Petrogenesis of Mafic-Ultramafic Intrusions in the Southern Goiás Magmatic Arc, Central Brazil

Abstract

The Americano do Brasil and Mangabal Complexes belong to a cluster of Neoproterozoic mafic-ultramafic intrusions in the southern Goiás Magmatic Arc in Brazil that lies within the Brasília Belt, a complex, long-lived Neoproterozoic Orogen that formed during the amalgamation of the São Francisco/Congo, Amazonian, and Paranapanema Cratons in western Gondwana. Although deformed and partially recrystallized by a regional metamorphic overprint, the rocks of both complexes still preserve igneous textures. The rocks in both complexes show cumulate textures that range from adcumulate to orthocumulate. Petrography, geochemistry, geochronology, and petrological modeling were carried out to constrain the petrogenesis of the complexes.Modeling indicates that the parental magma for the Americano do Brasil Complex had an OIB-like Fe-rich picrite composition, while the parental magma of the Mangabal Complex could have been a tholeiitic basalt. Considering the temporal and spatial correlations, decompression melting of upwelling asthenosphere triggered by rollback subduction and/or influence of a mantle plume are plausible mechanisms to explain the petrogenesis of these mafic-ultramafic intrusions in the vicinities of the eastern Arenópolis arc and westernmost Anápolis-Itauçu belt. The complexes have experienced a protracted metamorphic evolution with peaks indicating amphibolite facies. The rock from both complexes shows late-stage alteration associated with metasomatism by CO2-Ca-S-rich fluids.