Archean and Paleoproterozoic crust of the São Francisco Craton, Bahia, Brazil: geodynamic features

Abstract

Recent geological, geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the São Francisco Craton in Bahia. The oldest is the Gavião 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–Curaça 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 plutonic suite, and also contains strips of intercalated metasediments and ocean floor/back-arc basin gabbro and basalt. In the SSW part of the area the Jequié 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.