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

Abstract

A 500-km north-south alignment of granitic intrusions cross-cuts the central part of the São Francisco craton. These late- to post-tectonic granitic bodies are emplaced between two Archean blocks (Jequié and Gavião 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 87 Sr 86 Sr ratios (0.706–0.748) and the very low ϵ Nd( t) (−13 to −5) indicate a crustal origin. possible sources are: (1) the Jequié block; (2) the Contendas Mirante sequence; and (3) the Gavião block, including some early Archean domes [trondhjemitic-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 Jequié block and the Contendas Mirante sequence and favour instead the Gavião 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 subduction/obduction marked by volcanism (arc-tholeiitic, calc-alkaline and shoshonitic) and related plutonism.