Geocronologia U/Pb (Shrimp), 207Pb/206Pb, Rb/Sr, Sm/Nd e K/Ar dos terrenos Granito/Greenstone do bloco do Gavião: implicações para a evolução arqueana e proterozóica do Cráton do São Francisco, Brasil

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

“…The geochemical and isotopic characteristics of these later intrusions supports the hypothesis that they were produced predominantly by crustal melting (Sabaté et al 1990). With a major concentration in the NE of Bahia, these granites exhibit, in general, Pb/Pb ages of about 2.0 Ga (Caculé, Serra da Franga, Poço Grande, Ambró- Pinto 1996, Bastos Leal 1998, Gaal et al 1987. Therefore they can be originated from the melt of hydrated rocks of the amphibolite facies, tectonically placed under rocks of the granulite facies as mentioned before.…”

“…4), during the Paleoproterozoic Transamazonian Cycle resulting in the formation of a mountain belt with a lenght approximately 600 km, N-S, and a mean width of 150 km, W-E. The traces of this collision are found not only in the structural features, but also by studying the pre-and syntectonic Paleoproterozoic rocks that are intruded into the above mentioned crustal segments, mainly in the Gavião Block (Marinho 1991, Santos Pinto 1996, Bastos Leal 1998, Mougeot 1996 Itabuna -Salvador -Curaçá Belt (Ledru et al 1997, Oliveira andLafon 1995, Barbosa andPeucat, in preparation) and Serrinha Block (Silva 1987, Oliveira et al 1999, Mello et al 2000 (Fig. 5).…”

“…The second group, with ages of 3.2-3.1 Ga. (Serra do Eixo/Mariana/Piripá Granitoids, Tab. I), had similar origin but underwent some crustal contamination (Martin et al 1991, Marinho 1991, Santos Pinto 1996, Cunha et al 1996, Bastos Leal 1998. The greenstone belts (Contendas Mirante, Umburanas, Mundo Novo) (Marinho 1991, Mascarenhas and Silva 1994, Cunha et al 1996, Bastos Leal 1998, were formed in intra-cratonic basins of the early TTG crust, initially with the formation of continental volcanics rocks with age of ∼ 3.3Ga (Contendas Acid Sub-Volcanic and Jurema Travessão Tholeiites, Tab.…”

“…Lithologies of the greenschist facies which compose the greenstone belts associ-ated to granitoid-migmatitic terrenes represent very small areas when compared to the distribution of high to medium grade. To explain the geological evolution of these older rock units of Bahia we reexamine the existing tectonostratigraphic subdivisions (ancient cores of TTGs, the Gavião Block, Contendas-Mirante Greenstone Belt, Jacobina Group, Jequié Complex, Itabuna Belt, Serrinha Core, Mairi Block, Rio Itapicuru and Capim Greenstone Belt (Barbosa and Dominguez 1996) together with most recently acquired data from Santos Pinto (1996), Bastos Leal (1998), Sato (1998), Teixeira et al (2000) and Mello et al (2000), and new radiometric and petrological evidences (Barbosa and Peucat and Barbosa et al in preparation). In this way, the new data allow us to group the disparate units listed above into four blocks of Archean age which underwent collision in the Paleoproterozoic in the period during which the Transamazonic granitoids were mainly formed.…”

Idades U-Pb (LA-ICPMS) para as suítes Caraguataí e Jussiape, Bloco Gavião, Bahia

“…Com isso, pretende-se contribuir para o entendimento da evolução tectônica do embasamento da porção nordeste do Cráton do São Francisco, que representa um dos segmentos crustais mais antigos da plataforma sulamericana, com idades isotópicas variando entre 3,5 e 2,1 Ga (Leal 1998, Cunha et al 1996. Para obtenção desses resultados foram utilizadas as técnicas de datação U-Pb por LA-ICPMS (Laser Ablation -Inductively Coupled Plasma Mass Spectrometry) e idades modelo Sm-Nd T DM por TIMS (Thermal Ionization Mass Spectrometry).…”