The 2.58 Ga São José do Jacuipe gabbro-anorthosite stratiform complex, Itabuna-Salvador-Curaçá Orogen, São Francisco Craton, Brazil: Root of the Neoarchaean Caraiba continental arc?

Abstract

Mafic-ultramafic complexes are common in ancient orogenic belts and can represent arc roots, obducted ophiolite remnants, continental intrusions, subducted oceanic plateaux or lithospheric mantle fragments. The Archaean-Palaeoproterozoic Itabuna-Salvador-Curaçá̧ Orogen hosts several mafic-ultramafic complexes, whose petrogenetic understanding is difficult owing to the high-grade metamorphism and deformation. One of these complexes is the 2583.7 ± 7.7 Ma São José do Jacuípe Gabbro-Anorthosite Complex, composed of massive to stratiform, deformed and metamorphosed anorthosites, leucogabbros, and gabbros with minor pyroxenites. Field relationships of the mafic-ultramafic rocks combined with calcic-pyroxene chemistry, negative Nb anomalies in mantle-normalised diagrams, and dominantly positive εNd(t) values suggest similarities with arc mafic magmatism. The gabbro-anorthosite complex matches the ages of arc orthogneisses (2574 ± 6 Ma) and norite-hypersthenite complex (2580 ± 10 Ma) of the Caraiba Complex and is thus interpreted as a fragment of the root of the Neoarchaean Caraíba magmatic arc within the Itabuna-Salvador-Curaçá Orogen.