Rhyacian-Orosirian isotopic records from the basement of the Araçuaí-Ribeira orogenic system (SE Brazil): Links in the Congo-São Francisco palaeocontinent

Abstract

Assembled during the Rhyacian-Orosirian boundary, the Congo-São Francisco palaeocontinent remained linked by a continental bridge from ca. 2 Ga to the Atlantic Ocean opening in the Cretaceous. To the south of that bridge, precursor basins and orogenic outcomes encompassed by the Neoproterozoic-Cambrian Araçuaí-Ribeira orogenic system (AROS) and its African counterparts, developed. The AROS discloses reworked basement units, like the Juiz de Fora, Pocrane and Quirino complexes, which are key units to retrieve the Palaeoproterozoic history of the Congo-São Francisco palaeocontinent. This paper presents new U-Pb ages, and the first Lu-Hf in zircon signatures from those complexes. All magmatic zircon grains show Rhyacian and Orosirian ages, ranging from c. 2250 Ma to c. 1850 Ma. The best Concordia ages range from 2184 ± 9 Ma to 2080 ± 19 Ma. Hf in zircon and whole-rock Sm-Nd data disclose mantle-related signatures for both, the Pocrane and Juiz de Fora complexes, suggesting igneous protoliths with no or very few involvement of continental crust, similarly to juvenile magmatic arcs. Conversely, Hf in zircon data for the Quirino complex show an evolved signature compatible with a magmatic arc developed on a continental older crust with Archaean components. Together with a thorough compilation on Rhyacian-Orosirian orogenic systems (ROOS), our data allow us to envisage links within the Congo-São Francisco palaeocontinent, comprising orogens characterised by mostly evolved isotopic signatures and zircon inheritance. They are grouped into the: (i) W-ROOS, including the Mantiqueira complex, the west segment of the Eastern Bahia belt, intrusions in the south Gavião and Porteirinha blocks, and parts of the Mineiro belt; and (ii) E-ROOS, comprising the Quirino complex, basement rocks of the Cabo Frio tectonic domain, the coastal Eastern Bahia belt, and, in Africa, Eburnean and Kimezian complexes, as well as the western Angola shield. Assembled between the W-ROOS and E-ROOS, an orogenic system with prominent juvenile to moderately juvenile isotopic signature (JU-ROOS) includes the Juiz de Fora and Pocrane complexes, and the Buerarema complex at the central segment of the Eastern Bahia belt.