Evolución metamórfica de los esquistos con Grt-St-Ky del antiforme de Arinteiro (Complejo de Órdenes, noroeste del Macizo Ibérico)

Abstract

The Órdenes Series in the Arinteiro anti form are generally Grt-St-Ky schists which exhibit a regional schistosity (SJ and a metamorphic peak mineral assemblage with Qtz-Pl-Ms-Bt-Grt-Ky-Rt-llm. Some garnets show a distinctive pétrographie zoning which correlates with compositional zoning patterns. Kyanite occurs as stretched aggregates, usually surrounded by a shimmer aggregate of muscovite. Staurolite is scarce and develops allotriomorphic crystals partially replaced by garnet and kyanite. Mineral analyses were undertaken in six samples of Grt-St-Ky schists to obtain mineral chemistry and PT determinations, with special attention given to the characterization of garnet and plagioclase zoning, and avoiding later reequilibration between Fe-Mg minerals. PT conditions were calculated using the TWEEQU method with core and rim compositions of garnet and, plagioclase, and an average composition of matrix biotite. Peak metamorphic conditions can be divided into a baric and a thermal peak. The obtained PT path is interpreted to be a consequence of crustal thickening occurred in Lower Ordovician times. This evolution is clearly different from that registered in the underlying high-P and high-T units