Boron- and phosphate-rich rocks in the Larsemann Hills, Prydz Bay, East Antarctica: tectonic implications
Edward S. Grew, Christopher J. Carson, Andrew G. Christy, Steven D. Boger, 2013. "Boron- and phosphate-rich rocks in the Larsemann Hills, Prydz Bay, East Antarctica: tectonic implications", Antarctica and Supercontinent Evolution, S. L. Harley, I. C. W. Fitzsimons, Y. Zhao
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Granulite-facies paragneisses enriched in boron and phosphorus are exposed over c. 15×5 km2 in the Larsemann Hills, Antarctica. The most widespread are biotite gneisses containing centimetre-sized prismatine crystals, but tourmaline metaquartzite and borosilicate gneisses are richest in B (676–19 700 µg/g or 0.22–6.34 wt%; B2O3). Chondrite-normalized rare-earth element (REE) patterns give two groups: (1) LaN>150, Eu*/Eu<0.4, which comprises most apatite-bearing metaquartzite and metapelite, tourmaline metaquartzite, and Fe-rich rocks (up to 2.3 wt%; P2O5); (2) LaN<150, Eu*/Eu > 0.4, which comprises most borosilicate and sodic leucogneisses (2.5–7.4wt%; Na2O). Enrichment in boron and phosphorus is attributed to premetamorphic hydrothermal alteration, either in a rifted, most likely marine basin or in a mud volcanic system located inboard of a c. 1000 Ma continental arc that was active along the leading edge of the Indo-Antarctic craton. This margin developed before collision with the Australo-Antarctic craton (c. 530 Ma) merged these rocks into Gondwana and sutured them into their present position in Antarctica. Rocks lithologically similar to those in the Larsemann Hills include prismatine-bearing granulites in the Windmill Islands, Wilkes Land, and tourmaline–quartz rocks, sodic gneisses and apatitic iron formation in the Willyama Supergroup, Broken Hill, Australia.
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Antarctica and Supercontinent Evolution
Antarctica preserves a rock record that spans three and a half billion years of history and has a remarkable story to tell about the evolution of our Earth, from the hottest crustal rocks yet found in an orogenic system, to the assembly and breakup of Gondwana in the Phanerozoic. This volume highlights our improved understanding of the tectonic events that have shaped Antarctica and how these potentially relate to supercontinent assembly and fragmentation. The internal constitution of the East Antarctic Shield is assessed using information available from the basement geology and from detritus preserved as Mesozoic sediments in the Trans Antarctic Mountains. Accretionary orogenesis along the proto-Pacific margin of Antarctica is examined and the volumes of intracrustal melting compared with juvenile magma additions in these complex orogenic systems assessed. This volume demonstrates the diversity of approaches required to elucidate and understand crustal evolution and evaluate the supercontinent concept.