Litogeoquímica, geoquímica isotópica Sm-Nd e Sr-Sr e geocronologia U-Pb do granitoide Córrego Fundo, na Faixa Ribeira: um exemplo de granito tipo I sin-colisional

Abstract

This work aims to characterize one of the phases of granitogenesis that occur in southeastern Brazil, through the study of granitoid Córrego Fundo. This granitoid is inserted in the tectonic context of the Western Terrain of Ribeira Belt and is characterized as a syn-collisional ɣ2 and ɣ3body. For this purpose, the following methods were used: litogeochemical analyzes, isotopic geochemistry (Sm-Nd and Sr-Sr) and geochronology (U/Pb), besides geological descriptions of mapping and petrographic. Unlike the majority of orogens, the granitogenesis of the syn-collisional stage 1 (595-560 Ma) caused the contemporary generation of S, I, and hybrid granites throughout the belt (Mendes et al, 2006). The granitoid Córrego Fundo is located in the border region between the states of Minas Gerais and Rio de Janeiro and occurs as a tabular body parallel to the regional tectonic foliation, elongated in the NE-SW direction. It presents tectonic foliation more evident in the edges, becoming more homogenous and with evidences of flow foliation in the center of the body, besides xenoliths of the host rocks. After its intrusion, the granitic body records the late deformation phases described for the Ribeira Belt. The granite body is composed of hornblende biotite granites that occur in equigranular facies, and in predominantly porphyritic facies. These lithotypes have composition varying between monzodiorites and granites, are intermediate to acids and exhibit a metaluminous to a weakly peraluminous character. They belong to the calcium-alkaline series of high-K, are ferroan and would have been generated in a syn-collisional environment, although they chemically resemble more advanced I-type granites. The isotopic data of Nd and Sr indicate crustal character for this granitoid, with very negative εNd values ranging from -15.3 and -22.7, and high initial ratios of 87Sr / 86Sr ranging from 0.752 to 0.707. TDM ages suggest contribution from two different sources of paleoproterozoic age, the Andrelândia Megasequence and the Juiz de Fora Complex. The U-Pb geochronological data determine concord ages of 575 ± 10 for equigranular facies and 579 ± 10 Ma for porphyritic facies, demonstrating that they belong to the syn-collisional 1 magmatism of the Ribeira Belt.