U-Pb in-situ SIMS baddeleyite and zircon dates and thermodynamic modeling of the Mangabal Complex: Indications of asthenospheric mantle influence in the formation of layered intrusions of the Brasília orogen

Abstract

The Mangabal Complex lies within the Brasília Belt, a long-lived Neoproterozoic orogen formed during the amalgamation of the São Francisco/Congo, Amazonian, and Paranapanema Cratons in western Gondwana. The complex comprises two sequences of mafic and ultramafic cumulates, separated by less than 3 km. Despite having undergone variable degrees of deformation and metamorphism, the two sequences exhibit locally preserved pristine relict igneous minerals and textures. The origin and parental magma for the complex remain poorly constrained. We present petrography, whole-rock lithogeochemistry, mineral chemistry and U-Pb in-situ SIMS data from micro-baddeleyite and zircon from Mangabal Complex rocks collected from drill holes. We show that a simple thermodynamic model of batch crystallization using a tholeiitic basalt as parental magma in the upper crust closely matches the studied rocks and agrees with a broadly comagmatic origin for the two sequences. Baddeleyite inferred to represent a primary igneous phase of the complex gives a minimum age of 653 ± 31 Ma, suggesting that the Mangabal Complex, hosted in the Arenópolis-Arc segment, could be coeval with the Damolândia and Taquaral intrusions, hosted in the high-grade Anápolis-Itauçu Complex. Considering the temporal and spatial correlations, we propose that decompression melting of upwelling asthenosphere triggered by rollback subduction and/or the influence of a mantle plume is required to explain the petrogenesis of the mafic–ultramafic intrusions in the eastern Arenópolis Arc and westernmost Anápolis-Itauçu Complex.