Constraints on the hercynian metamorphism in the NE lberian pyrite belt: ore textures and phyllosilicate crystallinity

摘要

In order to evaluate the efects of Hercynian metamorphism in the northeastern Iberian Pyrite Belt, a petrographic study of the different textures displayed by ore sulphides of several ore deposits (e.g., San Telmo, Cueva de la Mora, San Miguel, Aguas Tenidas Este, Concepcion), as well as a diffractometric investigation of phyllosilicates (mainly illite and chlorite) contained within metapelites in the area, have been carried out. The observed ore textures indicate low-grade metamorphic conditions below the brittle-ductile transition boundary for pyrite. Measured illite and chlorite crystallinity values, and illite b_0 data, point to a subgreenschist anchizonal metamorphism, and metamorphic conditions of T=350 deg and P approx approx 3.5+-2kb for peak metamorphism. No regional metamorphic gradient has been observed in th area and a tectonic control is suggested to account for the local variation in the deformation and recrystallization features.