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Plumbing system processes unravelled through phenocryst texture, chemistry and in-situ Sr isotopes - The Pleiades Volcanic Field (Antarctica)

Alice Tomassini 1-2, Irene Rocchi1, Matteo Masotta1-3, Maurizio Petrelli4, Mónica Ágreda-López4, Teresa Ubide5, Sergio Rocchi1-3

  • Affiliations: 1 Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italia; 2 Department of Environmental Sciences, Informatics and Statistics, Università \"Ca\' Foscari\" di Venezia, Venezia, Italia; ^3 ^Center for Instrument Sharing CISUP, Università di Pisa, Pisa, Italia; ^4 ^Dipartimento di Fisica e Geologia, Università di Perugia, Perugia, Italia. ^5 ^School of Earth and Environmental Sciences, The University of Queensland; Brisbane, Australia. 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 202

  • Programme No: 1.9.9

  • Theme 1 > Session 9

Abstract

The Pleiades Volcanic Field (PVF), in northern Victoria Land, Antarctica, is made up of a dozen monogenetic scoria cones and two domes, with ages ranging from ca. 800 ka to present. Despite the monogenetic aspect of the edifices, the volcanic products are compositionally diverse, defining a complete mildly Na-alkaline evolutionary trend. This makes the PVF a distinctive volcanic field, whose plumbing system has likely evolved under special conditions. To unravel the architecture of the PVF feeding system, we characterized the chemistry, texture and P-T conditions of crystallisation of the crystal cargo of a set of lavas, sampled in the framework of the Italy's National Antarctic Research Program - PNRA. Moreover, we performed in-situ Sr isotopes determinations on plagioclase crystals and groundmass with laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS). Plagioclase phenocrysts display a wide range of textures (dusty mantles, coarse sieve textures, rounded cores), coupled with zonings in major (e.g. Ca-Na), trace elements (e.g. Ba) and Sr ratio (ranging in 0.7036-0.7043).  Results on plagioclase suggest efficient recycling of crystals between magmas differing in evolution degree and radiogenic isotope signatures, as well as mixing with a low 87Sr/86Sr basaltic magma in the most mafic terms of the association. The complexity of pre-eruptive processes suggests a prolonged stall of the magma at crustal depths (1.2-0.1 GPa), with a main storage zone at around 0.3 GPa, probably due to an incapability of eruption. We suggest that a variable ice load could have played a role in modulating this long-lived and vertically extended subvolcanic system.