Cerro Uyarani : uma janela estrutural pré-cambriana no Altiplano Boliviano : petrogênese e significado tectônico

Abstract

The pre-Andean basement consists of thirteen major paleoproterozoic terranes as well as the Arequipa-Antofalla Terrane, and among its outcrops occurs the Uyarani Granulite partially covered by Quaternary sediments, and a Pliocene ignimbrite. The Uyarani Granulite is characterized in this paper as a granulite felsic who presenting mafic enclaves of Mafic Granulite. The felsic granulite is called granulite biotite-hypersthene to felsic band

and hypersthene± hornblende granulite to mafic band and the Mafic Granulite is called hornblende- hypersthene granulite.

The structural analysis reveals the polydeformed character of these rocks which have undergone three phases of deformation F1, F2 and F3 and a brittle event marked by F3 fractures and faults. The F1 stage is related to the M1 granulite facies metamorphism acting on the Uyarani Granulite, while the F2 phase is marked by M2, a greenschist facies retro-metamorphism. Lithochemistry reveals that the granulites are originated by mixing magma, the protolith of felsic granulite has a calc-alkaline signature, varying from metaluminous to peraluminous, magnesian, however the Mafic Granulite enclaves reveal calc-alkaline magmas. Geochronological analysis yielded a crystallization age of 1736±5.1 Ma U-Pb in zircon for the felsic granulites while a metamorphic age of 1157±60 Ma (Wörner et al., 2000) indicate the involvement in a regional thermal episode associated with the evolution of the Grenvillian-Sunsás Orogeny also in the studied granulites rocks, suggesting though its relationship with mobile belts of the geochronological Sunsás Province in the SW Amazon Craton.