Geological features and the Paleoproterozoic collision of four Archean crustal segments of the Sao Francisco Craton, Bahia, Brazil.: A synthesis

Recent geological, geochronological and isotopic research has identified four important Archean crustal segments in the basement of the Sao Francisco Craton in the State of Bahia. The oldest Gaviao 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 (similar to 3, 4Ga) and associated Archean greenstone belt sequences. The youngest segment, termed 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-are 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 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.