The evolution of the Neoproterozoic São Gabriel juvenile terrane, southern Brazil based on high spatial resolution U-Pb ages and δ18O data from detrital zircons

Abstract

The São Gabriel terrane is a segment of juvenile crust exposed in the western part of the Dom Feliciano Belt in the southern Mantiqueira Province, southern Brazil. In this study high spatial resolution U-Pb geochronological data for 171 detrital zircons of the Cambaizinho Complex are used to investigate the tectonic evolution of this juvenile terrain. Eighty-one grains were later selected for SIMS δ18O analyses. Ages ranged from 840 to 660Ma, with a strong concentration between ca. 750 and 700Ma. The age spectrum of the detrital zircon grains from this meta-sedimentary succession suggests that the original sediments were derived from the erosion of the arc, most likely in a short-lived syn-orogentic basin. Th/U ratios and internal structures of the zircon grains reveal that they were mostly eroded from the arc magmatic rocks, without any relevant contribution from their metamorphic counterparts, or from any other older source. The δ18O values varied from 3.2 to 9.6‰, indicating the coeval crystallization of both unaltered, pristine mantle magmas alongside altered mantle magmas, and strongly contaminated continental crustal magmas generated in both continental and oceanic arc setting. In summary, our data provides an insight into the progressive evolution of the São Gabriel terrane from an intra-oceanic subduction zone at ca. 879–750Ma to a continental arc setting (ages <690Ma) into three distinct periods, which preceded ocean closure and continental collision at the end of the Neoproterozoic.