GEOCRONOLOGIA U-Pb E Lu-Hf EM ORTOGNAISSES DA REGIÃO DE ESPERA FELIZ (MG): CONTRIBUIÇÃO A EVOLUÇÃO CRUSTAL DO EMBASAMENTO RIACIANO NO LIMITE DOS ORÓGENOS RIBEIRA E ARAÇUAÍ

U-Pb and Lu-Hf geochronology of orthogneisses from Espera Feliz region (MG): contribution to the Rhyacian evolution of the basement at the limit of the Ribeira and Araçuai Orogens

Abstract

 The Araçuaí Orogen was developed during the Brasiliano Cycle when collisional events deformed the basement represented by migmatite orthogneisses. Petrographic studies in Espera Feliz region indicate orthogneiss and paragneiss granitoids and granulites. The U-Pb and Lu-Hf analysis in zircon grains by LA-ICP-MS, allowed to obtain crystallization and metamorphic ages and informations on sources of analysed rocks. The zircons have rounded and / or elongated morphology, being possible the identification of inherited nuclei and overgrowth in the grains through the images made in the SEM. U-Pb geochronological analyzes have protolite ages varying from 2200 a 2075 Ma, (ε_Hf values from -21,8 e -8,9 and T_DM from 2,83 a 2,06 Ga), Neoproterozoic granites crystallization ages from 630 to 597 Ma and metamorphism ages from 602 Ma to 582 Ma (ε_Hf values from -14,6 and -6,7 and T_DM from 2,22 to 1,78 Ga). These results allow suggesting the formation of the Paleoproterozoic basement originated in the environment of magmatic arc (2201-1996 Ma). These rocks were intruded by neoproterozoic magmatism (626-622 Ma). The third event identified in the U-Pb ages of the rocks studied is characterized by metamorphism and crustal melting (602-582 Ma) during the collision and amalgamation of Gondwana supecontinent.