INVESTIGADORES
BAEZ Walter Ariel
congresos y reuniones científicas
Título:
Genesis and Eruptive Dynamics of the Garnet-Bearing Rhyolites from the Ramadas Volcanic Centre (Altiplano-Puna Plateau, Central Andes, Argentina)
Autor/es:
DE ASTIS G.; BAEZ WALTER; BARDELLI LORENZO; BECCHIO RAÚL; GIORDANO GUIDO; LUCCI FEDERICO; ROSSETTI F.; JOSÉ VIRAMONTE
Reunión:
Congreso; AGU Fall Meeting 2015; 2015
Resumen:
We present a new set of data on the volcanic products erupted by the Ramadas Volcanic Center (RVC), obtained through further 􀏐ield studies ? which follow the Tait et al. (2009) paper - and new petro-textural, mineralogical and petrological investigations. The RVC is a small monogenetic calderic depression, now largelyobliterated, almost coeval with the Late Miocene outbreak of highly explosive silicic activity occurred in the Altiplano-Puna plateau. The Ramadas volcanic activity generated a quite complex suite of garnet-bearing pyroclastic products: a coarse lithic-rich lag breccia as eruption opening, followed by plinian fall layers that in proximal-intermediateoutcrops alternated with PDC deposits. Finally, during the waning stage(s) of the RVC activity, small volume phreatomagmatic deposits (forming a tuff-ring) and a lava coulée, were emplaced. Unusually, the dominant pyroclasts in the tuff-ring sequence are non-vesiculated fragments of peraluminous (rhyolitic) perlite. It?s even more interesting thatvolcanological data together with textural and compositional features of typical tube pumices reveal the occurrence of a volatiles-rich, high-energy eruption related to an almost aphyric rhyolitic magma, with only unzoned garnet as micro-phenocrysts. Although the garnets of post-magmatic origin (e.g. the fumarolic ones) are not so rare in lavas, thoseof magmatic origin are uncommon and can crystallize only under restricted P-T conditions. The RVC rhyolites result to be atypical even for their geochemical features if compared with those outcropping in the same region. Therefore, we decided to study their genesis either through SEM observations (relationships between garnets and rhyolitic melt)and microprobe analysis on mineral phases and glass shards, with the aim to to infer the (T, P) conditions under which the garnets had originated and the processes occurred to generate such a rhyolitic magma in a probably shallow crustal reservoir (anatexis?). Finally, the ongoing research is reported.