Foreland deformation of Brasiliano orogens at the eastern and western margins of the São Francisco Craton: K-Ar illite dating of the Araçuaí and Brasília fold-and-thrust belts Foreland deformation of Brasiliano orogens

The São Francisco Craton played a central role in the evolution of the Brasiliano Orogeny, with significant deformation along its eastern and western margins forming the Araçuaí and Brasília fold-and-thrust belts. This study investigates the timing and conditions of deformation in the upper crust of these belts using K-Ar illite dating and X-ray diffraction analysis from sedimentary covers in four regions. Samples were collected from Mesoproterozoic (Espinhaço Supergroup and Paranoá Group) and Ediacaran to Cambrian (Bambuí Group) units, in the western São Francisco Craton border (Unaí area, Brasília Belt) and eastern São Francisco Craton border (Araçuaí Belt). Results show that inherited detrital components significantly influence the isotopic system in the Unaí area, with deformation under lower temperatures (anchizonal conditions, ca. 250-270°C), and yielded older, likely mixed, Ediacaran ages that establish a maximum limit age for deformation of ca. 615–570 Ma. In contrast, K-Ar ages from the eastern São Francisco Craton margin range from ca. 510 to 455 Ma establishing a minimum limit age for cooling in epizonal conditions (ca. 350-250°C). The development of oppositely-verging, thin-skinned thrust systems is explained by a Coulomb wedge model, driven by tectonic compression from the Brasiliano Orogeny and gravitational forces from adjacent orogenic mountain building.