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SÍNTESE DO CONHECIMENTO SOBRE A EVOLUÇÃO GEOTECTÔNICA DAS ROCHAS METAMÓRFICAS ARQUEANAS E PALEOPROTEROZÓICAS DO EMBASAMENTO DO CRATON DO SÃO FRANCISCO NA BAHIA

1997; Sociedade Brasileira de Geologia; Volume: 27; Issue: 3 Linguagem: Inglês

10.5327/rbg.v27i3.593

2317-4889

Johildo Salomão Figueirêdo Barbosa,

earthquake and tectonic studies

Based on recent geological data, a synthesis of the geotectonic evolution of the basement rocks from the Sao Francisco Craton in Bahia state is presented. At the southwest and southeast, in the Gaviao Block, TTGs considered as the oldest rocks in Latin America (~3,4Ga) were identified intruding a substratum not clearly defined yet. In this block, within the 2,9/2,8Ga interval, a continental crust of an essentially granite/granodioritic composition has been formed. It was migmatized at the amphibolite fades and includes remnants of greenstone belt sequences (Contendas-Mirante, Umburarias, Riacho de Santana). In the Jequie Block, on the other hand, enderbitic-charnockitic multiple intrusions occurred at about 2.7/2.6Ga. They intruded older granulitic rocks with ages close to 3. IGa, probably correlated with those of the Santa Isabel Complex, the Gaviao Block, based on the field and lithogeochemical evidences. The Itabuna Mobile Belt, from the paleoproterozoic at about 2.1/2.0Ga, was established on the east side of the Jequie Block, and is made up of high grade metamorphic rocks, with a chemistry similar to rocks of archean island arcs. In the northeast, Paleoproterozoic protholits (Salvador-Curaca Mobile Belts) were formed between two archean blocks, the Mairi and the Serrinha blocks. The former includes the Mundo Novo Grenstone Belt, and the Jacobina Group and the latter, the Rio Capim and the Rio Itapicuru Greestone Belts, the last formed close to 2.2/2.1 Ga. At about 2. l/2.0Ga, a regional metamorphism was imposed at the southwest, southeast and northeast, producing granulitic blocks that, under the contemporary tectonics, now superpose belts ranging from amphibolitic to greenschists facies. This metamorphism and its related tectonic deformation are considered to be Transamazonian Cycle and were so strong that they obliterated a large part of previous tectonic cycles developed in the area.