Geochemistry, U-Pb and Sm-Nd isotopic constraints on Rhyacian metamafic-metaultramafic plutonic rocks in the southern São Francisco paleocontinent, Mineiro belt, Brazil: petrogenesis and tectonic implications

Mafic and ultramafic rocks are crucial for understanding the Earth’s evolution, offering insights into ancient crustal formation, orogenic processes, and continental assembly. This study examines the petrogenesis and metamorphic history of the Mineiro belt, a key Paleoproterozoic accretionary system in Brazil’s southern São Francisco-Congo Paleocontinent. Using petrographic analysis, whole-rock and mineral geochemistry, and U-Pb and Sm-Nd isotopic data, we investigated the Rio Grande metagabbro, Forro metapyroxenites, and metaperidotites. Our findings reveal Rhyacian tholeiitic magmatism, with U-Pb zircon crystallization ages of 2111 ± 10 Ma and 2113 ± 14 Ma for the Rio Grande metagabbro and 2116 ± 39 Ma for the Forro metapyroxenite. These ages correlate with the fifth Paleoproterozoic mafic-ultramafic magmatism episode (2.18–2.10 Ga) in the SFCP and Columbia supercontinent formation. Isotopic signatures indicate a depleted mantle source with minor crustal contamination (εNd(t) = -0.46 to +4.10) and Neoarchean source influence (2.72–2.78 Ga TDM ages). Metamorphic evolution includes early greenschist facies hydration, followed by amphibolite facies metamorphism and a later low-grade overprint. Furthermore, we identified a Neoproterozoic anatectic event (590 Ma) that affected the Rio Grande metagabbro, constraining a period of crustal reworking associated with the Western Gondwana assembly and inward decratonisation along the southern São Francisco craton margins.