Structural and compositional evolution of Cr-Spinels and Hornblendes, Palma Group, Rio Grande do Sul, Brazil

Abstract

One amphibolite facies metamorphic event is registered in chromites and hornblendes from the Palma Group serpentinitcs and meta-andesites. Brazil's southernmost Rio Grande do Sui State. Metamorphism was apparently caused by syntectonic injection of voluminous Camhai Group meta-granitoids and not hy post-tectonic Jaguari Granite intrusion. Regional metamorphic hornblendes are in direct contact with magmatic pargasites. which indicates that it was the first metamorphic event in the area. Both hornblendes in Campestre Formation and Cr-spinels in Cerro da Cruz Formation are little zoned, an indication that only one melamorphic event was of regional extent. Recrystallization to chlorite + epidote greenschist facies parageneses is restricted to shear zones and volumetrically small.