Petrogenesis of the rifted Southern Victoria land lithospher

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TitlePetrogenesis of the rifted Southern Victoria land lithospheric mantle, Antarctica, inferred from petrography, geochemistry, thermobarometry and oxybarometry of peridotite and pyroxenite xenoliths from the Mount Morning eruptive centreAbstractThe lithospheric mantle beneath West Antarctica has been characterized using petrology, wholerock and mineral major element geochemistry, whole-rock trace element chemistry and Mössbauer spectroscopy data obtained on a suite of peridotite (lherzolite and harzburgite) and pyroxenite xenoliths from the Mount Morning eruptive centre, Southern Victoria Land. The timing of pyroxenite formation in Victoria Land overlaps with subduction of the Palaeo-Pacific plate beneath the Gondwana margin and pyroxenite is likely to have formed when fluids derived from, or modified by, melting of the subducting, eclogitic, oceanic crustal plate percolated through peridotite of the lithospheric mantle. Subsequent melting of lithospheric pyroxenite veins similar to those represented in the Mount Morning xenolith suite has contributed to the enriched trace element (and isotope) signatures seen in Cenozoic volcanic rocks from Mount Morning, elsewhere in Victoria Land and Zealandia. In general, the harzburgite xenoliths reflect between 20 and 30% melt depletion. Their depleted element budgets are consistent with Archaean cratonization ages and they have mantle-normalized trace element patterns comparable with typical subcontinental lithospheric mantle. The spinel lherzolite mineral data suggest a similar amount of depletion to that recorded in the harzburgites (20-30%), whereas plagioclase lherzolite mineral data suggest <15% melt depletion. The lherzolite (spinel and plagioclase) xenolith whole-rocks have compositions indicating <20% melt depletion, consistent with Proterozoic to Phanerozoic cratonization ages, and have mantle-normalized trace element patterns comparable with typical depleted mid-ocean ridge mantle. All peridotite xenoliths have undergone a number of melt-rock reaction events. Melting took place mainly in the spinel peridotite stability field, but one plagioclase peridotite group containing high-sodium clinopyroxenes is best modelled by melting in the garnet field. Median oxygen fugacity estimates based on Mössbauer spectroscopy measurements of spinel and pyroxene for spinelfacies conditions in the rifted Antarctic lithosphere are -0·6 Δlog fO2 at Mount Morning and -1·0±0·1 (1σ) Δlog fO2 for all of Victoria Land, relative to the fayalite-magnetite-quartz buffer. These values are in good agreement with a calculated global median value of -0·9±0·1 (1σ) Δlog fO2 for mantle spinel-facies rocks from continental rift systems. © The Author 2015.AcknowledgementsWe thank Damian Walls, Brent Pooley, Andreas Audetat and Detlef KrauÃŸe for analytical support and useful discussion. Kurt Panter, Massimo Coltorti and an anonymous reviewer are thanked for constructive reviews, and John Gamble for editorial handling. A.P.M. was supported by an Antarctica New Zealand (NZ Post) Antarctic scholarship, a University of Otago award from the Department of Geology and a Marie Curie Fellowship supported by the European Commission under the Marie Curie Action for Early Stage Training of Researchers within the 6th Framework Program (contract number MEST-CT-2005--019700). Antarctica New Zealand provided fieldwork logistical support.

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1st AuthorMartin, A.AuthorMartin, A.Price, R.Cooper, A.McCammon, C.Year2014JournalJournal of PetrologyVolume56Number1DOI10.1093/petrology/egu075URLhttps://www.scopus.com/inward/recor.....e8024b9fa569cb790d3ce50d2Keywordsbarometryeclogitefugacitygeochemistryharzburgitelherzolitelithospheric structuremantle structureoxygenperidotitepetrogenesispetrographypyroxenitespinelultramafic rockxenolith, AntarcticaEast AntarcticaMount MorningVictoria Land, rank5Author KeywordsEclogiteLithospheric mantleOxygen fugacityPyroxeniteSpinel peridotite

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TypeArticleCitationMartin, A., Price, R., Cooper, A. and McCammon, C. (2014). Petrogenesis of the rifted Southern Victoria land lithospheric mantle, Antarctica, inferred from petrography, geochemistry, thermobarometry and oxybarometry of peridotite and pyroxenite xenoliths from the Mount Morning eruptive centre. Journal of Petrology, 56(1) doi:10.1093/petrology/egu075 IdentifierMartin2014bRelevancerank5