Metamorfismo de alta-P en las rocas volcánicas submarinas de Espasante (II)Condiciones P-T y evolución reaccional

Abstract

The studied tectonic block of submarine metavolcanic rocks in the Somozas Mélange records a high- P metamorphic event developed during subduction. This metamorphic event is only clearly recorded in the hyaloclastitic matrix of the pillow-breccias. It is suggested that the first hydrothermal metamorphism affecting the hyaloclastic rocks, that strongly modified its chemical composition, favored the development of high-P mineral phases during subduction. Pseudosection modeling of the metahyaloclastites has allowed establishing the P-T conditions of the metamorphic peak mineral assemblage (muscovite+paragonite+garnet+chlorite+kyanite+hematite+epidote+quartz+rutile). Several pseudosections calculated in the KNCFMnMASHTO system indicate P-T peak conditions of 17.5-18 kbar and ca. 550ºC. Margarite appears as a retrograde mineral formed at pressure conditions below 11 kbar. The P-T path evolution shows a drastic exhumation of the metavolcanic block developed after a subduction event. The exhumation was driven by return flow in the low-viscosity subduction channel in which the mélange developed.