The 2-Ga peraluminous magmatism of the Jacobina-Contendas Mirante belts (Bahia, Brazil): Geologic and isotopic constraints on the sources

Abstract

Sabat~, P., Marinho, M.M., Vidal, Ph. and Caen-Vachette, M., 1990. The 2-Ga peraluminous magmatism of the Jacobina-Contendas Mirante belts (Bahia, Brazil): Geologic and isotopic constraints on the sources.A 500-km north-south alignment of granitic intrusions cross-cuts the central part of the Silo Francisco craton. These late-to post-tectonic granitic bodies are emplaced between two Archean blocks (Jequi~ and Gaviio blocks) and cross-cut the Contendas Mirante volcano-sedimentary sequence and the metasedimentary rocks of the Serra de Jacobina. They are two-mica or muscovite-garnet-bearing peraluminous granites.Rb-Sr systematics show that these granites were emplaced during the Transamazonian orogeny ( ~ 1.9 Ga). The high initial STSr/86Sr ratios (0.706-0.748) and the very low £'Nd(t) ( --13 to -5) indicate a crustal origin. The possible sources are: ( 1 ) the Jequi6 block; (2) the Contendas Mirante sequence; and (3) the Gaviio block, including some early Archean domes [trondhjemitie-tonalitic-granodioritic (TTG), Boa Vista type ] which were tectonically emplaced within the volcano-sedimentary sequence.The currently available Rb--Sr and Sm-Nd data are not consistent with reworking of the 3.5-Ga TTG. The combination of field and isotopic constraints preclude the Jequi~ block and the Contendas Mirante sequence and favour instead the Gaviio block medium-grade terrains as the source for the peraluminous granitic line.The available data suggest that a continent-continent collision occurred during the Transamazonian orogeny, which followed subduetion/obduction marked by volcanism (are-tholeiitic, calc-alkaline and shoshonitic) and related plutonism. 0009-2541/90/$03.50 9 40 ° ~10 o J ~ 12 ° \ ALVADOR /,,,

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

“…In all the other blocks, granitic bodies are intruded in general with peraluminous characteristics, sometimes enriched in biotite and sometimes in muscovite, with a composition close to the minimum ternary and with negative values of ε Nd (t), (-13 a -5). 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.…”

“…5); (ii) Caraiba norites and Medrado gabbros, both with ages slightly older than 2.0 Ga (Oliveira and Lafon 1995) (Tab. V) and containing important ore deposits, the first copper and the second chromium and (iii), syntectonic granites dated at 2.1 Ga (Sabaté et al 1990) (Fig. 5).…”

Isotopic Signatures of Paleoproterozoic Granitoids of the Gavião Block and Implications for the Evolution of the São Francisco Craton, Bahia, Brazil

“…2). It is important to note the variations of IRs for each sample (from very low ones up to 0.7216; Table 1) and of model ages (see above) clearly showing heterogeneity in the crustal sources of the parental magmas, in agreement with previous interpretations (Sabaté et al 1990, Pimentel & Charnley 1991.…”

“…In the northern São Francisco Craton (SFC), several granitoids associated with syn and late-tectonic phases of the Transamazonian collisional orogeny (e.g., Carnaíba, Campo Formoso, Flamengo, Riacho de Pedras, Lagoinha, Lagoa Grande, and Caetano) have been identified (Sabaté et al 1990, Santos-Pinto 1996 (Figs. 1A and B).…”

Idades Th-U-PbTde monazita e geotermobarometria de rochas metapelíticas de alto grau do sistema orogênico Itabuna-Salvador-Curaçá, BA, Brasil: um estudo em microssonda eletrônica

“…Noritos da região de Caraíba e o Gabro Medrado se colocaram há 2,0 Ga (método U-Pb em zircão, Oliveira & Lafon, 1995) e os granitos sintectônicos peraluminosos em ca. 2,0 Ga (Rb/Sr em rocha total, Sabaté et al, 1990). No complexo Ipirá, determinações em monazita com microssonda eletrônica em gnaisses aluminosos resultaram em ca.…”