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Neoproterozoic oceanic remnants in eastern Brazil: Further evidence and refutation of an exclusively ensialic evolution for the Araçuaí–West Congo orogen

¹ Universidade Federal de Minas Gerais, Instituto de Geociências, Campus Pampulha, Belo Horizonte 31270-901, MG, Brazil
² Université Blaise-Pascal, 5 rue Kessler, Clermont-Ferrand 63038, France
³ Universidade de Brasília, IGC, Brasølia 70910-900, DF, Brazil
⁴ Universidade de São Paulo, IG, São Paulo 05422-970, SP, Brazil

The Araçuaí (eastern Brazil) and West Congo (southwestern Africa) belts are counterparts of the same Neoproterozoic orogen located between the São Francisco and Congo cratons. The Macaúbas Group represents a major passive margin sequence and is a key unit for interpreting the evolution of that orogen. The Salinas Formation is the distal rock assemblage of the Macaúbas Group and consists of a deep-sea sand-mud sequence, and a volcanic-sedimentary unit called the Ribeirão da Folha facies. The latter includes metamorphosed volcanic-exhalative sediments associated with ocean-floor basalts (amphibolites). The magmatic protoliths of these amphibolites crystallized at about 816 ± 72 Ma (Sm-Nd whole-rock isochron, _Nd(t) =+3.8 ± 0.2). Regional metamorphism reached the amphibolite facies at about 630 Ma (Rb-Sr whole-rock isochron), when slabs of ultramafic rocks were tectonically emplaced over the Ribeirão da Folha facies. We consider this volcanic-sedimentary facies and the coeval slabs of ultramafic rocks to be remnants of a branch of the Adamastor-Brazilide ocean. The extensive occurrence of syntectonic to late tectonic calc-alkalic granitoids along the internal domain of the Araçuaí belt implies that a reasonably large amount of ocean crust was consumed, via an east-dipping subduction zone, during formation of the Araçuaí–West Congo orogen.

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