Geochemistry, Sm-Nd isotopes and SHRIMP U-Pb geochronology of the morro do coco granite (RJ, Brazil): Another piece of the post-collisional magmatism of the ribeira belt

Abstract

Te Morro do Coco granite (MC) is a post-collisional intrusive body that was emplaced at Ribeira Belt, in the Cambro-Ordovician, succeeding the fnal stages of the Gondwana supercontinent amalgamation. Tis unit requires more studies, contrasting with similar best investigated occurrences of the central Ribeira Belt. Tis work presents a detailed investigation of such unit using petrography, Inductively Coupled Plasma (ICP), X-Ray Fluorescence (XRF) whole-rock geochemistry, U-Pb (SHRIMP) geochronology and Sm-Nd isotopes. Te rock is a nearly undeformed syenogranite, geochemically classifed as a high-K calc-alkaline magnesian, with metaluminous to slightly peraluminous afnity. Strongly light rare earth elements (LREE)-enriched paterns with signifcant negative Eu anomalies, typical of post-collisional granites, are identifed. Similarly to other post-collisional granites of the central Ribeira Belt, U-Pb zircon data provide crystallization age of 496 ± 3 Ma. Sm-Nd isotopic data suggest crustal magma source as indicated by eNd(496) of-9, 143Nd/144Nd ratios between 0.511747 and 0.511752 and Mesoproterozoic TDM ages of 1.3 Ga. Based on its geochemical characteristics, morphology and geochronology, this unit is considered here as a member of Nova Friburgo Suite. Geochronological data defned three pulses of magmatism in this part of the orogen during the Cambro-Ordovician (515, 490 and 460 Ma).