Evolução metamórfica do terreno oriental da Faixa Ribeira entre Italva e Bom Jesus do Itabapoana, noroeste do RJ

Abstract

The region between Bom Jesus de Itabapoana and Italva consists of a high-grade metamorphic terrane situated within the so-called Oriental Terrane of the Central Sector of the Ribeira Belt. This belt, of neoproterozóic-cambrian age, was formed during the Brasiliano Orogeny, in the south / southeast margin of the São Francisco Craton. The present work was developed on the basis of preexisting geological maps and collection of samples along two structural sections of the study area. The aim of this work is the investigation of the metamorphism of the Cambuci, Costeiro and Italva Domains of the Oriental Terrane. This investigation was based on the acquisition and interpretation of chemical analyses of mineral phases from metapelites and metabasites of the previously quoted domains. The identification of mineral parageneses, the discrimination of different metamorphic equilibriums and the determination of absolute values of pressure and temperature (geothermobarometry) for each one of the study tectonic domains were the basic tools used for the characterization of the metamorphic evolution of the area. The obtained data indicated different conditions and metamorphic evolutions, including different crustal levels, for the different tectonic domains of the Oriental Terrane. The rocks of the Cambuci Domain register two different thermal events, both under high temperature and medium pressure conditions. The first event, not inequivocaly metamorphic, was developed under lower pressures than the second one. The rocks of the Costeiro Domain record metamorphic peak under conditions of medium pressure granulite facies. The obtained pressure and temperature values were the highest among the three studied domains. The rocks of the Italva Domain yield temperature values of the transition zone between upper anfibolite and granulite facies conditions. Low to medium pressure values were obtained for this domain.