The Neoarchean mafic-ultramafic São José do Jacuípe Suite in the Itabuna-Salvador-Curaçá orogen, Brazil: New U-Pb ages and geochemical data

Abstract

The São José do Jacuípe Suite (SSJJ) comprises an association of mafic and ultramafic rocks that crops out in the northern portion of the Itabuna Salvador-Curaçá Orogen (ISCO), São Francisco Craton. They are represented by small NW-SE elongated bodies comprising metamorphosed anorthosites, leucogabbros, gabbronorites, gabbros, ferrogabbros, and subordinate pyroxenites and serpentinites. The rocks are part of an orogenic belt that comprises orthogranulites and orthogneisses of the Caraíba complex, and metasedimentary rocks of the Tanque Novo-Ipirá complex, which appear to be amalgamated into a folded mélange. Petrographical analysis of the SSJJ rocks revealed relict cumulus textures in the pyroxenites. Moreover, inclusion relationships allowed the identification of two metamorphic phases; the first phase likely occurred at amphibolite facies conditions and was overprinted by granulite facies metamorphism that represents the peak metamorphic conditions recorded by the SSJJ rocks. Analytical results for major and trace elements indicate cogeneticity between the mafic rocks, and arc-related mafic cumulate field compositions. In the geotectonic environment diagrams the rocks plot in the MORB and IAT fields, indicating an origin involving melting of different sources or magma mixing. The characteristic signature of the studied rocks is represented by negative HFSE anomalies (Nb, Ti, Zr and Hf), depletion in HREE and enrichment in LILE (Ba, Rb, and Cs), indicating their derivation from metasomatic mantle in a suprasubduction setting. These data corroborate previous isotope data that point to mildly enriched mantle sources. Incompatible trace elements signatures are similar to ophiolites generated in supra-subduction zone (SSZ) environments worldwide. New U/Pb LA-ICP-MS ages indicate igneous crystallization at 2549 ± 23 Ma and 2563 ± 13 Ma for SSJJ gabbronorites, thus indicating that they postdate the other members of the magmatic arc that formed the ISCO by 20–30 Ma.