Paleoproterozoic greenstone-granite belts in Northern Brazil and the former Guyana Shield - West African Craton province

Abstract

The mainly meta-volcano-sedimentary Vila Nova Group and associated granites constitute separate belts, which form part of a large paleoproterozoic (mainly rhyacian) province in the Guyana Shield of which northern Brazil forms a part, and the West African Craton. In Brazil the southwestern Serra do Ipitinga and Serra Tumucumaque-Serra do Navio belts have no obvious geometrical extensions in the Guyanas or Venezuela, and may represent deposits formed at penecontemporaneous passive continental margins and ocean floor spreading centres. To the Northeast the Serra Lombarda-Tartarugalzinho and Oiapoque belts are continuations of Guianese belts. In the former the igneous rocks have geochemical characteristics of suprasubduction environments. Belts in the Guyana Shield and West African Craton have many similar features. The megaprovince evolved in a number of stages, which may have started at about 2.3 Ga, and continued with diminished activity after 2.11 Ga. Both major juvenile additions and (possibly minor) reworking of earlier crust contributed to the growth of the province. The major transcurrent deformation, responsible for the present structure of the belts, probably occurred during the later stages of evolution of the province, but metamorphism and deformation are registered even in the oldest rocks.