Tectonic Evolution of Two Contrasting Schist Belts in Southernmost Brazil: A Plate Tectonic Model for the Brasiliano Orogeny

Two Brasiliano schist belts (Porongos belt and Sao Gabriel block) of contrasting geotectonic setting exhibiting a distinct structural evolution are exposed in the southern Brazilian shield east of the Rio de la Plata craton. Trace-element and isotope data (Sm-Nd, Rb-Sr) demonstrate that the Sao Gabriel block and Porongos belt represent two distinct tectonostratigraphic blocks, with the former consisting of Neoproterozoic juvenile rocks, and the latter being characterized by intense reworking of old continental crust. The Sao Gabriel block in the west consists of Neoproterozoic relics of two Brasiliano magmatic arcs, an intra-oceanic arc, and a younger continental arc or active continental margin. The Porongos belt located on the Encantadas block, in contrast, formed in a passive-margin setting on thinned continental crust in an extensional or transtensional regime. Basin formation was accompanied by volcanism due to partial melting of the stretched continental crust. Comparison of the structural evolution...