CARACTERIZAÇÃO PETROGRÁFICA E METAMÓRFICA DOS GRANULITOS DO ARQUEANO/PROTEROZÓICO INFERIOR DA REGIÃO DE ITABUNA - BAHIA

Abstract

PETROGRAPHIC AND METAMORPHIC CHARACTERIZATION OF THE ARCHEAN/ LATE-PROTEROZOIC GRANULITES OF THE REGION OF ITABUNA-B AMI A. The Archean/Lower Proterozoic high-grade rocks ofthe Itabunaregion in southern Bahia were separated into five assemblages. The first one was named Ilhéus Complex, being formedby intercalationsofbasic granulites with hornblende and felsic granulites with plagioclase. The second, São José Complex, is composed of intermediate to basic granulites with intercalations of garnet bearing basic granulites. The third, Ibicarai r BueTarema Complex is formed essentially of intermediate granulites and a fourth assemblage that comprises the Água Sumida (metamonzonites), Rio Paraíso (meta-syenites)and São Geraldo granitoids (this latter one of granitic composition). All the rocks ofthe former four assemblages are ofthe granulite facies of metamorphisrn. The fifth and last assemblage was named Rio Japu, being formed mostly of biotite and hornblende gneisses re-adjusted to the amphibolite facies conditions. Besides the amphibolite and granulite progressive facies the paragenetic and textural studies ofthe metamorphic reactions and mineral chemistry allowed to recognize the granulite, amphibolite and greenschist regressive facies in the area. The temperatures and pressure values for the maximum metamorphism were estimated in 6 kbar and 850°C. The geotectonic model forthe area is in agreement with the one interpreted for a northern area. In that place is taken into account the existence of a subduction zone closer to the Atlantic coastal zone and, an arc or a series of island arcs as one moves inboard the continent.