Microprobe and in situ Sr-isotope measurements on volcanic plagioclase crystals from the silicic arc-adjacent Loicas Trough volcanic system, Argentina

In this study, we explore the geochemical characteristics of volcanic centres in the Loicas Trough including Tromen Volcano and Domuyo Volcano. The Loicas Trough is an arc-adjacent volcanic province that hosts abundant silicic lava eruptions, situated between the Andean main and back arc in the Southern Volcanic Zone, Argentina. We explore the open system processes occurring in the Loicas Trough through in situ major element and 87Sr/86Sr compositions of plagioclase crystals. The major element compositions were obtained through EMPA microprobe profile analyses on polished carbon-coated thick sections. The in situ Sr isotope compositions on the same crystals were analysed using LA-ICPMS. Plagioclase phenocrysts indicate several disequilibrium events, including recharge as seen from zonation, resorption and sieve textures and An% profiles. In situ Sr isotope measurements displayed limited intra-crystal variation significantly beyond analytical uncertainty, although in a few cases lower 87Sr/86Sr rims consistent with recharge event eruption triggers were observed.

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