Evolución metamórfica de los esquistos de AP/BT de Ceán (Unidad de Malpica-Tui, NW del Macizo Ibérico)

Abstract

Metapelitic schists from the upper structural levels of the Malpica-Tui Unit contain an initial blueschist facies mineral assemblage that appears mainly preserved as micro-inclusions in garnet, albite and chloritoid porphiroblasts defining a S1 foliation. The main foliation (S2) represents an evolution of the S1 to slightly higher temperature and lower pressure, but it is still developed in blueschist facies conditions. Post-S2 deformations include restricted development of spaced C’ shear bands, tight and straight D3 folds and a later gentle subhorizontal crenulation formed in greenschists facies conditions. Garnet-phengite thermometry and GRIPS and GASP barometry calculations, using micro-inclusion compositions, indicate peak conditions around P=19-22 Kbar and T=430-500 ºC. The same calculations using the S2 fabric minerals yield approximate values of P=16-19 Kbar and T=440-515 ºC.