John Cottle
Current Address
Department of Earth Science
University of California
Santa Barbara CA 93106-9630
email: cottle@geol.ucsb.edu
web: http://www.geol.ucsb.edu/faculty/cottle
MSc thesis title
Evolution of a Convergent Margin - a Petrological study of Ross Orogeny Magmatism in the Carlyon Glacier Region, southern Victoria Land, Antarctica. 2002
Supervisor
Publications
- Cottle, J.M., & Cooper, A.F. 2006: The Fontaine Pluton: an early calc-alkaline gabbro from southern Victoria Land, Antarctica. New Zealand Journal of Geology & Geophysics v.49(2) p.177-189
- Cottle, J.M., & Cooper, A.F. 2006: Geology, geochemistry and geochronology of an A-type granite in the Mulock Glacier Area, southern Victoria land, Antarctica. New Zealand Journal of Geology & Geophysics v.49(2) p.191-202
- Cottle, J.M. 2002: Evolution of a Convergent Margin - a Petrological study of Ross Orogeny Magmatism in the Carlyon Glacier Region, southern Victoria Land, Antarctica. Unpublished M.Sc. Thesis lodged in the University of Otago Library.
MSc abstract
The Fontaine Pluton outcrops over an area of 0.5km2 at Fontaine Bluff in the Carlyon Glacier area of southern Victoria Land, Antarctica. The pluton comprises subalkaline gabbro with a distinctive calc-alkaline chemical affinity. Thermobarometry indicates emplacement occurred at 4kbar pressure and at a minimum temperature of 710 ± 21°C. U-Pb isotopic systematics of zircon suggest an emplacement age for the pluton of 544 ± 10 Ma. Geochemistry, geochronology and Sr-Nd isotope systematics indicate that the Fontaine Pluton has close affinities with other mafic plutons in the Royal Society Range to Skelton Glacier area of southern Victoria Land. The pluton contains numerous ultramafic xenoliths inferred to be remnants of an earlier intrusive phase.
The previously undescribed Cape Murray and North Carlyon granitoids are calc-alkaline, K- series, I-type, volcanic arc intrusives. Zircon from the Cape Murray granodiorite yields a U-Pb date of 548 ± 2.5 Ma. This places the Cape Murray rock as the oldest Ross Orogeny calc-alkaline granitoid yet described from the Transantarctic Mountains.
Calc-alkaline lamprophyres and tholeiitic amphibolite dikes post-date calc-alkaline granitoid emplacement. These dikes formed as a result of mantle melting that was synchronous with, or immediately post-dated subduction. In terms of both geochemistry and age the dikes appear not to have correlatives elsewhere in southern Victoria Land.
Granitoids with adakitic affinities crop out on the south side of the Carlyon Glacier. U-Pb isotope systematics of zircon and titanite indicate that the adakite at south Fontaine Bluff crystallised at 491 ± 3.3 Ma. Adakitic plutonism is inferred to be the result of partial melting of a mafic underplate beneath a thickened continental root. The emplacement of these relatively voluminous magmas is interpreted to post-date subduction in this area of southern Victoria Land.
The Mulock Granite is a previously undescribed A-type intrusion that outcrops on the north side of the Mulock Glacier. U-Pb geochronology on zircon indicates an emplacement age of 546 ± 3 Ma, coeval with A-type granitoids in the Skelton Glacier area. Emplacement of the Mulock Granite post-dates deformation and metamorphism of the host Skelton Group calc-silicate metasediments.
The Carlyon Glacier area represents a distinct magmatic province within the Ross Orogen of the Transantarctic Mountains. Magmatism was initiated within a convergent margin setting at ca. 548 Ma as recorded by the emplacement of calc-alkaline granitoid and mafic magmas. Continued subduction produced calcic and calc-alkaline granitoids which appear to have a petrologically unique association with A-type granites. Emplacement of voluminous calc-alkaline magmas caused significant crustal thickening, this, combined with mafic underplating enabled the production of widespread adakitic magmas between ca. 515 Ma and ca. 491 Ma.
Subduction related plutonism in the Carlyon Glacier area pre-dates ca. 90% of magmatic activity in the Dry Valleys area but appears to be broadly synchronous with alkaline magmatism in the Walcott to Mulock Glacier region and calc-alkaline granitoid magmatism in the central Transantarctic Mountains.