Geological features and the Paleoproterozoic collision of four Archean crustal segments of the São Francisco Craton, Bahia, Brazil: a synthesis

Recent geological, geochronological and isotopic research has identified four important Archean crustal segments in the basement of the São Francisco Craton in the State of Bahia. The oldest Gavião Block occurs in the WSW part, 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, termed the Itabuna-Salvador-Curaçá 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 Jequié 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 Transamazonian 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 around 2.0 Ga. Pesquisas recentes, geológicas, geocronológicas e isotópicas identificaram quatro importantes segmentos crustais arqueanos no embasamento do Craton do São Francisco na Bahia. O mais antigo, Bloco do Gavião, ocorre na parte WSW, no qual têm sido identificadas rochas de composição essencialmente granítica, granodiorítica e migmatítica incluindo remanescentes de TTGs, considerados como representantes das rochas mais antigas do continente sul americano (~ 3, 4Ga) os quais estão associados a seqüências de grenstone belts arqueanos. Ao longo da costa atlântica, da parte SE passando por Salvador e seguindo em direção ao NE está exposto o segmento mais jovem, denominado de Cinturão Itabuna-Salvador-Curaçá. Este é composto essencialmente de tonalitos/ trondhjemitos incluindo faixas de metassedimentos e basaltos/gabros de fundo oceânico e/ou bacias back-arc. Na parte SE-SSW da área aflora o Bloco de Jequié sendo caracterizado por migmatitos arqueanos com inclusões de supracrustais além de intrusões multiplas charnockíticas. No NE, ocor