Correlation Between Disequilibrium Features and Mineral Chemistry at the Miocene Trayén Niyeu Volcano, Somún Curá Plateau, Northern Patagonia, Argentina.

PABLO D. CORDENONS

Viña del Mar

Congreso; International Geological Congress on the Southern Hemisphere 2013; 2013

Universidad Andrés Bello, Universidad de Chile; IGeBA, Universidad de Buenos Aires; Universitá di Urbino. Italy; Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Trieste. Italy.

ABSTRACT The Miocene Trayén Niyeu volcano (TNV) is the largest post-plateau volcanic building at the westernmost ranges of the mainly Oligocene Somún Curá volcanic shield. The TNV is formed by a large orthopyroxene-bearing basandesitic lava field of fissural characteristics, that later on develops a central strombolian dacitic-pyroclastic edifice. Most of TNV?s lavas reveal intense disequilibrium textures and micro-enclaves, that increase towards the top of the sequence. Three interacting paragenesis were interpreted from detailed petrography and mineral semi-quantitative chemistry, that cannot be ascribed to a single fractional crystallization trend: a) A basic paragenesis, with ~En75, chromium-rich orthopyroxene and ~An55 plagioclase phenocrysts; b) A hybrid magma paragenesis, involving ~Ab75 plagioclase, biotite, amphibole and apatite phenocrysts; and c) A highly differentiated paragenesis, composed of sanidine, biotite and quartz phenocrysts. These three paragenetic assemblages interact at different levels, producing a wide range of disequilibrium textures and geochemical scatter. Trayén Niyeu?s effusive style may be a key for the understanding of subduction-related geochemical signals at the Somún Curá magmatic event.