early differentiated magmatic events may have occurred in the area of the Sicily channel well before the well-known late Pleistocene volcanic activity.
AUTHOR KEYWORDS: Astronomical calibration;  Biostratigraphy;  Pliocene;  Sicily channel rift;  Volcanic ash layers
DOCUMENT TYPE: Article
SOURCE: Scopus

Van Kranendonk, M.J.a , Kröner, A.b , Hegner, E.c , Connelly, J.d 
Age, lithology and structural evolution of the c. 3.53 Ga Theespruit Formation in the Tjakastad area, southwestern Barberton Greenstone Belt, South Africa, with implications for Archaean tectonics
(2009) Chemical Geology, 261 (1-2), pp. 114-138. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-62349130694&partnerID=40&md5=84974ded9f09b15bef12eba95776a4e5
AFFILIATIONS: Geological Survey of Western Australia, 100 Plain St, East Perth, WA 6004, Australia; 
Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany; 
Department für Geo-und Umweltwissenschaften, Universität München, Theresienstrasse 41, D-80333 München, Germany; 
Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712-1101, United States
ABSTRACT: A field and petrographic re-assessment of rocks from the Theespruit Formation near Tjakastad, southwestern Barberton Greenstone Belt, is combined with new zircon U-Pb ages and whole-rock Sm-Nd isotopic results to reveal several important inconsistencies with a previous thrust-accretion model for this area. It was found that faults previously interpreted as 'thrusts' are extensional, 'thrust slices of basement orthogneiss' are little deformed quartz-feldspar porphyries or sheared felsic volcaniclastic sedimentary rocks, and 'sedimentary diamictites' are felsic agglomerates. These observations, combined with consistent facing directions of bedding, the recognition of distinct stratigraphic variations across strike, and U-Pb zircon dates from 13 felsic metavolcanic samples, all suggest that the Theespruit Formation is a moderately strained, coherent stratigraphic succession deposited at c. 3530 Ma and affected by extensional shear deformation at c. 3230 Ma. A 3453 ± 6 Ma population of zircons analysed previously from an amphibolite-facies Theespruit Formation felsic schist is interpreted as being of metamorphic, rather than detrital, origin, and arising from heat associated with felsic plutonic rocks that stitch the Theespruit Formation to the overlying Komati Formation at ca. 3450 Ma, 220 Ma earlier than the proposed thrusting event. Crown Copyright © 2008.
AUTHOR KEYWORDS: Archean;  Barberton greenstone belt;  Tectonics;  Theespruit Formation
DOCUMENT TYPE: Article
SOURCE: Scopus

Higaki, D.a , Yoshimura, N.b , Ohara, J.c 
Geomorphological and geological evolution processes and their relation to the underground water flow in Tanino-uchi Landslide, southwest Japan
(2009) Chikei/Transactions, Japanese Geomorphological Union, 30 (2), pp. 77-93. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649134783&partnerID=40&md5=52efa28e20b28e4707d976e6c48c1e64
AFFILIATIONS: Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8151, Japan; 
Shikoku Try, Co. Ltd., Kochi, 780-0082, Japan; 
Erosion and Sediment Control Research Group, Public Works Research Institute, Tsukuba, 305-8516, Japan
ABSTRACT: Geomorphic and geological evolution processes and their relation to the distribution of groundwater flow were investigated in the Tanino-uchi Landslide in southwest Japan. The landslide consists of the entire landslide block moving toward southeast and the lower landslide block moving eastward. The lower landslide block is divided into a, b, c, and d blocks. Three geological units originating from the accretionary complex were formed as the bed rock of the area, namely 1) mudstone dominant layers with a thin basalt volcaniclastic bed, 2) alternative layers of sandstone and mudstone, and 3) massive chert and basalt volcaniclastic rocks. A rockslide occurred along the slip surface in the thin basalt volcaniclastic bed within the present entire landslide block area about 19,000 years ago. In the incident, the sliding mass climbed towards southeast along the slip surface of north dipping which was formed at the toe of rockslide due to the southern wing of synclinal structure. As a result, terrace-like topography was also formed in a and b blocks. Subsequently the lower landslide block started to move eastward following the deposition pattern of clayey volcaniclastic rock taking a ship bottom feature in the south part of the entire landslide block. To identify the distribution of groundwater flow on the landslide slope, we investigated the rise and fall characteristics of groundwater levels after rainfall using boreholes, as well as the distribution of groundwater drainage effect by well construction. Consequently, two flow routes were found. One is the southeastward flow from the upper part of the entire landslide block. It travels above the impermeable volcaniclastic bed and caused gradual groundwater level changes. Another is the eastward flow from the head part of the lower landslide block causing the prompt groundwater level changes. The confluence of these flows and the terrace-like topography induce groundwater concentration at a and b blocks. As above, present groundwater flow is strongly controlled by geomorphic and geological formative processes. Therefore understanding of geomorphological and geological formative processes is important for effective countermeasure planning.
AUTHOR KEYWORDS: Geological structure;  Groundwater;  Landslide;  Microtopography;  Slope evolution
DOCUMENT TYPE: Article
SOURCE: Scopus

Christidis, G.E.a , Huff, W.D.b 
Geological aspects and genesis of bentonites
(2009) Elements, 5 (2), pp. 93-98. Cited 9 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649277709&partnerID=40&md5=604f98a78771ef86720419d1b2910399
AFFILIATIONS: Technical University of Crete, Department of Mineral Resources Engineering, 73100 Chania, Greece; 
Department of Geology, University of Cincinnati, Cincinnati, OH 45221, United States
ABSTRACT: Bentonites are clay rocks consisting predominantly of smectite. They form mainly from alteration of pyroclastk and/or volcaniclastic rocks. Extensive deposits, linked to large eruptions, have formed repeatedly in the past. Bentonite layers are useful for stratigraphie correlation and for interpreting the geodynamic evolution of our planet. Bentonites generally form by diagenetic or hydrothermal alteration, favoured by fluids that leach alkali elements and by high Mg content. Smectite composition is partly controlled by parent rock chemistry. Recent studies have shown that bentonite deposits may display cryptic variations in layer charge - i.e. the variations are not visible at the macroscopic scale - and these correlate with physical properties.
AUTHOR KEYWORDS: Bentonite;  Clay;  Cryptic variation;  Glass alteration;  Smectite;  Stratigraphie correlation
DOCUMENT TYPE: Article
SOURCE: Scopus

Mitchell, S.F., Ramsook, R.
Rudist bivalve assemblages from the Back Rio Grande Formation (Cretaceous: Campanian) of Jamaica and their stratigraphic significance
(2009) Cretaceous Research, 30 (2), pp. 307-321. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-62049083795&partnerID=40&md5=7c6ca1235d9827011fc4d26c8f0f7a2d
AFFILIATIONS: Department of Geography and Geology, University of the West Indies, Mona, Kingston 7, Jamaica
ABSTRACT: The lithostratigraphy of the Back Rio Grande Formation (Campanian) in the Blue Mountains of eastern Jamaica is described. Six informal members are recognised; three limestone and three volcaniclastic units. The rudist assemblages from the three limestone members are described, and the occurrence of larger foraminifers is discussed. The lower limestone member yields Barrettia monilifera Woodward, Durania krijneni sp. nov., Chiapasella cubensis Rutten, Bournonia thiadensi Vermunt, Branislavia stellaplicatus sp. nov. and Antillosarcolites? cf. macgillavryi Chubb together with several forms left in open nomenclature as well as the larger foraminifer Pseudorbitoides trechmanni Douvillé. The middle limestone member yields D. krijneni sp. nov. and C. cubensis. In the upper limestone member occur Barrettia sp. A, D. krijneni sp. nov., C. cubensis, Titanosarcolites sp. A and A.? cf. macgillavryi Chubb together with larger foraminifers including Pseudorbitoides and Vaughanina cubensis Palmer. The lower limestone member is placed in the middle Campanian, and the upper limestone member together with the overlying Rio Grande Formation are assigned a late Campanian age on the basis of their rudist and larger foraminifer assemblages. Chiapasella cubensis is recognised as a good marker for both the middle and upper Campanian. © 2008 Elsevier Ltd. All rights reserved.
AUTHOR KEYWORDS: Biostratigraphy;  Campanian;  Cretaceous;  Larger foraminifers;  Palaeontology;  Rudist bivalves
DOCUMENT TYPE: Article
SOURCE: Scopus

Luo, Y.a  b , Niu, H.C.a , Shan, Q.a , Zhang, B.c , Zhou, C.P.c , Yang, W.B.a  b , Yu, X.Y.a 
Discovery of the basaltic andesite-high-K basaltic andesite-trachyandesite association in the Yuximolegai Daban, West Tianshan and its geological significance
(2009) Acta Petrologica Sinica, 25 (4), pp. 934-943. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69649086408&partnerID=40&md5=2292f61cfc3e7533f677e26ae46e74dc
AFFILIATIONS: Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 
Graduate University, Chinese Academy of Sciences, Beijing 100049, China; 
No. 7 Geological Survey Team, Xinjiang Bureau of Geology and Mineral Resource Exploration, Wusu 833000, China
ABSTRACT: Within the Yuximolegai Daban of eastern Awulale, West Tianshan, the Dahalajunshan Formation is mainly composed of andesitic (trachyandesitic)- dacitic(trachytic-trachydacitic)lavas and volcaniclastic rocks. Based on the petro-geochemical features, an association of calc-alkaline basaltic andesite-high-K calc-alkaline basaltic andesite-trachyandesite (shoshonite series) has been recognized from the upper part of volcanic rocks in the Dahalajunshan Formatioa The trace element characteristics show that three kinds of volcanic rocks were formed in the island arc environment The generation of the calc-alkaline basaltic andesite was related to the slab subduction, while the high-K calc-alkaline basaltic andesite and trachyandesite were related to the asthenospheric upwelling induced by the subducted slab break off. The existence of this association implies that the tectonic system has been changed from compression to extension during Late Carboniferous due to the the subducted slab break off. This association is quite similar to those related to the Cu-Au mineralization in the world,for instance, that in Papua New Guinea, indicating that the Late Carboniferous has a better Cu-Au ore-forming prospect in this region.
AUTHOR KEYWORDS: Calc-alkaline basaltic andesite;  High-K calc-alkaline basaltic andesite;  Late Carboniferous;  Trachyandesite;  Yuximolegai Daban
DOCUMENT TYPE: Article
SOURCE: Scopus

Vera, E.A.R.a , Folguera, A.a , Gímenez, M.b , Martínez, P.b , Ruiz, F.b , Ramos, V.A.a 
Tectonic evolution of the Loncopué trough: Structure of the Quaternary Huecú depocenter and its relation to the sedimentation and volcanism [Evolución tectónica de la fosa de loncopué: Estructura del depocentro cuaternario del huecú y su relación con la sedimentación y el volcanismo]
(2009) Revista de la Asociacion Geologica Argentina, 64 (2), pp. 214-230. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349667222&partnerID=40&md5=0b1afd0052f2b537c51838f7b31f7706
AFFILIATIONS: Laboratorio de Tectónica Andina, FCEyN, Universidad de Buenos Aires - Conicet; 
Instituto Volponi, Universidad Nacional de San Juan-Conicet
ABSTRACT: The Huecú basin is located at the central part of the large Loncopué retroarc trough. Its volcanic, volcaniclastic, lacustrine and fluvial filling is directly related to neotectonic activity in the area. The basaltic eruptions are reflecting different pulses associated with the development of extensional faults and tensional fractures. Geophysical potential methods have identified basement involvement in the extensional deformation that affected the Tertiary sequences of the area during the last 5 Mys. Neotectonic features in Quaternary volcanic sequences suggest the persistence of these subsidence mechanisms in the Huecú depocenter. These faults are directly connected to the basement segmentation identified by gravimetric and mag-netometric studies. The historical floods produced by the Agrio river damming, are related to fisural eruptions and demons-trate the high probability that retroarc volcanic eruptions may occur again. The recognition of flooded areas that are forming the youngest sedimentary levels in the Huecú depocenter shows potential areas of active retroarc spreading in the Neuquén area associated with neotectonic and seismic processes.
AUTHOR KEYWORDS: Andes;  Damming;  Loncopué;  Neotectonics;  Volcanism
DOCUMENT TYPE: Article
SOURCE: Scopus

Nie, X.-Y.a  b  c , Song, X.-Y.a , Bo, K.-W.c , Zhang, W.-Z.c , Liu, T.c 
The Geological-geochemical Characteristics and Genesis of Shuangquan Typical Gold Deposit in Kalameily Belt, East Junggar, Xinjiang
(2009) Bulletin of Mineralogy Petrology and Geochemistry, 28 (2), pp. 169-176. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349308486&partnerID=40&md5=dcf6fdc699a9a94b3d0fb8e00112a993
AFFILIATIONS: Institute of Geochemistry of Chinese, Academy of Sciences, Guiyang 550002, China; 
Graduate School of Chinese, Academy of Sciences, Beijing 100049, China; 
No.8 Geological Party of CAPF, Urumchi 830057, China
ABSTRACT: Shuangquan gold deposit is a medium size tectono-alteration ore gold deposit recently discovered in kalameily gold metallogenic belt of east junggar. The deposit is hosted in ductile shear zone and occurs in Nanmingshui group formation of Lower Carboniferous. The Au ore types are mostly metamorphic rock. Based on EPMA analysis of arsenopyrite and the phase diagram of coexisting minerals pyrite-arsenopyrite, we conclud that temperature of the main mineralization stage is stable within 300~450°C. This temperature reflects the mineralization temperature much better than the homogenization temperature obtained from inclusion fluid. The isotopic compositions of oxygen and hydrogen calculated under such average temperature are more accurate when tracing the origin of ore-forming fluids. The narrow variation of hydrogen and oxygen isotope could be resulted from the stage changes of temperature and composition of ore-forming fluids. Application of geological and geochemical data show that Shuangquan gold deposit is a metamorphic hydrothermal gold deposit related to ductile shear zone. Ductile shear zones provid the ore-transmitting structure and ore-depositing structures. The sources of ore-forming material may be originated from volcanic rocks and volcaniclastic rocks in Nanmingshui group formation of Lower Carboniferous.
AUTHOR KEYWORDS: Coexisting minerals;  Kalameily gold metallogenic belt;  Mineralization stage;  Shuangquan gold deposit;  Temperature of mineralization
DOCUMENT TYPE: Article
SOURCE: Scopus

Escrig, S.a , Bézos, A.a , Goldstein, S.L.b  c , Langmuir, C.H.a , Michael, P.J.d 
Mantle source variations beneath the eastern lau spreading center and the nature of subduction components in the lau basin-tonga arc system
(2009) Geochemistry, Geophysics, Geosystems, 10 (4), art. no. Q04014, . Cited 8 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-72449211822&partnerID=40&md5=7b4196e8d3662b03d5e3a0e539ac420c
AFFILIATIONS: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States; 
Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, 61 Route 9W, Palisades, NY 10964, United States; 
Department of Earth and Environmental Sciences, Columbia University, 61 Route 9W, Palisades, NY 10964, United States; 
Department of Geosciences, University of Tulsa, 800 South Tucker Avenue, Tulsa, OK 74104, USA, United States
ABSTRACT: [1] New high-density sampling of the Eastern Lau Spreading Center provides constraints on the processes that affect the mantle wedge beneath a back-arc environment, including the effect of the subduction input on basalt petrogenesis and the change in subduction input with distance from the Tonga arc. We obtained trace element and Pb-Sr-Nd isotopic compositions of 64 samples distributed between 20.2°S and 22.3°S with an average spacing of ̃3.6 km. The trace element and isotope variations do not vary simply with distance from the arc and reflect variations in the mantle wedge composition and the presence of multiple components in the subduction input. The mantle wedge composition varies form north to south, owing to the southward migration of Indian-like mantle, progressively replacing the initially Pacific-like mantle wedge. The mantle wedge compositions also require an enriched mid-ocean ridge basalt-like trace element enrichment that has little effect on isotope ratios, suggesting recent low-degree melt enrichment events. The composition of the subduction input added to the mantle wedge is geographically variable and mirrors the changes observed in the Tonga arc island lavas. The combination of the back-arc and arc data allows identification of several components contributing to the subduction input. These are a fluid derived from the altered oceanic crust with a possible sedimentary contribution, a pelagic sediment partial melt, and, in the southern Lau basin, a volcaniclastic sediment partial melt. While on a regional scale, there is a rough decrease in subduction influence with the distance from the arc, on smaller scales, the distribution of the subduction input reflects different mechanisms of the addition of the subduction input to a variable mantle wedge. © 2009 by the American Geophysical Union.
AUTHOR KEYWORDS: Back-arc basalt;  Back-arc basin;  Enrichment processes;  Mantle wedge;  Subduction component
DOCUMENT TYPE: Article
SOURCE: Scopus

Brown, D.J.a , Holohan, E.P.b , Bell, B.R.a 
Sedimentary and volcano-tectonic processes in the British Paleocene Igneous Province: A review
(2009) Geological Magazine, 146 (3), pp. 326-352. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70349378601&partnerID=40&md5=82a6dbb9338de28b0abd8835467fb170
AFFILIATIONS: Department of Geographical and Earth Sciences, University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom; 
School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland
ABSTRACT: Research on the British Paleocene Igneous Province (BPIP) has historically focused on the emplacement, chemistry and chronology of its elaborate central intrusive complexes and lava fields. However, the BPIP has also been dramatically shaped by numerous erosion, sedimentation and volcano-tectonic events, the significance of which becomes ever clearer as localities in the BPIP are re-investigated and our understanding of volcano-sedimentary processes advances. The resultant deposits provide important palaeo-environmental, palaeo-geographical and stratigraphical information, and highlight the wide range of processes and events that occur in ancient volcanic settings such as the BPIP. In this paper we review the sedimentary and volcano-tectonic processes that can be distinguished in the BPIP, and conceptualize them within a generalized framework model. We identify, and describe, the sedimentary responses to four broadly chronological stages in the history of the BPIP volcanoes: (1) the development of the lava fields, (2) early intrusion-induced uplift, (3) caldera collapse and (4) post-volcano denudation and exhumation of central complexes. We highlight and illustrate the range of sedimentary processes that were active in the BPIP. These operated on and helped shape a dynamic landscape of uplands and lowlands, of alluvial fans, braided rivers, lakes and swamps, and of volcanoes torn apart by catastrophic mass wasting events and/or caldera collapse. © 2009 Copyright © Cambridge University Press 2009.
AUTHOR KEYWORDS: British Paleocene Igneous Province;  Caldera;  Debris flow;  Fluvio-lacustrine;  Mass wasting;  Sedimentary;  Volcaniclastic;  Volcano-tectonics
DOCUMENT TYPE: Review
SOURCE: Scopus

Gernon, T.M.a , Field, M.a  b , Sparks, R.S.J.a 
Depositional processes in a kimberlite crater: The Upper Cretaceous Orapa South Pipe (Botswana)
(2009) Sedimentology, 56 (3), pp. 623-643. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-62549149910&partnerID=40&md5=c19e5e26f3903bdf74ee76bb12cc62f3
AFFILIATIONS: Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom; 
De Beers MRM R and D Group, Mendip Court, Bath Road, Wells BA5 3DG, United Kingdom
ABSTRACT: The Orapa A/K1 Diamond Mine, Botswana, exposes the crater facies of a bilobate kimberlite pipe of Upper Cretaceous age. The South Crater consists of layered volcaniclastic deposits which unconformably cross-cut massive volcaniclastic kimberlite of diatreme facies in the North Pipe. Based on the depositional structure, grain-size, sorting and composition of kimberlite in the South Crater, six units are distinguished in the ∼70m thick stratiform crater-fill sequence and talus slope deposits close to the crater wall, which represents a multistage infill of the volcanic crater. Monolithic basalt breccias (Unit 1) near the base of the crater-fill are interpreted as rock-fall avalanche deposits, generated by the sector collapse of the crater walls. These deposits are overlain by a basal imbricated lithic breccia and upper massive sub-unit (Unit 2), interpreted as the deposits of a pyroclastic flow that entered the South Crater from another source. Vertical degassing structures within the massive sub-unit show evidence for elutriation of fines and probably were formed after emplacement by fluidization due to air entrainment. Units 3 and 5 are thinly stratified deposits, characterized by diffuse bedding, reverse and normal grading, coarse lenticular beds, mudstone beds, small-scale scour channels and load casts. These units are attributed to rapidly emplaced sheet floods on the crater floor. Units 3 and 5 are directly overlain by poorly sorted volcaniclastic kimberlite (Units 4 and 6) rich in basalt boulders, attributed to debris flows formed by the collapse of crater walls. Unit 7 comprises medium sandstones to cobble conglomerates representing talus fans, which were active throughout the deposition of Units 1 to 6. The study demonstrates that much of the material infilling the South Crater is derived externally after eruption, including primary pyroclastic flow deposits probably from another kimberlite pipe. These findings have important implications for predicting diamond grade. Results may also aid the interpretation of crater sequences of ultra-basic, basaltic and intermediate volcanoes, together with the deposits of topographic basins in sub-aerial settings. © 2008 The Authors. Journal compilation © 2008 International Association of Sedimentologists.
AUTHOR KEYWORDS: Crater infill;  Kimberlite;  Orapa;  Pyroclastic flow;  Sheet flood
DOCUMENT TYPE: Article
SOURCE: Scopus

del Potro, R.a  b , Pinkerton, H.a , Hürlimann, M.c 
An analysis of the morphological, geological and structural features of Teide stratovolcano, Tenerife
(2009) Journal of Volcanology and Geothermal Research, 181 (1-2), pp. 89-105. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-60749122542&partnerID=40&md5=adb6c30f771de3e9906ae855ac53f226
AFFILIATIONS: Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, United Kingdom; 
Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apdo. 86-3000, Heredia, Costa Rica; 
Geotechnical Engineering and Geosciences Department, Technical University of Catalonia (UPC), Jordi Girona 1-3 (D2), 08034 Barcelona, Spain
ABSTRACT: A combined field, GIS and modelling study has given us new insights into the evolution and morphology of Teide stratovolcano in the central part of Tenerife. Central to our analysis was an investigation of the nature and development of a number of enigmatic morphological features, including two large 'bulges' at mid-elevation in the north-western and east-north-eastern flanks. This entailed a detailed analysis of high resolution digital elevation data, coupled with new photogeological, geological and geomorphological surveys which were examined using GIS. Our geological investigations reveal that widespread deposits on the steep northern flanks of the edifice were volcaniclastic deposits. These formed during the collapse of incandescent lava flow fronts and, possibly, domes and lobes. Careful examination of other deposits on the lower north-western flank has shown that they formed during magma-water interactions. Detailed analysis has revealed the presence of small coulée eruption vents, abrupt terminations to lava flows and vertical scarps. We were also able to confirm the presence of two nested gräben, along which there has been extensive hydrothermal alteration. Finite element modelling of the basement beneath Teide and structural stability suggest that the Teide edifice was emplaced on the headwall of the Icod island flank collapse. We conclude that the two bulges are flank vents, similar to Pico Viejo, although on a smaller scale. The presence of these flank vents suggests that conduit blockage has probably been more common than previously estimated on Teide. We suggest that future hazard mitigation measures should take into account the potential for large flank vents forming during future eruptions, the possibility of explosive activity from the central edifice, and pyroclastic density currents in front of advancing flows on the flanks of Teide. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Teide;  Tenerife;  volcanic evolution;  volcaniclastic deposits
DOCUMENT TYPE: Article
SOURCE: Scopus

Mueller, W.U.a , Stix, J.b , Corcoran, P.L.c , Daigneault, R.a 
Subaqueous calderas in the Archean Abitibi greenstone belt: An overview and new ideas
(2009) Ore Geology Reviews, 35 (1), pp. 4-46. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-60949097624&partnerID=40&md5=d63174f02264373496bf419ae4ec1252
AFFILIATIONS: Sciences de la terre, Université du Québec à Chicoutimi, Canada; 
Department of Earth and Planetary Sciences, McGill University, Canada; 
Department of Earth Sciences, University of Western Ontario, Canada
ABSTRACT: The 300 × 700 km Abitibi greenstone belt in Canada contains numerous world class Archean volcanogenic massive sulfide (VMS) deposits, yet documentation of Archean subaqueous calderas hosting such deposits is lacking. The modern Sunrise deposit in the Myojin Knoll caldera of the Izu-Bonin arc shows that submarine calderas are first order sites for VMS. The Hunter Mine and Normetal calderas, as well as the Blake River megacaldera complex are reviewed with respect to geometry, regional geology, physical volcanology, dyke emplacement, and hydrothermal carbonate alteration. These subaqueous calderas are placed into the geodynamic context of the Abitibi greenstone belt. The Abitibi belt displays a complex history of oceanic arc formation, evolution, collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes. Analogue models yielding new insights into the sequence of caldera-forming events and their synvolcanic fault patterns are applied to explain Archean examples. Underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events. During subsidence, two sets of faults propagate from the magma chamber margin: (1) early reverse (outward dipping) faults, and (2) normal (inward dipping) faults. The largest massive sulfide deposits form preferentially at the caldera margin. Based on experimental studies and detailed facies mapping, the Hunter Mine caldera is of the segmented, piecemeal variety, and the Normetal caldera is akin to a piston structure. The Blake River megacaldera contains (1) the E-W trending Misema, (2) the NW-trending New Senator, and (3) the NE-trending Noranda calderas with the latter two being nested graben-type calderas, consistent with oblique Archean subduction. The poorly-documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented. The alteration study was evaluated at three levels: microprobe analysis, geochemical staining of drill core, and whole rock analyses. There were two principal stages of alteration related to VMS formation. An early silicification phase developed either at depth and/or at the seawater interface, whereby silicification was bedding parallel in fine-grained volcaniclastic deposits near the water surface. A pervasive and extensive semi-conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently. Three distinct carbonate pairings were observed: (1) proximal siderite (sideroplesite) - Fe-ankerite next to the VMS-deposit, (2) an intermediate ankerite-Fe-dolomite zone and (3) a distal calcite-dolomite zone. The carbonate phase is associated with the mineralizing event. Transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap. The silica-carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented. This alteration can be easily confused with primary carbonates and chemical precipitation deposits (e.g. banded iron-formation) if detailed volcano-sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Abitibi belt;  Archean calderas;  Carbonate alteration;  Exploration model;  VMS deposits;  Volcanology
DOCUMENT TYPE: Article
SOURCE: Scopus

Vishnevskaya, V.S.a , Djeric, N.b , Zakariadze, G.S.c 
New data on Mesozoic Radiolaria of Serbia and Bosnia, and implications for the age and evolution of oceanic volcanic rocks in the Central and Northern Balkans
(2009) Lithos, 108 (1-4), pp. 72-105. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-59949090244&partnerID=40&md5=7fc3fa2a7f5c12a5526803cc020d8b66
AFFILIATIONS: Geological Institute, Russian Academy of Sciences, 119017 Moscow, Russian Federation; 
Faculty of Mining and Geology, Beograd University, Beograd, Serbia; 
Vernadsky Institute Russian Academy of Sciences, 119991 Moscow, Russian Federation
ABSTRACT: The Dinaridic Ophiolite Belt (DOB) includes Middle Triassic cherty limestones, Upper Triassic radiolarian cherts associated with basaltic lavas and volcaniclastic sediments, and also Jurassic continental slope sequences. Sedimentary sequences grade upwards into Cretaceous red limestones with planktonic foraminifers of the Genus Hedbergella. Many of the Late Triassic to Late Jurassic cherts probably accumulated in an oceanic setting, and now crop out as blocks in olistostromal deposits. Jurassic radiolarite sequences of the margin of the Dinaride Ophiolite Belt are represented by Aalenian, Upper Bajocian-Lower Bathonian and Upper Bathonian-Lower Callovian, Middle Callovian-Oxfordian, Upper Callovian-Upper Oxfordian and Kimmeridgian-Tithonian-aged strata. These are overlain by Upper Tithonian-Valanginian sedimentary sequences with spongolite-radiolarites, volcaniclastic sediments and other continental slope deposits. The oldest units outcropping in the DOB are Mid-Triassic (Ladinian) red cherts and limestones. These are associated with alkaline and tholeiitic basalts in the Bistrica area, and with tholeiitic basalts in the Visoka area. In contrast, in the Vardar Zone Western Belt the oldest basalt-radiolarite formation is represented by cherts associated with tholeiitic basalt in the Ovčar Banja area. Upper Triassic red radiolarites of the Čačak area lie in direct stratigraphical contact with MORB-type pillow lavas and contain a Carnian-Norian radiolarian assemblage. The youngest radiolarian-bearing units are in the Upper Cretaceous part of the Vardar Zone Western Belt, in the Struganik area, where Coniacian-Santonian radiolarians occur in chert-clay-tuff sediments. In addition, cherty limestones from the northern slope of Kozara Mt. contain a Campanian radiolarian assemblage, together with Campanian-Maastrichtian planktonic foraminifers. Volcanic units associated with the siliceous sediments of Dinaride Ophiolite Belt and the Vardar Zone Western Belt are of MOR- and SSZ types, respectively. The ocean-related basalts of the Dinaride Ophiolite Belt and the Vardar Zone Western Belt show some geochemical differences, irrespective of age. Compared to those of the Dinaride Ophiolite Belt, the basalts of the Vardar Zone Western Belt are more variable chemically and exhibit much higher LREE/HREE and Th/REE ratios. Finally, possible paleo-reconstructions of the radiolarian sediments and the volcanic rocks are proposed. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Bosnia;  Mesozoic;  Palaeogeography;  Radiolaria;  Serbia
DOCUMENT TYPE: Article
SOURCE: Scopus

Shin, D.a , Lee, J.-I.b , Hwang, J.c , Hur, S.-D.b 
Hydrothermal alteration and isotopic variations of igneous rocks in Barton Peninsula, King George Island, Antarctica
(2009) Geosciences Journal, 13 (1), pp. 103-112. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-64249150667&partnerID=40&md5=88fb514d56240ddb36f82c1a09117d15
AFFILIATIONS: Department of Geoenvironmental Sciences, Kongju National University, Kongju 314-701, South Korea; 
Korea Polar Research Institute, P.O. Box 32, Incheon 406-600, South Korea; 
Department of Geological Engineering, Daejeon University, Daejeon 300-716, South Korea
ABSTRACT: O, H, S and Sr isotopes were investigated to characterize the nature of hydrothermal fluids and alteration processes in volcanic and intrusive rocks in Barton Peninsula, King George Island. The oxygen and hydrogen isotope compositions of altered basaltic andesite and granodiorite are similar to each other. The δ18O and δD values gradually decrease from altered basaltic andesite to altered dyke and quartz-veined volcaniclastic rock. The genetic linkage between hydrothermal fluid and granodiorite intrusion accounts for similar δ34S values among sulfide minerals, both in the granodiorite stock and in nearby altered basaltic andesite. Broadly positive correlations of δ18O-SiO2, δ18O-(87Sr/86Sr)i, and 87Sr/86Sr-SiO2 can be established by siliceous fluids enriched in 18O as well as 87Sr. In addition, a positive relationship between (87Sr/86Sr)i values and 1/Sr contents in basaltic andesites can result from mixing between fresh rocks and infiltrating fluids with different endmember 87Sr/86Sr values and Sr contents. The hyperbolic variation of (87Sr/86Sr)i-K/Rb suggests that meteoric water participated in hydrothermal activities via mixing with magmatic water, and the contribution of seawater was insignificant. All of the above results indicate that hydrothermal alteration was influenced by fluids related to granodiorite intrusion, and 18O- and 87Sr-rich meteoric water circulating in the upper crust significantly contributed to hydrothermal activities in Barton Peninsula. © 2009 The Association of Korean Geoscience Societies.
AUTHOR KEYWORDS: Antarctica;  Barton Peninsula;  Hydrothermal alteration;  Isotope;  Volcanic rock
DOCUMENT TYPE: Article
SOURCE: Scopus

Windley, B.F.a , Garde, A.A.b 
Arc-generated blocks with crustal sections in the North Atlantic craton of West Greenland: Crustal growth in the Archean with modern analogues
(2009) Earth-Science Reviews, 93 (1-2), pp. 1-30. Cited 14 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-60549092845&partnerID=40&md5=29d29b2f582ccd70bd278aa7e22c0bcb
AFFILIATIONS: Department of Geology, The University of Leicester, Leicester, LE1 7RH, United Kingdom; 
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
ABSTRACT: The ca. 700 km long, Archean craton of West Greenland consists of six Meso-Neoarchean (ca. 3000-2720 begin_of_the_skype_highlighting              3000-2720      end_of_the_skype_highlighting Ma) shear zone - bounded crustal blocks that display similar cross-sections; from south to north Ivittuut, Kvanefjord, Bjørnesund, Sermilik, Fiskefjord, Maniitsoq. Each block has a southerly upper and a northerly lower zone, thus each faces upwards to the south. Upper zones have prograde amphibolite facies mineralogy and have never been in the granulite facies, whereas lower zones reached granulite facies and were partly retrogressed to amphibolite facies. Upper and lower zones consist predominantly of tonalite-trondhjemite-granodiorite (TTG) orthogneisses; geochemistry suggests generation by slab melting in subduction settings of island arcs and active continental margins. The gneisses contain km-thick metavolcanic amphibolite layers typically bordered by km-thick layers containing anorthosite and leucogabbro. Most upper zones contain upper greenschist to amphibolite facies metavolcanic belts including volcaniclastic, andesitic rocks. The two most-prominent metavolcanic belts in the Fiskefjord block at Qussuk (andesitic-volcaniclastic rocks; Garde, A.A., 2007. A mid-Archaean island arc complex in the eastern Akia terrane, Godthåbsfjord, southern West Greenland. Journal of the Geological Society (London) 164, 565-579.) and Ivisaartoq (mafic-ultramafic rocks and anorthosite-leucogabbro from upper and lower parts of a supra-subduction zone system; Polat, A., Frei, R., Appel, P.W.U., Dilek, Y., Fryer, B., Ordóñez-Calderón, J.C., Yang, Z., 2008. The origin and compositions of Mesoarchean oceanic crust: evidence from the 3075 Ma Ivisaartoq greenstone belt, SW Greenland. Lithos 100, 293-321.) have island arc geochemical signatures. The 2 km-thick Fiskenæsset complex (Bjørnesund block) comprises chromite-layered anorthosites, leucogabbros and gabbros, and local pillow-bearing roof pendants from overlying metavolcanic amphibolite. The style of deformation changes downwards within crustal blocks; upper zones are characterised by linear metavolcanic belts deformed by mostly one major phase of isoclinal folding, and lower zones by kilometre-scale double-triple fold interference patterns. Everywhere TTG protoliths have intruded anorthositic and volcanic rocks typically along ductile shear zones, often so extensively that only anorthositic or amphibolitic lenses are preserved. The Meso-Neoarchean crust was thickened by a combination of thrusting, isoclinal folding and continued TTG injection. Dissimilarities in the proportions of anorthositic and metavolcanic rocks in the six blocks suggest that they evolved in several different microcontinents but by similar processes. These crustal blocks provide an exceptional example of how continents evolved in the Meso-Neoarchean. Comparable Archean examples in Kapuskasing and Pikwitonei (Canada) and modern analogues in Fiordland (New Zealand), Kohistan (Himalayas), Southern California batholith, Peruvian Andes, and Hidaka (Japan) demonstrate that processes of continental growth from island arc to continental arc magmatism (and by implication to continental collision) were broadly similar throughout most of Earth history. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: anorthosite;  Archean;  crustal block;  island arc;  metavolcanic amphibolite;  TTG;  West Greenland
DOCUMENT TYPE: Review
SOURCE: Scopus

Bouabdellah, M.a , Beaudoin, G.b , Leach, D.L.c , Grandia, F.d , Cardellach, E.d 
Genesis of the Assif El Mal Zn-Pb (Cu, Ag) vein deposit. An extension-related Mesozoic vein system in the High Atlas of Morocco. Structural, mineralogical, and geochemical evidence
(2009) Mineralium Deposita, 44 (6), pp. 689-704. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68249138440&partnerID=40&md5=36ac3c34df1a987a625b14be2d85eb1d
AFFILIATIONS: Faculté des Sciences, Laboratoire des Gétes Minéraux, Hydrogéologie and Environnement, Oujda 60000, Morocco; 
Département de Géologie et de Génie Géologique, Université Laval, Québec, QC G1K 7P4, Canada; 
US Geological Survey, Box 25046 MS973, Denver, CO 80225, United States; 
Departament de Geologia, Universitat Autónoma de Barcelona, Edifici C, 08193 Bellaterra, Barcelona, Spain
ABSTRACT: The Assif El Mal Zn-Pb (Cu-Ag) vein system, located in the northern flank of the High Atlas of Marrakech (Morocco), is hosted in a Cambro-Ordovician volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered with minor tuff and mudstone. Intrusion of synorogenic to postorogenic Late Hercynian peraluminous granitoids has contact metamorphosed the host rocks giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, amphibole, chloritoid, and garnet. The Assif El Mal Zn-Pb (Cu-Ag) mineralization forms subvertical veins with ribbon, fault breccia, cockade, comb, and crack and seal textures. Two-phase liquid-vapor fluid inclusions that were trapped during several stages occur in quartz and sphalerite. Primary inclusion fluids exhibit Th mean values ranging from 104°C to 198°C. Final ice-melting temperatures range from -8.1°C to -12.8°C, corresponding to salinities of ∼15 wt.% NaCl equiv. Halogen data suggest that the salinity of the ore fluids was largely due to evaporation of seawater. Late secondary fluid inclusions have either Ca-rich, saline (26 wt.% NaCl equiv.), or very dilute (3.5 wt.% NaCl equiv.) compositions and homogenization temperatures ranging from 75°C to 150°C. The δ18O and δD fluid values suggest an isotopically heterogeneous fluid source involving mixing between connate seawater and black-shale-derived organic waters. Low δ13CVPDB values ranging from -7.5‰ to -7.7‰ indicate a homogeneous carbon source, possibly organic matter disseminated in black shale hosting the Zn-Pb (Cu-Ag) veins. The calculated δ34SH2S values for reduced sulfur (22.5‰ to 24.3‰) are most likely from reduction of SO42- in trapped seawater sulfate or evaporite in the host rocks. Reduction of sulfate probably occurred through thermochemical sulfate reduction in which organic matter was oxidized to produce CO2 which ultimately led to precipitation of saddle dolomite with isotopically light carbon. Lead isotope compositions are consistent with fluid-rock interaction that leached metals from the immediate Cambro-Ordovician volcaniclastic and metasedimentary sequence or from the underlying Paleo-Neoproterozoic crustal basement. Geological constraints suggest that the vein system of Assif El Mal formed during the Jurassic opening of the central Atlantic Ocean. © Springer-Verlag 2009.
AUTHOR KEYWORDS: Assif El Mal;  Fluid inclusions;  Morocco;  Stable isotopes;  Zn-Pb vein deposits
DOCUMENT TYPE: Article
SOURCE: Scopus

Maldonado, F.a , Kelley, S.A.b 
Revisions to the stratigraphic nomenclature of the Abiquiu formation, abiquiu and contiguous areas, north-central New Mexico
(2009) New Mexico Geology, 31 (1), pp. 3-8. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-62649157945&partnerID=40&md5=cc8630d108119767eb36da4774bbacc9
AFFILIATIONS: U.S. Geological Survey, Denver Federal Center, Box 25046, Denver, CO 80225, United States; 
New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
ABSTRACT: Stratigraphic studies and geologic mapping on the Abiquiu 7.5-min quadrangle have led to revision of the stratigraphic nomenclature for the Oligocene to Miocene Abiquiu Formation in north-central New Mexico. The Abiquiu Formation had previously been defined to include informal upper, middle (Pedernal chert member), and lower members. The basement-derived conglomeratic lower member in the northern Jemez Mountains and Abiquiu embayment is here redefined. We propose removing the "lower member" from the Abiquiu Formation because provenance of these coarse sediments is dramatically different than the volcaniclastic strata of the "upper member." Furthermore, we propose that the term "lower member of the Abiquiu Formation" be replaced with an existing unit name, the Ritito Conglomerate of Barker (1958), and that the name Abiquiu Formation be restricted to the volcaniclastic succession. The lower part of the Ritito Conglomerate in Arroyo del Cobre on the Abiquiu quadrangle is 47 m (155 ft) thick and is composed of arkosic conglomeratic beds interbedded with arkosic sands and siltstones. Clasts include, in descending order of abundance, Proterozoic quartzite, granite, metavolcanic rocks, quartz, schist, and gneiss and a trace of Mesozoic sandstone and Paleozoic chert. Clasts are predominantly of pebble and cobble size but range from granule to boulder size. Paleocurrent data collected in the Arroyo del Cobre area indicate that the Ritito Conglomerate was deposited by a south-flowing river system during the Oligocene, eroding Laramide highlands such as the Tusas Mountains to the northeast, which contain predominantly Proterozoic rocks. This depositional setting has also been suggested by previous workers. The middle member or Pedernal chert member is present both at the top of the Ritito Conglomerate and as lenses within the lower part of the Abiquiu Formation. This post-depositional diagenetic chert remains an informal unit called the Pedernal chert.
DOCUMENT TYPE: Article
SOURCE: Scopus

Compton, P.M.
The geology of the Barmer Basin, Rajasthan, India, and the origins of its major oil reservoir, the Fatehgarh Formation
(2009) Petroleum Geoscience, 15 (2), pp. 117-130. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-70049088475&partnerID=40&md5=a6baf4f6fb23b48f320bb5ddcb886dc0
AFFILIATIONS: Cairn India Limited, Vipul Plaza, Sun City, Gurgaon 122002, Haryana, India
ABSTRACT: With the Mangala oil discovery in 2004, Cairn established the Barmer Basin of Rajasthan as a major new hydrocarbon province. Most reserves are contained in fluvial sandstone reservoirs of the Fatehgarh Formation, which probably ranges in age from Late Cretaceous to Early Paleocene. The Fatehgarh sandstones were mainly derived from reworking of Mesozoic sandstones at the northern end of the Barmer rift, but with some volcaniclastic input probably derived from Deccan volcanic rocks within and on the margins of the rift. These thick, quartz-rich, high porosity and permeability sandstones provide an excellent oil reservoir in the north of the Barmer Basin, but the increasing volcanic influence further south causes reservoir quality and thickness of net sand to deteriorate. This paper relates how the tectonic and volcanic evolution of the northwest margin of the Indian plate has influenced the depositional trends which have resulted in formation of this world class reservoir. © 2009 EAGE/Geological Society of London.
AUTHOR KEYWORDS: Barmer Basin;  Deccan Traps;  Fluvial sandstone reservoirs;  India;  Rift basin
DOCUMENT TYPE: Article
SOURCE: Scopus

Garzanti, E., Andò, S., Vezzoli, G.
Grain-size dependence of sediment composition and environmental bias in provenance studies
(2009) Earth and Planetary Science Letters, 277 (3-4), pp. 422-432. Cited 16 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-58149289701&partnerID=40&md5=f3878d94d52e0626d96306cdfb22cc24
AFFILIATIONS: Laboratorio di Petrografia del Sedimentario, Dipartimento di Scienze Geologiche e Geotecnologie, Università di Milano-Bicocca, 20126 Milano, Italy
ABSTRACT: This article investigates both experimentally and theoretically the compositional changes associated with textural effects and hydraulic sorting during sediment transport and deposition, which cause systematic distortion in quantitative provenance analysis ("environmental bias"). Traditional procedures aimed at eliminating textural noise find limited success. The Gazzi-Dickinson method cannot remove hydrodynamic-related modal variability. Multiple size-window strategies are time-consuming. Narrow or moving size-window strategies represent misleading or impractical short cuts, being less convenient options than simply analysing each sample in bulk. New concepts introduced here unravel the superposed causes of compositional variability in modern sediments. Intrasample modal variability, fundamentally explained by settling-equivalence relationships, can be accurately modelled mathematically. Intersample modal variability, principally resulting from selective entrainment, can be assessed and removed by a simple principle. In absence of provenance changes and environmental bias, the weighted average density of terrigenous grains (SRD index) should be equal, for each sample and each grain-size class of each sample, to the weighted average density of source rocks. By correcting relative abundances of detrital minerals in proportion to their densities, we can restore the appropriate SRD index for any provenance and subprovenance type in each sample or grain-size class. Modal variability is effectively reduced by this procedure, which can be applied confidently to modern sediments deposited by tractive currents in any environment. Good results are obtained even for placer sands and finest classes where heavy-mineral concentration is strongest. Such "SRD correction" also successfully compensates for biased narrow-window modes, thus providing a numerical solution of general validity to the problem of environmental bias in sedimentary petrology. After compensating for settling-equivalence and selective-entrainment effects, residual size-dependent compositional variability may be provenance-related. Minor in Ganga-Brahmaputra sediments, provenance-related effects are spectacularly displayed in the Nile basin, where volcaniclastic silt mixes with basement-derived quartzofeldspathic sand and wind-blown Saharan quartz. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: grain density;  heavy minerals;  hydraulic equivalence;  placer sands;  sedimentary petrology;  selective entrainment;  size-density sorting
DOCUMENT TYPE: Article
SOURCE: Scopus

Duuring, P.a  c , Rowins, S.M.a , McKinley, B.S.M.a , Dickinson, J.M.a , Diakow, L.J.b , Kim, Y.-S.c , Creaser, R.A.d 
Magmatic and structural controls on porphyry-style Cu-Au-Mo mineralization at Kemess South, Toodoggone District of British Columbia, Canada
(2009) Mineralium Deposita, pp. 1-28. Article in Press. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-58349093543&partnerID=40&md5=09ecbf0622751d1596ee83cf23fcf724
AFFILIATIONS: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, V6T 1Z4, Canada; 
British Columbia Geological Survey, Ministry of Energy, Mines and Petroleum Resources, Victoria, V8V 1X4, Canada; 
Department of Environmental Geosciences, Pukyong National University, Busan, 608-737, South Korea; 
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, T6G 2E3, Canada
ABSTRACT: Kemess South is the only Cu-Au-Mo mine in the Toodoggone district and a major Cu and Au producer in British Columbia. Porphyry-style Cu-Au-Mo mineralization is mainly hosted by the tabular, SW-plunging, 199.6 ± 0.6-Ma Maple Leaf granodiorite, which intrudes tightly folded, SW-dipping, Permian Asitka Group siltstone and limestone and homogeneous Triassic Takla Group basalt. Southwest-dipping 194.0 ± 0.4-Ma Toodoggone Formation conglomerate, volcaniclastic, and epiclastic rocks overlie the granodiorite and Asitka Group rocks. Minor Cu-Au-Mo mineralization is hosted by the immediate Takla Group basalt country rock, whereas low-tonnage high-grade Cu zones occur beneath a 30-m-thick leached capping in supergene-altered granodiorite and in exotic positions in overlying Toodoggone Formation conglomerate. Granodiorite has an intrusive contact with mineralized and altered Takla Group basalt but displays a sheared contact with unmineralized and less altered Asitka Group siltstone. The North Block fault is a deposit-scale, E-striking, steeply S-dipping normal fault that juxtaposes the granodiorite/basalt ore body against unmineralized Asitka Group rocks. Younger NW- and NE-striking normal-dextral faults cut all rock types, orebodies, and the North Block fault with displacements of up to 100 m and result in the graben-and-horst-style block faulting of the stratigraphy and ore body. Both basalt and granodiorite host comparable vein sequence and alteration histories, with minor variations in hydrothermal mineral assemblages caused by differing protolith chemistry. Early potassic alteration (and associated early-stage Cu ± Au ± Mo mineralization) is partly replaced by phyllic and intermediate argillic alteration associated with main-stage Cu-Au-Mo mineralization. Two main-stage veins have Re-Os molybdenite ages of 201.3 ± 1.2 and 201.1 ± 1.2 Ma. These mineralization ages overlap the 199.6 ± 0.6-Ma U-Pb zircon crystallization age for the Maple Leaf granodiorite. Late-stage pyrite-rich stringer veins and related phyllic alteration assemblages are cut by anhydrite-rich, carbonate-rich, and chlorite veins. Fluids and metals associated with early-, main-, and late-stage veins were probably derived principally from the same deep magma chamber as the Maple Leaf granodiorite. These magmatic-derived fluids interacted with Asitka and Takla Group country rocks and possibly with meteoric and metamorphic fluids prior to mineralization. © 2009 Springer-Verlag.
AUTHOR KEYWORDS: copper;  gold;  Kemess South;  Porphyry;  Stikine;  Toodoggone
DOCUMENT TYPE: Article in Press
SOURCE: Scopus

Cassidy, J.a , Ingham, M.b , Locke, C.A.a , Bibby, H.c 
Subsurface structure across the axis of the Tongariro Volcanic Centre, New Zealand
(2009) Journal of Volcanology and Geothermal Research, 179 (3-4), pp. 233-240. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-58249104261&partnerID=40&md5=2733283e3b0a09945b84bc2c3c1bf4a4
AFFILIATIONS: School of Geography, Geology and Environmental Science, The University of Auckland, Private Bag 92019, Auckland, New Zealand; 
School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand; 
GNS Science, Lower Hutt, New Zealand
ABSTRACT: The relationship between structure and volcanism in the Tongariro Volcanic Centre, New Zealand, is largely masked by a mantle of young volcanic deposits. Here we report the results of an integrated geophysical investigation (using gravity, multi-level aeromagnetic and magnetotelluric methods) of subsurface deposits and structures in the upper 1-2 km across the axis of the Tongariro Volcanic Centre. Modelling of these data across the Tama Lakes saddle shows that the outcropping volcanic deposits are up to 800 m thick, underlain by Tertiary sediments (of a few 10's to a few 100 m in thickness) and in turn lying above a basement of probable Mesozoic greywacke. Basement faulting is shown to be concentrated in the centre of the rift, which is 18 km wide at this location, but no vertical offset is resolved at the rift axis. Vertical displacements on basement faults of 250-300 m are modelled giving a minimum total basement subsidence of 650 m. A 5 km-wide, deep low resistivity zone occurs at the axis of the rift which is interpreted as either resulting from extensive fracturing and/or hydrothermal alteration within the basement. Steep-sided volcanic bodies with a high proportion of lavas/dykes coincide with the Waihi fault and the rift axis. Coincidence with the Waihi Fault suggests that this fault system may have provided magma pathways to the surface and a focus for dyke emplacement, which could have contributed to rift extension. The lack of offset at the rift axis may reflect the juvenile nature of faulting at this location, which is consistent with the notion of a migration of faulting towards the centre of the graben, alternatively, rifting may have been entirely accommodated by dyke emplacement. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: aeromagnetic;  gravity;  magnetotelluric;  rift structure;  Tongariro Volcanic Centre
DOCUMENT TYPE: Article
SOURCE: Scopus

Marren, P.M.a , Russell, A.J.b , Rushmer, E.L.c 
Sedimentology of a sandur formed by multiple jökulhlaups, Kverkfjöll, Iceland
(2009) Sedimentary Geology, 213 (3-4), pp. 77-88. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-60849105944&partnerID=40&md5=194d58c61b111fe9b3cd7880c5b6a3a7
AFFILIATIONS: Department of Resource Management and Geography, The University of Melbourne, Vic. 3010, Australia; 
School of Geography, Politics and Sociology, University of Newcastle, Daysh Building, Newcastle upon Tyne, NEI 7RU, United Kingdom; 
Jacobs, 1 City Walk, Leeds, West Yorkshire LS11 9DX, United Kingdom
ABSTRACT: The Kverkfjöll sandur in north Iceland is the furthest upstream of a suite of fluvial landforms extending for 200 km along the Jökulsá á Fjöllum river. Incision of the sandur exposes over 3 km of sedimentary sections, up to 15 m in height. A sandur wide, well-bedded succession of matrix-rich cobble-gravel and pebble/granule gravel, with individual beds 0.2 to 0.5 m thick indicates that the sandur is primarily the product of sandur-wide sheet-floods, with sediment-rich hyperconcentrated flows and also some debris flows and channelised turbulent flows. This interpretation is evidenced by bedded hyperconcentrated flow deposits occurring as laterally extensive tabular depositional units that dominate the entire sandur, reflecting the unconfined nature of the flow. Clast-supported boulder-gravel units interpreted as the product of macroturbulent flow occur in relatively narrow, but deep channels. The sedimentary succession is interpreted as the product of at least six volcanically generated catastrophic outburst floods (jökulhlaups) during the Little Ice Age. The sedimentology of these Little Ice Age flood deposits, on a small, high-gradient sandur, contrasts strongly with the deposits of volcanically-generated jökulhlaups on large, low-gradient coastal sandar, and sandar associated with retreating glaciers which have been the basis for most previous models of jökulhlaup sedimentation. © 2009 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Hyperconcentrated flows;  Proglacial sedimentology;  Volcaniclastic sediments
DOCUMENT TYPE: Article
SOURCE: Scopus

Melis, R., Salvi, G.
Late Quaternary foraminiferal assemblages from western Ross Sea (Antarctica) in relation to the main glacial and marine lithofacies
(2009) Marine Micropaleontology, 70 (1-2), pp. 39-53. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-58149316007&partnerID=40&md5=bef48d95cfa1ab8a65923f35855633d4
AFFILIATIONS: Department of Geological, Environmental and Marine Science, University of Trieste, via E. Weiss 2, 34127 Trieste, Italy
ABSTRACT: Investigations on foraminifers from Upper Pleistocene-Holocene sediments were carried out on twelve cores from the western Ross Sea continental margin (Drygalski, Joides, North Victoria Land Basins) as part of a "Progetto Nazionale di Ricerche in Antartide" (P.N.R.A.) multidisciplinary project. Data on the foraminiferal frequency, species diversity, tests abundance and their state of preservation were presented as a synthesis of 404 core samples to establish their relationships with the main glacial and marine lithofacies of this area. A total of 126 benthic species, pertaining to 73 genera have been identified; just few taxa, such as Cibicides spp., Globocassidulina spp., Trifarina angulosa and Miliammina spp. being the most ubiquitous and in some cases the dominant species of these paleoenvironments. Two variants of Neogloboquadrina pachyderma, including thin and thick-shelled forms have been recovered. We propose to use these results to provide the degree of glacial control during the Last Glacial Maximum and the following Holocene retreat of the ice sheets. High test fragmentation, low diversity and density tests reflect higher glacial influence of the ice sheet in the Drygalski Basin, whereas the decreasing percentage of fragmentation and a relative increase of density and diversity in Drygalski, Joides and North Victoria Land Basins indicate the paleoenvironmental passage from the ice sheet to the ice shelf condition. The ice shelf retreat is well evidenced in the Joides Basin by a succession of levels barren of foraminifers alternating with high-density levels, rich in T. angulosa, followed by a total disappearance of the calcareous foraminifers. Open-marine settings indicative of lower glacial influence and increased corrosiveness of the water masses is testified by the Miliammina foraminiferal assemblage during the Holocene in Drygalski and Joides Basins cores. On the contrary, rich and abundant benthic and planktonic assemblages characterize the Holocene paleoenvironment of the North Victoria Land area, indicating that the water masses were less corrosive with respect to the other areas. In addition to the glacial reworking of the tests, and the dissolution due to the corrosive water mass conditions, the volcaniclastic sediments recovered in the North Victoria Land Basin cores also affected the condition of test preservation. In volcaniclastic sediments, older than about 20 ka BP, the foraminifers concentration tends to zero and, when present, their tests are highly damaged or completely broken. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: foraminifers;  glacial influence;  glacial-marine and marine sediments;  taphonomy
DOCUMENT TYPE: Article
SOURCE: Scopus

Mariani, A.a , Bidali, S.a , Cappelletti, P.b , Caria, G.a , Colella, A.b , Brunetti, A.c  e , Alzari, V.a  d 
Frontal polymerization as a convenient technique for the consolidation of tuff
(2009) E-Polymers, art. no. 064, . 
http://www.scopus.com/inward/record.url?eid=2-s2.0-67651015615&partnerID=40&md5=2f2257dcacaee287367bfe498e60bccb
AFFILIATIONS: Dipartimento di Chimica, Università degli Studi di Sassari, Local INSTM research unit, Via Vienna 2, 07100 Sassari, Italy; 
Dipartimento di Scienze della Terra, Università Federico II, Via Mezzocannone 8, 80134 Naples, Italy; 
Dipartimento di Matematica e Fisica, Università di Sassari, Via Vienna 2, 07100 Sassari, Italy; 
Centro di Ingegneria dei Materiali, NIPLAB, Università di Perugia, Loc. Pentima Bassa, Terni, Italy; 
INFN, Sezione di Cagliari, Cagliari, Italy
ABSTRACT: Frontal Polymerization was successfully exploited as an innovative technique for the consolidation of Neapolitan Yellow Tuff, the main volcaniclastic rock of Campania region (Italy). The protocol used and the full characterization in terms of mechanical properties of the resulting consolidated stone are presented here and discussed together with the data obtained by X-ray tomography as a non destructive analytical technique for determining the internal map of the consolidated material. The proposed treatment definitely succeeded from the technical point of view resulting in an enhancement of mechanical properties.
DOCUMENT TYPE: Article
SOURCE: Scopus

le Friant, A.a , Deplus, C.a , Boudon, G.a , Sparks, R.S.J.b , Trofimovs, J.c , Talling, P.c 
Submarine deposition of volcaniclastic material from the 1995-2005 eruptions of Soufrière Hills volcano, Montserrat
(2009) Journal of the Geological Society, 166 (1), pp. 171-182. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69249186417&partnerID=40&md5=1ea25eb0866af22abb81e230db321a8f
AFFILIATIONS: Institut de Physique du Globe de Paris and CNRS, Case 89, 4 Place Jussieu, F-75252 Paris Cedex 05, France; 
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, United Kingdom; 
National Oceanography Centre, Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom
ABSTRACT: Soufrière Hills volcano, Montserrat, has been erupting since 1995. During the current eruption, a large part of the material produced by the volcano has been transported into the sea, modifying the morphology of the submarine flanks of the volcano. We present a unique set of swath bathymetric data collected offshore from Montserrat in 1999, 2002 and 2005. From 1999 to 2002, pyroclastic flows associated with numerous dome collapses entered the sea to produce 100 Mm3 deposit. From 2002 to 2005, the 290 Mm3 submarine deposit is mainly from the 12-13 July 2003 collapse. These data allow us to estimate that, by May 2005, at least 482 Mm3 of material had been deposited on the sea floor since 1995. We compare on-land characteristics and volumes of dome collapse events with the submarine deposits and propose a new analysis of their emplacement on the submarine flanks of the volcano. The deposition mechanism shows a slope dependence, with the maximum thickness of deposit before the break in the slope, probably because of the type of the dense granular flow involved. We conclude that from 1995 to 2005 more than 75% of the erupted volume entered the sea. © 2009 Geological Society of London.
DOCUMENT TYPE: Article
SOURCE: Scopus

Vezzoli, L.a , Matteini, M.b , Hauser, N.c , Omarini, R.c , Mazzuoli, R.d , Acocella, V.e 
Non-explosive magma-water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)
(2009) Bulletin of Volcanology, 71 (5), pp. 509-532. Cited 2 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649997312&partnerID=40&md5=1c3ab7429662e159360fc997b7cbbba4
AFFILIATIONS: Dipartimento Scienze Chimiche e Ambientali, Università dell'Insubria, Via Valleggio 11, Como 22100, Italy; 
Instituto de Geociencias, Universidade de Brasilia, Brasilia, Brazil; 
Facultad de Ciencias Naturales, Universidad Nacional de Salta-CONICET, Salta, Argentina; 
Dipartimento Scienze della Terra, Universitá di Pisa, Pisa, Italy; 
Dipartimento di Scienze Geologiche, Universitá di Roma Tre, Rome, Italy
ABSTRACT: The Middle-Upper Miocene Las Burras-Almagro-El Toro (BAT) igneous complex within the Eastern Cordillera of the central Andes (∼24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma) comprises facies related to: (i) andesite extruded in a subaqueous setting and generating lobe-hyaloclastite lava; and (ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water, comprising fluidal lava lobes, hyaloclastite, and juvenile clasts with glassy rims. The Lampazar member (7.8 Ma) is represented by a syn-volcanic andesite intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. The andesite intrusion is finger-shaped and grades into intrusive pillows. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment ≥50 m from the parent intrusion. The Almagro A member (7.2 Ma) shows evidence of mingling between water-saturated, coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and lobes with sharp contacts and fluidal shapes, and without quench fragmentation and formation of a hyaloclastite envelope. The presence of peperite and magma-water contact facies in the BAT volcanic sequence indicates the possible availability of water in the system between 11-7 Ma and suggests a depositional setting in this part of the foreland basin of the central Andes characterized by an overall topographically low coastal floodplain that included extensive wetlands. © Springer-Verlag 2008.
AUTHOR KEYWORDS: Central Andes;  Hyaloclastite;  Magma-water interaction;  Miocene volcanism;  Peperite;  Syn-volcanic intrusion;  Volcaniclastic succession
DOCUMENT TYPE: Article
SOURCE: Scopus

Schmincke, H.-U.a , Kutterolf, S.a , Perez, W.a , Rausch, J.a , Freundt, A.a , Strauch, W.b 
Walking through volcanic mud: The 2,100-year-old Acahualinca footprints (Nicaragua)
(2009) Bulletin of Volcanology, 71 (5), pp. 479-493. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649972448&partnerID=40&md5=471c8a088b8e5001a3f109ef16bc7c82
AFFILIATIONS: IFM-GEOMAR, Leibniz Institute of Marine Sciences, Wischhofstr. 1-3, Kiel 24148, Germany; 
INETER Instituto Nicaraguense de Estudios Territoriales, Managua, Nicaragua
ABSTRACT: We present the stratigraphy, lithology, volcanology, and age of the Acahualinca section in Managua, including a famous footprint layer exposed in two museum pits. The ca. 4-m-high walls of the main northern pit (Pit I) expose excellent cross sections of Late Holocene volcaniclastic deposits in northern Managua. We have subdivided the section into six lithostratigraphic units, some of which we correlate to Late Holocene eruptions. Unit I (1.2 m thick), chiefly of hydroclastic origin, begins with the footprint layer. The bulk is dominated by mostly massive basaltic-andesitic tephra layers, interpreted to represent separate pulses of a basically phreatomagmatic eruptive episode. We correlate these deposits based on compositional and stratigraphic evidence to the Masaya Triple Layer erupted at Masaya volcano ca. 2,120±12 a B.P. The eruption occurred during the dry season. A major erosional channel unconformity up to 1 m deep in the western half of Pit I separates Units II and I. Unit II begins with basal dacitic pumice lapilli up to 10 cm thick overlain by a massive to bedded fine-grained dacitic tuff including a layer of accretionary lapilli and pockets of well-rounded pumice lapilli. Angular nonvesicular glass shards are interpreted to represent hydroclastic fragmentation. The dacitic tephra is correlated unequivocally with the ca. 1.9-ka-Plinian dacitic Chiltepe eruption. Unit III, a lithified basaltic-andesitic deposit up to 50 cm thick and extremely rich in branch molds and excellent leaf impressions, is correlated with the Masaya Tuff erupted ca. 1.8 ka ago. Unit IV, a reworked massive basaltic-andesitic deposit, rich in brown tuff clasts and well bedded and cross bedded in the northwestern corner of Pit I, cuts erosionally down as far as Unit I. A poorly defined, pale brown mass flow deposit up to 1 m thick (Unit V) is overlain by 1-1.5 m of dominantly reworked, chiefly basaltic tephra topped by soil (Unit VI). A major erosional channel carved chiefly between deposition of Units II and I may have existed as a shallow drainage channel even prior to deposition of the footprint layer. The swath of the footprints is oriented NNW, roughly parallel to, and just east of, the axis of the channel. The interpretation of the footprint layer as the initial product of a powerful eruption at Masaya volcano followed without erosional breaks by additional layers of the same eruptive phase is strong evidence that the group of 15 or 16 people tried to escape from an eruption. © Springer-Verlag 2008.
AUTHOR KEYWORDS: Acahualinca footprints;  Erosional channeling;  Lake Managua;  Nicaragua;  Volcanic hazards
DOCUMENT TYPE: Article
SOURCE: Scopus

Frenz, M.a , Wynn, R.B.a , Georgiopoulou, A.b , Bender, V.B.c , Hough, G.a , Masson, D.G.a , Talling, P.J.d , Cronin, B.T.e 
Provenance and pathways of late Quaternary turbidites in the deep-water Agadir Basin, northwest African margin
(2009) International Journal of Earth Sciences, 98 (4), pp. 721-733. Cited 1 time.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67349236722&partnerID=40&md5=f4e279744afaaac6123440a6b658c9c1
AFFILIATIONS: National Oceanography Centre, European Way, Southampton, Hampshire SO14 3ZH, United Kingdom; 
School of Earth Ocean and Planetary Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, United Kingdom; 
Department of Sedimentology and Paleoceanography, University of Bremen, Klagenfurter Strasse, 28334 Bremen, Germany; 
Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, United Kingdom; 
Deep Marine, 9 North Square, Footdee, Aberdeen AB11 5DX, United Kingdom
ABSTRACT: A series of individual turbidites, correlated over distances >100 km, are present in the recent fill of the Agadir Basin, offshore northwest Africa. The aim here is to unravel multiple turbidite source areas and flow pathways, and show how turbidite provenance studies contribute to interpretation of flow processes. Agadir Basin turbidites are sourced from four main areas, with the majority originating from the siliciclastic Morocco Shelf; their sand-mud distribution is strongly controlled by flow sediment volume, with relatively low-volume flows dying out within the Agadir Basin and large-volume flows bypassing significant sediment volumes to basins further downslope. Two large-volume volcaniclastic turbidites are attributed to a Canary Islands landslide source, while several small mud-dominated turbidites are interpreted to be locally sourced from hemipelagic-draped seamounts (e.g. Turbidite AB10). Finally, Turbidite AB1 (μ1 ka) is only present in the western Agadir Basin, and is linked to recent "re-activation" of the Sahara Slide headwall. The muddy suspension clouds of three large-volume flows, all linked to large-scale landslides, have covered huge areas of seafloor and flowed along or even slightly upslope for long distances. It is proposed that northeastwards-flowing bottom currents have aided transport of these dilute flow fractions into and across the Agadir Basin. © Springer-Verlag 2008.
AUTHOR KEYWORDS: Agadir Basin;  Canary Islands;  Morocco Shelf;  Sediment provenance;  Turbidites
DOCUMENT TYPE: Article
SOURCE: Scopus

Maurice, C.a , David, J.b , Bédard, J.H.c , Francis, D.d 
Evidence for a widespread mafic cover sequence and its implications for continental growth in the Northeastern Superior Province
(2009) Precambrian Research, 168 (1-2), pp. 45-65. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-57849143706&partnerID=40&md5=e705e95ba76901a7683de4a9cc91b39e
AFFILIATIONS: Bureau de l'exploration géologique du Québec, Ministère des Ressources naturelles et de la Faune, 400 Boul. Lamaque, bureau 1.02, Val d'Or, Que. J9P 3L4, Canada; 
GEOTOP, UQAM-McGill, CP 8888, Succ. Centre-Ville, Montreal, Que., H3C 3P8, Canada; 
Geological Survey of Canada, GSC-Québec, 490 de la Couronne, Quebec, QC G1K 1A9, Canada; 
Earth and Planetary Sciences, McGill University, 3450 University St, Montréal, Que. H3A 2A7, Canada
ABSTRACT: Archean greenstone belts of the Northeastern Superior Province (NESP) were emplaced over a 160 Ma period (2.88-2.72 Ga), spanning a major episode of crustal reworking in which early tonalite-trondhjemite plutonism evolved to dominant granite-granodiorite and pyroxene-bearing felsic plutonism. The numerous greenstone belts that crop up across the craton contain lavas belonging to three mafic volcanic suites:(1)Mg-tholeiites that have chemical compositions typical of many Archean basalts, with 4-10 wt.% MgO, 9-15 wt.% Fe2O3t, 0.4-1.2 wt.% TiO2 and La/Sm ratios between 1 and 3.(2)Fe-tholeiites that have similar MgO contents and La/Sm ratios, but markedly higher Fe2O3t (11-20 wt.%), TiO2 (1.0-2.6 wt.%), and Gd/Yb ratios that may reflect derivation from a distinct garnet-bearing mantle source.(3)Light rare earth element (LREE)-enriched rocks that have the chemical characteristics typical of 'calc-alkaline' mafic magmas, with higher SiO2, Al2O3 and La/Sm ratios, but lower Fe2O3t and TiO2 than the tholeiitic suites at a given MgO content. The presence of unconformities within single greenstone belts, numerous inheritance ages in volcanic rocks replicating those of older volcanic-plutonic assemblages, and the recognition of widespread, geographically separate, yet coeval (2.78 Ga) extrusive assemblages containing the distinctive Fe-tholeiites, do not support a plate tectonic model for a large portion of the NESP. The correlations in composition and ages of greenstone belts are more consistent with a model in which they represent the remnants of an extensive autochthonous mafic cover sequence. Nd isotopic evidence for the presence of evolved crust in some syn-volcanic felsic plutons and volcaniclastic rocks imply that this mafic cover sequence was erupted onto an older granitoid crust. The amalgamation of two isotopically distinct terranes at ca. 2.76-2.74 Ga created a proto-cratonic mass that consisted of a composite tonalite-trondhjemite-greenstone crust. Underplating by mafic mantle melts and widespread insulation after 2.75 Ga increased temperatures sufficiently to produce extensive melting of this crust to generate pyroxene-bearing felsic rocks and granodiorite to granite partial melts. The isotopically enriched character of mantle-derived magmas after 2.75 Ga may reflect more extensive contamination by a felsic crust affected by widespread partial melting. Furthermore, a decrease of Nb/Th ratios in the LREE-enriched mafic rocks younger than 2.75 Ga reflects a change in the nature of the crustal contaminant, from tonalite-trondhjemite prior to 2.75 Ga, to granite-granodiorite afterwards. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Archean;  Continental growth;  Geochemistry;  Greenstone belts;  Northeastern Superior Province
DOCUMENT TYPE: Article
SOURCE: Scopus

Wu, X.a , Liu, D.a , Li, J.b , Sun, X.c 
Reservoir properties and controlling factors of Carboniferous volcanic rocks in Ludong-Wucaiwan area of the Junggar Basin
(2009) Scientia Geologica Sinica, 44 (1), pp. 1-13. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-67649274447&partnerID=40&md5=0d6263e5ce7bbf603cea5d632c968388
AFFILIATIONS: School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026; 
Langfang Branch, Research Institute of Petroleum Exploration and Development of China, Langfang, Hebei 065007; 
Institute of Geological Experiment of Anhui Province, Hefei 230001
ABSTRACT: The study on volcanic pools and their oil-gas exploration of the Carboniferous volcanic rocks in Ludong-Wucaiwan area of the Junggar Basin made an important progress recently. The volcanic rocks were mainly composed of intermediate-basic lavas and intermediate-acidic volcaniclastic rocks. The reservoir space of volcanic rocks could be divided into primary pores and secondary pores, and the reservoir properties were mainly affected by lithology and lithofacies, weathering and secondary solution, tectonism, environment of formation. The most favorable reservoir rocks in the studied area were volcaniclastic rocks and rhyolites, and the secondary favorable one was andesites, and the most favorable reservoir position was weatherd crust at the top of the Carboniferous. There were regional variations in types of volcanic rocks, reservoir properties of volcanic rocks as well as rock association types of reservoir space. The volcanic rocks in Ludong area were the most favorable reservoirs, the volcanic rocks in Wucaiwan area were relatively good ones, and the reservoir properties might be poor of the rocks in Sangequan area.
AUTHOR KEYWORDS: Carboniferous volcanic rocks;  Permeability;  Porosity;  Reservoir space;  The Junggar Basin
DOCUMENT TYPE: Article
SOURCE: Scopus

Pearson, V.a , Daigneault, R.b 
An Archean megacaldera complex: The Blake River Group, Abitibi greenstone belt
(2009) Precambrian Research, 168 (1-2), pp. 66-82. Cited 4 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-57749205716&partnerID=40&md5=0d14ebe309a0d330b1d58d345fddc102
AFFILIATIONS: CONSOREM - Consortium de recherche en exploration minérale, 555 Boul. de l'Université, Chicoutimi, G7H 2B1, Canada; 
Centre d'etudes sur les Ressources minerales (CERM) - Universite du Quebec a Chicoutimi, 555 Boul. de l'Université, Chicoutimi, G7H 2B1, Canada
ABSTRACT: The Archean Blake River Group of the southern Abitibi greenstone belt is defined as a subaqueous megacaldera. Compelling evidence include: (1) a radial and concentric organization of synvolcanic mafic to intermediate dykes, (2) an overall dome geometry defined by the volcanic strata, (3) a peripheral distribution of subaqueous volcaniclastic units, (4) a zonal distribution of carbonate alteration, and (5) a distinct annular synvolcanic inner and outer ring fault pattern. Three caldera-forming events have been identified: (1) the early Misema caldera, (2) the New Senator caldera, and (3) the well-known Noranda caldera. The multi-vent BRG mafic volcanic complex, developed on a monotonous sequence of tholeiitic basalts, forming a submarine plain, and experienced a first major collapse that created the giant Misema Caldera (80 km in diameter). An endogenic dyke swarm intruded the synvolcanic fractures and an underlying magma chamber developed. Major volcaniclastic units were generated by local volcanic centers and summit calderas formed along the outer and inner ring faults. This fault system was used as a conduit for CO2-rich hydrothermal activity. Renewed volcanic activity was associated with a resurgent central dome inside the Misema Caldera. This second collapse event created the 35 km by 14 km NW-trending New Senator Caldera. This caldera was produced by multi-step sagging after the underlying magmatic chamber migrated to the SE and formed the Flavrian-Powel Plutons. The final collapse resulted in the formation of the Noranda Caldera that generated a well-developed 070°-trending fracture pattern associated with several VMS deposits. The multiple-caldera setting provides an effective model to explain the presence of VMS mineralization along the synvolcanic fractures associated with the three collapse episodes. However, the importance of the New Senator Caldera fracture pattern is emphasized because of its role in the positioning of the giant Horne Mine deposit. © 2008 Elsevier B.V. All rights reserved.
AUTHOR KEYWORDS: Abitibi greenstone belt;  Archean;  Blake River Group;  Caldera;  Greenstone belt;  VMS deposits
DOCUMENT TYPE: Article
SOURCE: Scopus

Brown, R.J.a , Tait, M.b , Field, M.a , Sparks, R.S.J.a 
Geology of a complex kimberlite pipe (K2 pipe, Venetia Mine, South Africa): Insights into conduit processes during explosive ultrabasic eruptions
(2009) Bulletin of Volcanology, 71 (1), pp. 95-112. Cited 6 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-57849139802&partnerID=40&md5=ea1c6fc5965e1d833a6102d5de66383e
AFFILIATIONS: Department of Earth Sciences, Wills Memorial Building, University of Bristol, Queen's Road, Bristol BS8 1RJ, United Kingdom; 
De Beers Group Services, Cornerstone Office, Southdale 2135, Johannesburg, South Africa
ABSTRACT: K2 is a steep-sided kimberlite pipe with a complex internal geology. Geological mapping, logging of drillcore and petrographic studies indicate that it comprises layered breccias and pyroclastic rocks of various grain sizes, lithic contents and internal structures. The pipe comprises two geologically distinct parts: K2 West is a layered sequence of juvenile- and lithic-rich breccias, which dip 20-45° inwards, and K2 East consists of a steep-sided pipe-like body filled with massive volcaniclastic kimberlite nested within the K2 pipe. The layered sequence in K2 West is present to > 900 m below present surface and is interpreted as a sequence of pyroclastic rocks generated by explosive eruptions and mass-wasting breccias generated by rock fall and sector collapse of the pipe walls: both processes occurred in tandem during the infill of the pipe. Several breccia lobes extend across the pipe and are truncated by the steep contact with K2 East. Dense pyroclastic rocks within the layered sequence are interpreted as welded deposits. K2 East represents a conduit that was blasted through the layered breccia sequence at a late stage in the eruption. This phase may have involved fluidisation of trapped pyroclasts, with loss of fine particles and comminution of coarse clasts. We conclude that the K2 kimberlite pipe was emplaced in several distinct stages that consisted of an initial explosive enlargement, followed by alternating phases of accumulation and ejection. © Springer-Verlag 2008.
AUTHOR KEYWORDS: Explosive eruption;  Kimberlite;  Pyroclastic;  Volcanic conduit
DOCUMENT TYPE: Article
SOURCE: Scopus

Lin, W.a , Faure, M.b , Shi, Y.c , Wang, Q.a , Li, Z.a 
Palaeozoic tectonics of the south-western Chinese Tianshan: New insights from a structural study of the high-pressure/low-temperature metamorphic belt
(2009) International Journal of Earth Sciences, 98 (6), pp. 1259-1274. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-69849097328&partnerID=40&md5=083ed985101152ec5d01330f545f718c
AFFILIATIONS: SKL, Institute of Geology and Geophysics, Chinese Academy of Sciences, P. O. Box 9825, 100029 Beijing, China; 
ISTO, UMR-CNRS 6113, Université d'Orléans, 45067 Orléans Cedex 2, France; 
Department of Geology, School of Resource and Environment Engineering, Hefei University of Technology, Tunxi Road 193, Hefei Anhui 230009, China
ABSTRACT: The south-western Chinese Tianshan orogenic belt is famous for its omphacite-bearing blueschists and associated eclogite-facies metavolcanic rocks. Although numerous petrologic, geochemical and geochronological studies are available, structural data and interpretations are still rare. This paper provides new structural data, including bulk geometry of structures and kinematic analyses, based on field and laboratory studies along the Akyazhi, Keburt and Muzaert Rivers. The study area is divided into three tectonic units, namely (1) a Southern Unit composed of weakly metamorphosed sedimentary rocks of Silurian age; (2) a Central HP/LT Unit composed of blueschist-eclogite-facies metamorphic rocks derived from basalts, pelites and volcaniclastic rocks; (3) a Northern Unit, which consists of a Carboniferous magmatic arc developed upon an amphibolite-facies metamorphic continental basement. Our structural analysis documents a polyphase deformation. The main event (D1) is reflected by Devonian to Carboniferous top-to-the northwest ductile shearing, coeval with HP/LT metamorphism. This is followed by north-directed thrusting (D2) of the Southern Unit over the Central HP/LT Unit, coeval with retrogression of the high-pressure rocks. A top-to-the-S (SE) deformation (D3) overprints the earliest events and is observed in the Northern and Central Units. Lastly, Permian dextral ductile-brittle wrenching (D4) overprints the older flat-lying fabrics. D4 is conspicuous along the Nalati Fault that separates the Northern Unit from the Central HP/LT Unit. The absolute timing of these deformation events is discussed in the light of available radiometric dating. The structural, metamorphic and geochronological data are integrated into a geodynamic model of the south-western Chinese Tianshan that emphasizes south-directed subduction of microcontinents located between Tarim and Junggar. © Springer-Verlag 2008.
AUTHOR KEYWORDS: Chinese Tianshan;  HP metamorphism;  Palaeozoic geodynamics;  Polyphase deformation;  Structural analysis
DOCUMENT TYPE: Conference Paper
SOURCE: Scopus

Cavazza, W.a , Okay, A.I.b , Zattin, M.a 
Rapid early-middle Miocene exhumation of the Kazdaǧ Massif (western Anatolia)
(2009) International Journal of Earth Sciences, 98 (8), pp. 1935-1947. Cited 5 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-70350619373&partnerID=40&md5=34eefc6c856d3045cb067874890a02fa
AFFILIATIONS: Department of Earth and Geoenvironmental Sciences, University of Bologna, 40126 Bologna, Italy; 
Eurasia Institute of Earth Sciences, Istanbul Technical University, 34469 Istanbul, Maslak, Turkey
ABSTRACT: Apatite fission-track analyses indicate that the Kazdaǧ Massif in northwestern Anatolia was exhumed above the apatite partial annealing zone between 20 and 10 Ma (i.e. early-middle Miocene), with a cluster of ages at 17-14 Ma. The structural analysis of low-angle shear zones, high-angle normal faults and strike-slip faults, as well as stratigraphic analysis of upper-plate sedimentary successions and previous radiometric ages, point to a two-stage structural evolution of the massif. The first stage -encompassing much of the rapid thermal evolution of the massif- comprised late Oligocene-early Miocene low-angle detachment faulting and the associated development of small supradetachment grabens filled with a mixture of epiclastic, volcaniclastic and volcanic rocks (Küçükkuyu Fm.). The second stage (Plio-Quaternary) has been dominated by (i) strike-slip faulting related to the westward propagation of the North Anatolian fault system and (ii) normal faulting associated with present-day extension. This later stage affected the distribution of fission-track ages but did not have a component of vertical (normal) movement large enough to exhume a new partial annealing zone. The thermochronological data presented here support the notion that Neogene extensional tectonism in the northern Aegean region has been episodic, with accelerated pulses in the early-middle Miocene and Plio-Quaternary. © Springer-Verlag 2008.
AUTHOR KEYWORDS: Aegean Sea;  Detachment fault;  Fission-track analysis;  North Anatolian fault system;  Thermochronology
DOCUMENT TYPE: Article
SOURCE: Scopus

Olivero, E.B.a , Medina, F.A.b , López C., M.I.a 
The stratigraphy of Cretaceous mudstones in the eastern Fuegian Andes: New data from body and trace fossils [Estratigrafía de las fangolitas del Cretácico en los Andes Fueguinos orientales: Nuevos datos de cuerpos y trazas fósiles]
(2009) Revista de la Asociacion Geologica Argentina, 64 (1), pp. 60-69. Cited 3 times.
http://www.scopus.com/inward/record.url?eid=2-s2.0-68949192984&partnerID=40&md5=7de55e105a1de8b43e9b90f3dd9b50d9
AFFILIATIONS: Centro Austral de Investigaciones Científicas (CADIC-CONICET), B.A. Houssay 200, 9410 Ushuaia, Tierra del Fuego, Argentina; 
Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, UBA, Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA Buenos Aires, Argentina
ABSTRACT: The stratigraphy of Cretaceous marine mudstones in the Fuegian Andes, roughly equivalent to Charles Darwin's clay-slate formation, remains a still unsolved problem. Previous records of Albian, Turonian-Coniacian, and Santonian-Campanian bivalves are combined with new findings of the Late Albian inoceramid Inoceramus anglicus Woods, and the Maastrichtian ammonites Diplomoceras sp., Anagaudryceras sp., Maorites densicostatus (Kilian and Reboul), Maorites sp., and Pachydiscus (Neodesmoceras) sp. to further constrain the Cretaceous stratigraphy of the eastern Fuegian Andes. In addition, new records of distinctive trace fossils and ichnofabric are meaningful for stratigraphic division and delineation of paleoenvironmental settings in these Cretaceous mudstones. The Lower Cretaceous ichnoassemblage of Chondrites targioni (Brongniart) and Zoophycos isp. is consistent with the inferred slope-volcaniclastic apron settings of the Yahgan Formation; Nereites missouriensis (Weller) reflects distal basin plain depositional settings for the Beauvoir Formation. In the Upper Cretaceous, the "Estratos de Buen Suceso" record the earliest extensively bioturbated horizons, reflecting prolonged well-oxygenated bottom conditions. In the Bahía Thetis Formation, organic-rich, channel margin or distal basin slaty mudstones record the last occurrence of inoceramid bivalves in the Austral Basin; the generalized absence of trace fossils is consistent with dysoxic bottom conditions. The thoroughly bioturbated Policarpo Formation, records a marked change in paleoceanographic conditions. The strong contrast in the intensity of bioturbation between the Upper Campanian-Maastrichtian Bahía Thetis Formation, almost devoid of trace fossils, and the highly bioturbated Maastrichtian-Danian Policarpo Formation reflects a change from dysoxic-anoxic to well ventilated conditions, probably associated with a cooling trend of bottom waters in the austral deep oceans.
AUTHOR KEYWORDS: Ammonites;  Clay-slate formation;  Cretaceous;  Fuegian andes;  Inoceramid;  Trace fossils
DOCUMENT TYPE: Article
SOURCE: Scopus

Brea, M.a  d , Artabe, A.E.b  d d  , Spalletti, L.A.c  d d  
Darwin forest at Agua de la Zorra: The first in situ forest discovered in South America by Darwin in 1835 [El Bosque Darwin en Agua de la Zorra: El primer bosque in situ descubierto en América del Sur por Darwin en 1835]
(2009) Revista de la Asociacion Geologica Argentina, 64 (1), pp. 21-31. 
http://www.scopus.com/inward/record.url?eid=2-s2.0-68949175667&partnerID=40&md5=22ff39ec2ae3c23354ddb974a427ed42
AFFILIATIONS: Laboratorio de Paleobotánica, Centro de Investigaciones Científicas, Diamante. CICYTTP-Diamante, Consejo Nacional de Investigaciones Científicas y Técnicas, Diamante, Entre Ríos, Argentina; 
División Paleobotánica, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina; 
Centro de Investigaciones Geológicas (CONICET-UNLP), La Plata, Argentina; 
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
ABSTRACT: The Agua de la Zorra area (near Uspallata, Mendoza, Argentina) is one of the best renowned fossil localities of the country because of its spectacular in situ fossil forest. This forest was discovered by Charles Darwin in 1835, who described this forest as monotypic and assigned it a Tertiary age. Nowadays, this fossil locality is known as the Darwin Forest. Over a century and a half later it was reinterpreted as a mixed Middle Triassic forest and a new fossil monotypic palaeocommunity of horsetails was discovered. This palaeovegetation is included in the Paramillo Formation (i.e., lower section the Potrerillos Formation) of northwestern Cuyo Basin, Mendoza province (69°12' W and 32°30' S). The sediments were deposited in a sinuous fluvial system, in which channel-filling sand bodies were associated with mud-dominated floodplain deposits. The palaeoforest grew on an andisol soil that developed on volcaniclastic floodplain deposits. It had a density of 427 -759 trees per hectare, and was constituted by conifers and corystosperms distributed in two arboreal strata. The highest reached 20-26 m tall, and was dominated by corystosperms, but it also included the tallest conifers. The second stratum, mainly composed of conifers, ranged between 16-20 m tall. The forest has also emergent corystosperms, which reached 30 m tall. The understorey was composed of ferns. Growth ring anatomy suggests that conifers could have had an evergreen habit. Structure of vegetation, growth ring analyses and sedimentation suggest that the forest developed under dry, subtropical, and strongly seasonal conditions.
AUTHOR KEYWORDS: Middle triassic;  Palaeoecology;  Palaeoenvironments;  Palaeovegetation;  Southwestern gondwana
DOCUMENT TYPE: Article
SOURCE: Scopus