AMALGAMAÇÃO DO GONDWANA OCIDENTAL NO PANAFRICANO-BRASILIANO E O PAPEL DA GEOMETRIA DO CRÁTON DO SÃO FRANCISCO NA ARQUITETURA DA FAIXA RIBEIRA

Abstract

Western Gondwana was formed at the end of the Pan-African-Brasiliano tectonic cycle, around 600 Ma, by the amalgamation of four main lithospheric plates: the West African, the Amazon and Rio de Ia Plata cratons, constituing a megaplate, the Congo - Sao Francisco plate, the Kalahari plate and the NE Brazil - Central West African plate. Pan-African-Brasiliano fold belts related to this collision are: (1) the submendional Trans-Saharan mega-belt, the Araguaia, Brasilia, Aracuai, West Congo, Ribeira, Dom Feliciano, Gariep, Malmesbury fold belts and the transverso Oubanguide-Sergipe and Damara belts elongated in a roughly E-W direction. Most of them result from a complex and multistage collision that occured in relation with the closure of a large submeridional ocean named Adamastor ocean in its southern extremity. Accurate delimitation of the different plates and unraveling of their interaction are importam to better understand orogenic processes that resulted in building the brasiliano belts. This is especially well examplified by the Brasiliano Ribeira belt. Its main structural characteristics are induced by the sudden termination of the Sao Francisco cratonic block along the 20S parallel. A model of continental collision with SW lateral escape, south of the cratonic block, is suggested. It accounts satisfactorily for the proposed kinematic reconstruction.