Extrusion of high-grade metamorphic and anatectic rocks during inclined transpression in the central Brasília Orogen, Western Gondwana

Abstract

Ancient and modern orogens are related to transpressional tectonics due to the Earth's spherical surface, often recording synchronous deformation, metamorphism, and anatexis. In the western Gondwana supercontinent, such relations are found in the Brasília Orogen, which formed from the collision between the Paranapanema, São Francisco-Congo, and Amazonian paleoplates during the Neoproterozoic Brasiliano/Pan-African Cycle. This study aims to investigate the deformational, metamorphic, and anatectic processes active in the central Brasília Orogen through field-based geological mapping and structural analysis, petrography, and U-Pb geochronology in zircon. The data show that the internal zone of the central Brasília Orogen underwent crustal shortening in the northeast-southwest direction, synchronous with lateral escape tectonics toward the southeast, suggesting an inclined transpressional context involving strain partitioning and the extrusion of deep-to-middle crustal rocks. The structural evolution was coeval with upper amphibolite to granulite facies metamorphism and anatexis, suggesting spatial and temporal relationships between structural fabrics, metamorphic and anatectic products. In this scenario, structures acted as primary controls of melt migration and granite emplacement, just as melt weakened the crust and facilitated structure nucleation. The Tonian (ca. 0.88 and 0.80 Ga) mafic protolith of the migmatitic orthogneiss and its leucosomes together with the migmatitic paragneiss and syntectonic granites confined the feedback loop between active ductile deformation, metamorphism and anatexis to the Cryogenian and Ediacaran periods (ca. 0.65 to 0.62 Ga), broadly constraining the interval of expressive crustal flow in the Brasilia Orogen.