Meso- to Neoproterozoic terrane accretion: Insights from juvenile mafic magmatism from the Votuverava Group and Embu Complex, southern Ribeira Belt, Brazil

Abstract

Terranes of the Neoproterozoic Ribeira Belt record processes related to West Gondwana assembly. However, the evolutionary history of the belt in the preceding Rodinia supercontinent cycle and its role in the transition to West Gondwana assembly is poorly known. New geochemical and geochronological data of mafic magmatism from Meso- to early Neoproterozoic rock units (1500–900 Ma) integrated with published data provides new constraints to unravel the tectonic setting of the Ribeira Belt. Geochemical and isotopic data from the Votuverava Group and Embu Complex from the southern Ribeira Belt record three distinct periods of juvenile magmatism. Mafic rocks from the Votuverava Group define the oldest magmatism as Calymmian (1490–1475 Ma) and Ectasian (1300–1260 Ma). Both age groups display Th/Yb ratios greater than N-MORB, low Ta/Yb and Nb/La ratios, low Nb and Zr concentrations, negative Nb anomaly, whole-rock ɛNd(T) from +2.25 to +4.01, an Nd two-stage TDM model age spanning 1629–1471 Ma, and zircon εHfT mainly between +5 and +10, characteristics of juvenile mantle source arc-related magmatism. The third event occurred during early Tonian (900 Ma) and is recorded in the mafic rocks from the Embu Complex. Geochemical data indicate that these mafic rocks belong to the tholeiitic series with low LREE enrichment, negative Nb and Ta anomalies, low Nb and Zr contents and low Nb/La and Zr/Y ratios, consistent with arc-related basalts. Whole-rock Sm–Nd isotopic data yielded ɛNd(T) of +0.72 and Nd two-stage TDM model age of 1921 Ma, with zircon Hf isotopes indicating juvenile mantle sources to the mafic magmatism with ɛHfT between +4.5 and +17.2. Thus, mafic rocks from the southern Ribeira Belt record multiple periods of accretion and convergence settings associated with assembly of Rodinia and Gondwana.