Dr Stephen Read
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BSc(Hons) | DipGrad | PhD (Otago) |
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PhD thesis: Koettlitz Glacier Alkaline Province: Late Neoproterozoic extension in southern Victoria Land, Antarctica.
Abstract
The Koettlitz Glacier Alkaline Province, in southern Victoria Land, Antarctica, is characterised by Late Neoproterozoic, extension-related plutonism. Stretching 100 kilometres along the Hillary Coast from the Radian Glacier, in the north, to the Mulock Glacier, in the south, the Koettlitz Glacier Alkaline Province is exposed over at least 2000 km2.
The oldest intrusions dated during this study are mafic members of the Glee Intrusives, a suite ranging from 46 wt% SiO2 alkaline gabbros to 68 wt% SiO2 quartz monzonites that crop out in the north of the studied area, between the Kempe and Panorama Glaciers. Enriched in Ti, Fe, Mn, K, P & Ba, the Glee Intrusives are borderline subalkaline/alkaline, metaluminous, calc-alkalic/alkali-calcic, transitional basalts and derivatives. Initial epsilon Nd (-2.58) and initial 87Sr/86Sr (0.708) values are more primitive than most nearby intrusions, indicating lesser crustal input in the Glee Intrusives. Zircon ages of 553 ± 5 Ma & 550 ± 5 Ma date emplacement, while titanite ages of 538 ± 2 Ma & 534 ± 1 Ma date subsequent deformation then cooling. Geochemical characteristics of the Glee Intrusives imply emplacement into a failed intra-continental rift. The alkaline gabbroic components of the Glee Intrusives are geochemically equivalent to alkaline components of the nearby Panorama Pluton and Dromedary Mafic Complex.
The Skelton Mafic Suite, which crops out on both sides of the Skelton Glacier in the vicinity of Cocks Bluff, ranges from magnesian, calcic, 48 wt% SiO2 gabbros to ferroan, calc-alkalic, 59 wt% SiO2 monzonites. This array is a result of fractional crystallisation from a gabbroic end member such as sampled at Breezy Bluff, one kilometre northeast of Cocks Bluff. Zircon and titanite from the Skelton Mafic Suite have been dated at 548 ± 2 Ma and 547 ± 4 Ma, respectively, indicating emplacement at this time. The subalkaline Skelton Mafic Suite is part of a broader mafic association within the Koettlitz Glacier Alkaline Province that contains both subalkaline and alkaline components. This association includes the Panorama Pluton (557 ± 5 Ma) and the Dromedary Mafic Complex. The outcrop characteristics and geochemical nature of these subalkaline-alkaline mafic intrusions indicate emplacement in a transitional compressional / extensional tectonic setting.
The most characteristic suite in the Koettlitz Glacier Alkaline Province is the Hillary Suite that comprises high-silica, A2 group, A-type granitoids and subordinate syenites. Members of the Hillary Suite are enriched in Si, Fe, Na, K, Ga, Nb, La, Nd, Rb, Y, Pb, Th & U and depleted in Al, Mg, Ca, Ba & Sr. Strong enrichment in REE, particularly the LREE (LaN/LuN=5-40), and large negative Eu anomalies (Eu/Eu*=0.04-0.53) are apparent in all samples. The Sm-Nd & Rb-Sr isotopic character of the Hillary Suite (initial epsilon Nd = -4.5 to –7.5 and initial 87Sr/86Sr 0.708-0.710) suggests derivation from crustal rather than mantle source rocks. New Hillary Suite emplacement ages of 550 ± 3 Ma, 548 ± 4 Ma, 546 ± 3 Ma, 546 ± 3 Ma and 542 ± 3 Ma are all Late Neoproterozoic. The geochemical nature, geographic spread and emplacement ages of the Hillary Suite indicate that the Koettlitz Glacier Alkaline Province was the site of broad crustal extension during the Late Neoproterozoic.
The extension and distinctive alkaline magmatism that occurred in the Koettlitz Glacier Alkaline Province from 557-542 Ma is unreported from elsewhere along the Transantarctic Mountains. Outside the Koettlitz Glacier Alkaline Province the oldest dated intrusions are younger, and related to convergence and subduction rather than extension.
Following the broad crustal extension that resulted in the emplacement of the Glee Intrusives, the Hillary Suite, the Skelton Mafic Suite, and correlatives during the interval 557-542 Ma, there was a period of deformation that resulted in the resetting of many U-Pb geochronometers, particularly in the northern Koettlitz Glacier Alkaline Province. Reset ages range from 538 ± 2 Ma to 534 ± 1 Ma.
Post-dating the extension and subsequent deformation, the Hooper Suite is a characteristic group of undeformed, 60-75 wt% SiO2, granitoids enriched in Sr, Al, Mg, Ca & Ba and depleted in K, La, Ce, Nd, Y, Zr, Th & HREE. These characteristics, combined with moderately radiogenic Nd & Sr isotopic ratios (initial epsilon Nd = -5.65, -10.95 and initial 87Sr/86Sr 0.707, 0.711), indicate derivation via water-undersaturated partial melting of underplated basaltic rock beneath thickened crust. The Hooper Suite was emplaced at 533 ± 3 Ma & 524 ± 4 Ma in the southern Skelton Glacier area, at 520 ± 4 Ma at Hooper Crags, in the middle of the Koettlitz Glacier Alkaline Province, and at 515 ± 4 Ma & 511 ± 3 Ma in the north, just south of the Radian Glacier. The ages and locations of these intrusions describe a northward younging of 22 million years over a distance of 80 kilometres.
All of these events occurred in the Koettlitz Glacier Alkaline Province prior to the onset of voluminous subduction-related Ross Orogeny magmatism at ca. 505 Ma in adjacent areas north of the Koettlitz Glacier Alkaline Province.
Maps
The Koettlitz Glacier Alkaline Province (red box centred at 162ºE, 78º40’S) is located in the southern Victoria Land segment of the Transantarctic Mountains that border the East Antarctic Craton. Areas of outcrop (excluding young northern Victoria Land terranes and McMurdo Volcanics) are shown in black. An enlargement of the Koettlitz Glacier Alkaline Province is shown in the map below.
The Koettlitz Glacier Alkaline Province extends from the Radian Glacier in the north to the Mulock Glacier in the south – a distance of 100 km. Hillary Suite (yellow) and Hooper Suite (blue) crop out throughout. The Glee Intrusives (red) are restricted to the north while the Moraine Bluff Suite (green) and Skelton Mafic Suite (black) crop out only in the Skelton Glacier area. Other outcrop is shown in grey.
Funding
- Research - University of Otago Research Grant through supervisor
- Personal - University of Otago Postgraduate Scholarship, inaugural Sir Robin Irvine Antarctic Scholarship (shared)
Publications
Refereed Papers
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Veevers, J. J, Belousova, E. A, Saeed, A, Sircombe, K, Cooper, A. F, Read, S. E, . Elsevier Science; 2006. Pan-Gondwanaland detrital zircons from Australia analysed for Hf-isotopes and trace elements reflect an ice-covered Antarctic provenance of 700-500 Ma age, TDM of 2.0-1.0 Ga, and alkaline affinity.
- Read, S.E., Cooper, A.F., and Walker, N.W., 2002. Geochemistry and U-Pb geochronology of the Neoproterozoic-Cambrian Koettlitz Glacier Alkaline Province, Royal Society Range, Transantarctic Mountains, Antarctica. 8th International Symposium on Antarctica Earth Sciences, The Royal Society of New Zealand Bulletin 35.
Conferences (more details)
8th International Symposium on Antarctic Earth Sciences, Wellington, New Zealand, 1999.
Read, S.E., Cooper, A.F., Walker, N.W., 1999. Geochemistry and U-Pb geochronology of the Neoproterozoic-Cambrian Koettlitz Glacier Alkaline Province, Royal Society Range, Transantarctic Mountains, Antarctica. 8th International Symposium on Antarctic Earth Sciences, Wellington, New Zealand.
Geological Society of New Zealand annual conference, Hamilton, New Zealand, 2001.
Read, SE, 2001. Hillary Granitoids of the Koettlitz Glacier Alkaline Province, Antarctica. Geological Society of New Zealand, Annual Conference.
Read, SE, Simpson, A.L., Cottle, J.M. 2001. Adakitic magmatism in the Koettlitz Glacier Alkaline Province, southern Victoria Land, Antarctica. Geological Society of New Zealand, Annual Conference. poster
Annual Antarctic Conference, April 2003, Dunedin, New Zealand
Read, S.E., Cooper, A.F., Cottle, J.M, Palin, J.M, Wynyard, M.J., 2003. Early extension in a convergent margin, Skelton Glacier, Antarctica. poster