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Dados Sm-Nd, Ar-Ar E Pb-Pb de corpos plutônicos no sudeste da Bahia, Brasil: implicações para o entendimento da evolução tectônica no limite orógeno Araçuaí/Cráton do São Francisco

2002; Sociedade Brasileira de Geologia; Volume: 32; Issue: 2 Linguagem: Inglês

10.5327/rbg.v32i2.972

2317-4889

Luiz César Corrêa-Gomes, Elson P. Oliveira,

earthquake and tectonic studies

The Potiragua and Itabuna-Itaju do Colonia shear zones, on the southeastern region of the Sao Francisco Craton, Bahia State, have their origin associated with the evolution of the Neoproterozoic Aracuai orogen. Alkaline plutons and dykes associated with these shear zones and their basement rocks were dated by the Sm-Nd, Ar-Ar and Pb evaporation techniques. Basement rocks yielded Pb-Pb ages between 2,089 ± 4 Ma (tonalite) and 2,079 ± 4 Ma (mesoperthite granite), and Nd model ages (T DM ) between 2,562-2,542 Ma (mesoperthite granite). The alkaline rocks, on the other hand, yielded the following results: Potiragua Syenite (Pb-Pb=732 ± 3 Ma; T DM =1,350 Ma), Potiragua felsic alkaline dyke (Pb-Pb= 676 ± 15 Ma; T DM =1,416 Ma), Itaju do Colonia tholeiite dyke (T DM =1,371 Ma), Ibicarai Syenite (Pb-Pb = 688 ± 10 Ma; T DM =1,306 Ma), Itabuna Syenite (T DM =1,416 Ma), Itabuna felsic alkaline dykes (Pb-Pb = 551 ± 36 Ma; Ar-Ar = 478 ± 26 Ma; T DM =1,157 Ma, 1,115 Ma, 1,026 Ma), Itabuna mafic alkaline dyke (Ar-Ar = 506 ± 9 Ma; T DM =986 Ma, 934 Ma). Inherited zircons from felsic alkaline rocks showed Pb evaporation ages between 2,594 Ma and 1,889 Ma, indicating interaction of the primary alkaline magma with preexisting continental crust. Some of the Nd model ages of the alkaline rocks are thus likely to be mixing ages. Our results, compared with anterior data observed in literature, also indicate that the present southeastern region of the Sao Francisco, in Bahia State, has been reworked and intruded by igneous bodies during the Palaeoproterozoic, the Meso/Neoproterozoic limit and the Neoproterozoic/Neoproterozoic-Phanerozoic limit (in response to deformation in the adjacent Aracuai orogen).