U–Pb and Lu–Hf isotopes applied to the evolution of the late to post-orogenic transtensional basins of the dom feliciano belt, Brazil

Abstract

The Santa Bárbara and Guaritas Groups, located in southern Brazil, represent the last episode of deposition in the Camaquã Basin, which included deposition of sandstone, siltstone and conglomerates during the late Neoproterozoic and Eopaleozoic as part of the collisional period of the Brasiliano/Pan-African Orogeny. Combined U–Pb and Lu–Hf analyses of detrital zircon grains from outcrops and drill holes in both groups together with an analysis of paleocurrent data provide information regarding the sedimentary provenance and tectonic evolution. The U–Pb geochronological data from both groups include concordant ages that are predominantly Paleoproterozoic and Neoproterozoic, with an increasing contribution by Early Neoproterozoic and Paleoproterozoic zircon grains in the upper unit, the Guaritas Group. The maximum depositional age of the basal siltstone units of the Santa Bárbara Group is 567.9±5.9Ma, and the maximum depositional age of the Guaritas Group is 540–535Ma. The Lu–Hf model ages (TDM) indicate that the zircon grains in both groups display a predominantly Archean and Paleoproterozoic inheritance, with predominantly negative ɛHf values, which indicates that the source rocks originated from the subcontinental lithosphere.