Archean and paleoproterozoic crust of the Sao Francisco Craton, Bahia, Brazil:: geodynamic features

Recent geological, geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the Sao Francisco Craton in Bahia. The oldest is the Gaviao block in the WSW part of the studied area, and comprises granitic, granodioritic and migmatitic continental crust including remnants of 3.4 Ga TTGs which are amongst the oldest rocks in South America, and are associated with Archean greenstone belts. The youngest segment is exposed in the Itabuna-Salvador-Curaca belt which extends from SE Bahia along the Atlantic coast to Salvador, then northwards into NE Bahia. It is mainly composed of a low-K calc-alkaline platonic suite, and also contains strips of intercalated metasediments and ocean floortback-arc basin gabbro and basalt. In the SSW part of the area the Jequie block comprises granulitic migmatites with inclusions of supracrustal rocks, intruded by many charnockite plutons. In the NE, the Serrinha block is composed of orthogneisses and migmatites which form the basement for Paleoproterozoic greenstone belts. During the Paleoproterozoic Transamazonian Cycle, these four crustal segments collided, resulting in the formation of an important mountain belt. The regional metamorphism, resulting from the crustal thickening associated with the collision, occurred at around 2.0 Ga. Major mineralizations were formed during the evolution of the four Archean blocks, and also during and after the Paleoproterozoic collision. (C) 2004 Elsevier B.V. All rights reserved.