The Charrua Ocean and the tonian record of Southernmost Brazil: igneous and metamorphic history of the São Gabriel Terrane

Abstract

The São Gabriel Terrain (SGT) is the only crustal segment in Southern Brazil composed of Tonian juvenile rocks, representing one of the best preserved remnant of ophiolitic complexes existing in Western Gondwana. The SGT comprises a succession of arc-related associations (metavolcano-sedimentary and orthogneisses complexes, accretionary prism association with ophiolitic complexes) and passive margin metasedimentary sussessions. The available ages range from 0.96 to 0.70 Ga with peaks at 0.9-0.82 Ga and 0.77-0.69 Ga. The main source area for the arc-related complexes is the intra-oceanic arc magmatism associated to Passinho (0.9-0.85 Ga) and São Gabriel (0.78-0.72 Ma) orogenic events. Once presenting an evolution whose age differs from both the Paleoproterozoic Rio de La Plata/Paranapanema craton and the Neoproterozoic Dom Feliciano Belt adjacent domains, the SGT is a key piece in understanding the articulation between these domains. This project based in field observations, petrography and isotope geochemistry focus on the characterization of the structure, kinematics, metamorphism and age of the ophiolites and metamorphic successions observed in the SGT. The studies proposed in this thesis aim to decipher the significance of the magmatic and tectonic events associated with the early stages of neoproterozoic orogenies in south Brazil. Thus, based on the discrimination between the Tonian terranes and the later Cryogenian-Ediacaran lithostructural units, we intent to insert this domain in the regional tectonic models. (AU)