GEOQUÍMICA DOS ORTOGNAISSES GRANULÍTICOS DO COMPLEXO JUIZ DE FORA, SEGMENTO CENTRAL DA FAIXA RIBEIRA, BRAZIL

The Juiz de Fora Complex (JFC) in the surroundings of Juiz de Fora (MG) town records a complex geological evolution, with recurring deformational and high-grade metamorphic events from the Archean to the Lower Cambrian. The JFC comprises pre-1.8 Ga. granulite facies orthogneisses, migmatites and metabasites, with subordinated amphibolite facies orthogneisses. The JFC occurs as thrust sheets within post-1.8 Ga amphibolite facies metasedimentary rocks and within orthopyroxene-bearing migmatitic paragneisses of undetermined age. Recurring tectonic events led to the general obliteration of original textures, structures and paleogeography. Field and petrographic data allow the subdivision of the orthogranulites into mafic, intermediate, and felsic granulites. Imobile and Rare Earth elements suggest that (a) the mafic granulites are tholeiitic and that each sample represents different stages of differentiation of one parental magma, (b) the intermediate and felsic granulites are calc-alkaline, and (c) no petrogenetic link seems to exist between the tholeiitic and the calc-alkaline rocks, but some evidences point to possible link among the calc-alkaline rocks.