Tonian island arc remnants in the northern Ribeira orogen of Western Gondwana: The Caxixe batholith (Espírito Santo, SE Brazil)

Abstract

The Tonian Serra da Prata magmatic arc is part of an association of several magmatic arcs of the Ribeira orogenic system in Southeastern Brazil. Along with the Cryogenian Rio Negro arc, the Serra da Prata arc represents an intra-oceanic arc system while the Ediacaran Rio Doce arc represents an active continental margin arc. Here, we characterize the northernmost segment of the Serra da Prata arc, based on lithochemical and isotopic (whole-rock Sm-Nd and Rb-Sr, and zircon U-Pb and Lu-Hf) data from the Caxixe batholith, located in Espírito Santo State. The Caxixe batholith mostly consists of granodioritic to granitic and minor tonalitic to gabbroic rocks, with calc-alkaline, metaluminous to slightly peraluminous, magnesian, I-type signature and magmatic arc affinity. The rocks display LREE enrichment, positive to slightly negative Eu and negative Nb-Ta anomalies. Zircon U-Pb (LA-ICP-MS and SHRIMP) data reveal magmatic crystallization ages from 859 ± 7 Ma to 847 ± 8 Ma (for zircon cores) and a probably metamorphic age of 834 ± 9 Ma (for zircon rims). Hf Isotopic data yield positive εHf(t) values between +10 and +14, and TDM Hf model ages from 1.01 Ga to 0.84 Ga, in agreement with whole-rockNd and Sr data with εNd(t) values from +0.9 to +6.4 and TDM Nd model ages between 1.2 Ga and 0.8 Ga, and 87Sr/86Sr(i) of 0.6979–0.7035. Our data characterize a juvenile magmatic arc with striking mantle contribution, formed on a supra-subduction intra-oceanic setting similar to modern island arcs. As a whole, the Serra da Prata juvenile arc points to a large ocean that underwent intra-oceanic subduction in the Early Tonian. As a corollary, the Angola, Congo – São Francisco and Paranapanema paleocontinental blocks should be far from each other during the Early Tonian, separated by that large ocean. In a broad scenario, involving ophiolites and juvenile arcs of southern and central Brazil, several cratons of Western Gondwana once had been parts of paleocontinental pieces separated by very extensive Tonian-Cryogenian oceanic realms, including the Neoproterozoic Goiás–Pharusian and Adamastor oceans.