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Granites of Edward VII Peninsula, Marie Byrd Land: anorogenic magmatism related to Antarctic-New Zealand rifting

Published online by Cambridge University Press:  03 November 2011

S. D. Weaver
Affiliation:
S. D. Weaver, Department of Geology, University of Canterbury, Christchurch, New Zealand
C. J. Adams
Affiliation:
C. J. Adams, Department of Scientific and Industrial Research, Physical Sciences, Lower Hutt, New Zealand
R. J. Pankhurst
Affiliation:
R. J. Pankhurst, British Antarctic Survey, c/o Natural Environment Research Council, Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, U.K.
I. L. Gibson
Affiliation:
I. L. Gibson, Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada

Abstract

Syenogranites and monzogranites of Edward VII Peninsula, Marie Byrd Land, represent magmatism associated with continental rifting and the separation of New Zealand from W Antarctica in the mid-Cretaceous. These coarse-grained, leucocratic, subsolvus biotite granites occur as five small plutons cutting Lower Palaeozoic metasediments. Petrographic features include the predominance of microcline perthite over albite, bipyramidal smoky quartz, red-brown biotite and accessory ilmenite, zircon, apatite, monazite and fluorite. Enclaves are absent and miarolitic cavites are rare.

The granites are a weakly peraluminous, potassic, and highly fractionated suite with high concentrations of Rb, Nb, Y, HREE and F in the most evolved compositions. REE patterns vary from LREE-enriched (CeN/YbN = 8·4), to flat REE patterns (CeN/YbN = 1·1) with large negative Eu anomalies (Eu/Eu* = 0·02). Initial 87Sr/86Sr ratios are 0·7116-0·7206 and initial εNd values are −5·5 to −7·7. Generalised fractionation trends for the suite are explicable in terms of the modal mineralogy. Monazite crystallisation exerted a predominant control on LREE concentrations.

The geochemistry of the Edward VII Peninsula granites suggests an infracrustal I-type source, and regionally available Devonian-Carboniferous I-type granodiorites and tonalites satisfy the isotopic constraints. The granites classify as A-type (preferred term A-subtype) and Within-Plate Granites on standard diagrams, but the least fractionated rocks clearly indicate the I-type, Volcanic Arc Granite geochemical signatures of their inferred crustal sources.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 1992

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