Geochronological constraints of high-grade metasedimentary rocks of the Italva and Costeiro basins: Reconstructing the Outer Magmatic Arc System of the ribeira belt, SE Brazil

Abstract

U-Pb provenance studies of the magmatic arc-related basins of the Ribeira Orogen are essential to unravel the depositional history and the paleogeography prior to the diachronic collision that has resulted in Neoproterozoic to Cambrian Western Gondwana assembly. This work brings new geology and LA-ICPMS data from metasedimentary units and felsic to mafic magmatic rocks that compose the Outer Magmatic Arc System (OMAS) in the Ribeira segment of the Araçuaí-Ribeira Orogenic system (AROS), contributing to unravel the construction of the West-Gondwana supercontinent. The OMAS evolution started in Tonian time (860–790 Ma) as the juvenile intra-oceanic Serra da Prata arc and evolved into the immature continental Rio Negro arc during the Cryogenian-Ediacaran times (650–620 Ma). The long-term subduction revealed the coeval stages development of arc-related basins. In the first Tonian stage, basin development is associated with the Italva group, divided into two sequences representing both fore and back-arc settings. The forearc sequence (Euclidelândia unit) comprises meta-psammitic sedimentary rocks with a single provenance source from the SP arc (peaks at 812 Ma and 828 Ma). The back-arc sequence (São Joaquim unit) consists of marbles with MORB-like interlayered amphibolites (ca. 831 Ma) bracketing the maximum age of carbonatic platform deposition. On the other hand, the younger Cryogenian to Early Ediacaran Costeiro back-arc basin is represented by three units of the São Fidélis group. The proximal Macuco unit, comprising meta psammitic rocks with marble, yielded a bimodal provenance distribution (852–815 Ma; 643–634 Ma), which reflects only the SP and RN magmatic arcs sources. The pelitic distal Upper and Lower units point out multimodal sources, coming from the SP-RN arc-rocks (ca 950–734 Ma; ca. 693–621 Ma) and Archean to Mesoproterozoic sources (ca. 3.12–3.0 Ga; 2.98–2.49 Ga; 2.29–1.50 Ga; 1.49–1.01 Ga), derived from ancient cratonic blocks located eastern wards, in African side. All units of the OMAS recorded two metamorphic episodes, with the oldest M1 (ca. 600–590 Ma) related to the collision of the OMAS against the Inner Magmatic Arc System (IMAS) and the younger M2 (ca. 545–533 Ma) that resulted from the final docking of the Cabo Frio terrane (Angola block) and finally closed the OMAS back-arc basin. Data obtained reinforces the long-term E-verging subduction that built the OMAS.