THE ARCHEAN GRANULITE TERRAIN FROM EAST BAHIA, BRAZIL

ELSON PAIVA DE OLIVEIRA, MÁRIO IVAN CARDOSO DE LIMA, UBIRAJARA FERREIRA DO CARMO, EBERHARD WERNICK

Resumo


Granulite fades rocks belonging to the Jequié Complex crop out in a north-south trending belt more than 480 km long on the eastern portion of the state of Bahia, Brazil. They are separated into two tectonic blocks, one of Archean age named "the Jequié Block" and the other "the Itabuna Block", to the east of the first which consists of intensively reworked Archean basement rocks during the Early to Middle Proterozoic Transamazonian cycle. They are composed mostly of charnockitic to enderbitic gneisses and piriclasites, migmatized or not, with minor amounts of migmatites, khondalites, calc-silicate rocks, quartzitos, marbles, iron formations, gondites, amphibolites, anorthosites and mangeritic to syenitic gneisses. Rocks of basic to intermediate compositions predominate in the Itabuna block, whereas the acidic ones are more common in the Jequié block. The structural features observed in the field as well as on radar imagery combined with petrographic and geochronological data confirm the polycyclic nature of the Jequié Complex. Recent major and trace element analysis are presented and compared with other granulite terrains around the world. The physical conditions of the granulite metamorphism are estimated to be between 6-9 kb of pressure and 740°C - 850°C of temperature based on the mineral assemblages observed and on experimental data available in the literature.


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