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

• Published in: Earth and Environmental Science Transactions of the Royal Society of Edinburgh
• Main Authors: Weaver, S. D., Adams, C. J., Pankhurst, R. J., Gibson, I. L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1992
• Subjects: Antarctic; Byrd; Edward VII Peninsula; Marie Byrd Land; New Zealand; Antarc*; Antarctica; W. Antarctica
• Online Access: https://doi.org/10.1017/s0263593300007963; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263593300007963

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 (Ce N /Yb N = 8·4), to flat REE patterns (Ce N /Yb N = 1·1) with large negative Eu anomalies (Eu/Eu* = 0·02). Initial 87 Sr/ 86 Sr ratios are 0·7116-0·7206 and initial ε Nd 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.