El metamorfismo de alta presión-baja temperatura en los esquistos de Filali-Benzou (Sébtides, Marruecos) Termobarometría con la asociación cloritoide-granate-fengita

Abstract

The paleozoic schist rocks of Benzou outcrop in the core of the Beni Mzala's antiformal stack (Upper Sebtides units). In these schist rocks, we have found the association garnet (XFe=0.89-0.94), chloritoid (XMg=0.12-0.22), chlorite (XMg=0.40-0.45), biotite (XMg=0.37) and fengite (Si=3.23-3.44 a.p..u.) which grows in the KFMASH system with a ferrous tendency. The metamorphic peak has been estimated around 12 Kbar in pressure and 500°C in temperature According id the garnet (XFe=0.94) ± fengite (Si=3.44 a.p.u) association and the Chloritoid + Biotitè = Garnet + Fengite equilibrium. The secondary mineral association: chloritoid, biotite, chlorite and fengite (Si=3.1 7-3.23) indicates a pressure drop accompanied by cooling during the post-pèak path. The thermobarometriC data show that these Palaeozoic rocks have suffered a high-pressure low-temperature metamorphism in contrast with the classic estimations of P-T conditions of schist rocks belonging to Filali units (Palaeozoic in âgé; P=5-7 Kbàr y T=550-700°C). We propose that Benzou schist rocks are the lower part of the Beni Mzala unit and they could be transitional levels to the metapelite formations represented in the Filali units. Similar transitional metápélite rocks have been observed in the Alpujarride units