Colagem paleoproterozóica de placas arqueanas do cráton do São Francisco na Bahia

Abstract

Recent petrological, geochronological and isotopic researches has identified four important Archean crustal segments in the Sao Francisco Craton, SFC, in the state of Bahia. The oldest Gaviao Block occurs in the WSW part of the SFC is composed essentially of granitic, granodioritic and migmatitic rocks. It includes remnants of TTG suites, considered to represent the oldest rocks in the South American continent (~3,4Ga) and associated Archean greenstone belt sequences. The youngest segment, named the Itabuna-Salvador-Curaca Belt is exposed along the Atlantic Coast, from the SE part of Bahia up to Salvador and then along a NE trend. It is mainly composed of tonalite/trondhjemites, but also includes stripes of intercalated metasediments and ocean-floor/back-arc gabbros and basalts. The Jequie Block, the third segment, is exposed in the SE-SSW area, being characterized by Archean granulitic migmatites with supracrustal inclusions and several charnockitic intrusions. The Serrinha Block (fourth segment) occurs to the NE, composed of orthogneisses and migmatites, which represent the basement of Paleoproterozoic greenstone belts sequences. During the Paleoproterozoic Orogeny, these four crustal segments collided, resulting in the formation of an important mountain belt. Geochronological constrains indicate that the regional metamorphism resulting from crustal thickening associated with the collision process took place c.a. 2.0 Ga.