New Zealand Journal of Geology and Geophysics abstracts

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Granitoids of the Dry Valleys area, southern Victoria Land: geochemistry and evolution along the early Paleozoic Antarctic Craton margin

ANDREW H. ALLIBONE

Department of Geology
James Cook University of North Queensland
Townsville, Q4811, Australia*

SIMON C. COX
ROBERT. W. SMILLIE

Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand

*Present address: Etheridge and Henley Geoscience Consultants, P.O. Box 3778, Manuka, A.C.T 2603, Australia.

Abstract Field relationships and geochemistry indicate granitoid plutons of the Dry Valleys area comprise at least three petrogenetically distinct suites. The older Dry Valleys la (DVla) suite, comprising the Bonney, Catspaw, Denton, Cavendish, and Wheeler Plutons and hornblende-biotite orthogneisses, and Dry Valleys lb (DVlb) suite, comprising the Hedley, Valhalla, St Johns, Dun, Calkin, and Suess Plutons, biotite granitoid dikes and biotite orthogneisses, were emplaced before prominent swarms of Vanda mafic and felsic dikes. Both the DVla and DVlb suites are time transgressive, with older intrusions in each suite being emplaced during the later stages of deformation of the Koettlitz Group. Younger granitoids that postdate the majority of the Vanda dikes include: the Dry Valleys 2 (DV2) suite, comprising the Pearse and Nibelungen Plutons plus several smaller, unnamed plugs; and the Harker, Swinford, Orestes, and Brownworth Plutons with identical field relationships and enclaves but distinct chemistries.
Chemical characteristics and limited Rb-Sr isotopic dating indicate plutonism before c. 500 Ma was dominated by the Cordilleran I-type DVla suite, inferred to have developed during melting above a west-dipping subduction zone along the Antarctic Craton margin. The chemical characteristics of the DVlb suite indicate large-scale melting of a quartzo-feldspathic protolith lacking residual plagioclase, but containing refractory garnet. Potential DVlb suite source rocks include metamorphosed immature sediments, possibly underplated along the subduction zone associated with DVla magmatism, or older granitoid orthogneisses. Major DVlb plutonism at 490 Ma marks the end of subduction-related plutonism in southern Victoria Land. Younger DV2 alkali-calcic, Caledonian I-type plutonism is inferred to have formed in response to uplift and extension between 480 and 455 Ma. Lack of DV2 suite correlatives and Vanda mafic and felsic dikes in northern Victoria Land suggests significantly different tectonomagmatic histories along the early Paleozoic Antarctic Craton margin.

Keywords geochemistry; granitoids; plutons; suites; petrogenesis; southern Victoria Land; Antarctica; Dry Valleys

Received 2 June 1992; published 14 September 1993
New Zealand Journal of Geology & Geophysics, 1991, Vol. 36: 299—316
0028Ð8306/06/3603—0299 ©The Royal Society of New Zealand 1991

PDF file of entire paper: medium quality (2040K); (scanned from paper original: notes about this process). Digitisation of this article from the printed journal was kindly facilitated by the Geological Society of New Zealand

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