Linking sedimentary provenance, climate and tectonics in the Neoproterozoic Seridó Belt, Borborema Province (NE Brazil)

Abstract

The Seridó Belt, at the extreme northeast of Brazil, is one of the several Neoproterozoic mobile belts related to the Brasiliano/Pan-African Orogeny in Western Gondwana. The lithostratigraphy of the Seridó Belt comprises basal quartzites and metaconglomerates (Equador Formation) overlain by hornblende-bearing paragneisses, calc-silicate rocks and marbles (Jucurutu Formation) and biotite-schists (Seridó Formation). We investigated the sedimentary provenance of these rocks based on an integration of compiled whole-rock geochemistry, Sm-Nd isotopes, U-Pb detrital zircon ages and a new set of whole-rock trace elements analyses. Equador Formation quartzites have major and trace elements patterns that resemble cratonic sandstones, with a typical felsic provenance consistent with the isotopic composition of plutonic Archean to Paleoproterozoic basement rocks. Geochemical proxies suggest that these rocks were deposited in fresh waters under anoxic conditions and moderate to intense weathering conditions (CIA = 58–79). A shift in provenance led to an increase in intermediate-mafic sources during the deposition of the Jucurutu and Seridó formations. Trace elements from rock types in these units are nearly identical, yet they differ on the contents of some high field-strength elements (e.g., Sc, V and Ni), which are higher in the Seridó Formation than average pelites. Geochemical proxies show similar depositional environments, with brackish to marine conditions for the Jucurutu and Seridó formations under anoxic to euxinic conditions. Weathering conditions are consistently lower in the Jucurutu Formation (CIA = 58–66) in comparison with the Seridó Formation (CIA = 60–88). Compiled U-Pb data suggest maximum depositional ages of 633 ± 11 Ma and 633 ± 6 Ma for Jucurutu and Seridó formations, respectively, suggesting deposition following the ca. 645–635 Ma Marinoan glaciation. We compared the geochemistry of the Seridó Formation schists with currently exposed basement rocks and showed a strong affinity with Neoproterozoic arc-related intermediate rocks, which is in agreement with their slightly radiogenic signature (average εNd(630Ma) = –1.68). When comparing with other pelitic sequences on the western Borborema Province, most of them fit the same sources and weathering conditions of the Seridó Formation schists and Jucurutu Formation paragneisses. We propose that the Seridó Belt represents an intracontinental rift basin (Equador Formation) that was overlain by fine-grained magmatic arc-related sediments (Seridó and Jucurutu formations) during the post-Marinoan deglaciation and sea level rise. Similar pelitic deposits in western Borborema Province suggest a large marine-influenced continental depositional system that was mostly sourced from magmatic arcs of the West Gondwana Orogen.