Tracing mantellic vs. crustal sources of clastic sediments in continental rifts using geochemical and Sm[sbnd]Nd and Sr isotope compositions: Insights from paleogene alluvial deposits of the Resende Basin, SE-Brazil

Abstract

This work presents combined whole-rock element and SmNd and Sr isotopes of the Eocene syn-rift I alluvial sediments of the Resende Basin (SE-Brazil), aiming the assessment of sedimentary provenance. Geochemical compositions are used to evaluate the potential effects of hydrodynamic sorting and weathering in the SmNd and Sr isotopic compositions. Mudstone, sandstone, and conglomerate samples were collected for analysis. Chemical data indicate that the major element composition of the Resende Basin sediments is compromised by present-day weathering conditions and cannot be used for source areas weathering interpretations. Similar trace and rare earth elements composition in sandstones and mudstones imply poorly mixed sediments and provenance is associated with felsic and intermediated igneous sources with a subordinate mafic component. Mudstones are enriched in elements typically associated with heavy minerals (Ti, Zr, Hf, and Y). Weathering and mineral sorting affect mainly the major and trace element compositions of the Resende Basin sediments, while most of the isotopic composition's variations are due to differences in provenance caused by different source areas and/or degrees of source mix. Based on its conspicuous contrasting isotopic signature, the Cretaceous alkaline igneous source component can be tracked in the Resende Basin sedimentary record. Samples with εNd(t) < −10 have more than 60% of alkaline-derived provenance. The Resende Basin was compartmentalized by at least two depocenters separated by a structural high. The depocenters had very proximal sources but were connected by an axial fluvial system. The structural high acted as a barrier, retaining the sediment supply coming from the Itatiaia alkaline massif. These results are compatible with what is seen in other rift-related sedimentary environments, such as the Rio Grande and the North Sea deposits, where Nd and Sr composition of first-cycle clastic sediments reflect their parental source isotopic signature.