Abstract
The assembly of Western Gondwana, during the Neoproterozoic, involved the Sao Francisco/West Congo Craton and its passive margins. The Ribeira Belt lies along the Brazilian Atlantic Coast and is one of the products of the supercontinent amalgamation. Collisional processes were preceded by subduction, recorded by the Rio Negro Complex orthogneisses at the Ribeira Belt. Its plutonites represent a gabbrodiorite- tonalite-throndhjemite plutonic series that evolved from 637 Ma (U-Pb zircon age of the tonalite gneiss) to nearly 600 Ma, at the beginning of the collisional event. Field, petrographic, litogeochemical, and isotopic characteristics of the Rio Negro Complex point to magmatism at a very mature oceanic arc or an immature continental crust as seen along attenuated passive margins. In the latter hypothesis, the margin could be related to a microplate or to the Congo/Angola Craton.
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