Thermal evolution of the southeastern Brazilian continental margin

The southeastern Brazilian continental margin has a debated evolution regarding postrift events and formation of topography. Apatite fission track (AFT) and apatite U-Th/He (AHe) analysis ages for the N-S transect between Rio de Janeiro and Três Rios range between 98.5±11.9 and 54.1±4.2 Ma. Ages are younger towards the coast and increase progressively inland. Highest samples (around 1500 m above sea level) have older AFT ages. A wide range of ages was not found in the area, contrasting with the large AFT age span found by other studies in adjacent portions of the Brazilian continental margin, where age ranges of up to ~200 Ma from the coast to the innermost sample in the continent have been reported. The cooling ages and the thermal history models produced with software QTQt corroborate a uniform and continuous cooling process for the rifted margin, with total depths of denudation between 2.5 and 4.4 km, attesting to the absence of post-Cretaceous rift reburial in the area. Towards the continental interior, at the back of the Serra do Mar escarpment, thermal history models point to a change in cooling rate in the Upper Cretaceous, compatible with reported reactivation of the regional Neoproterozoic structures which led to the formation of the Cenozoic Rift System of Southeastern Brazil. Collision episodes in the western margin of W Gondwana have important role on platewide stress distribution, inducing regional structure reactivation and creation throughout the South American Platform. The plate-wide deformation arising from the western plate margin collisions is possibly responsible for the formation of the many Paleozoic grabens, which were the precursors of the cratonic basins of the South American continent. Among those, evidence from zircon U-Pb detrital provenance indicates that the Ordovician Piranhas Graben in central Brazil is in fact an early manifestation of the Paraná Basin, since its progressive increase in catchment area matches the sediment sources of the Silurian Vila Maria and Devonian Ponta Grossa formations of the Paraná Basin. The present-day landscape is mainly a result of isostatic rebound due to erosional unloading, although combined with post-rift magmatism and regional structure reactivation. The post-rift continuous uplift of the southeastern Brazilian margin supplied vast volumes of clastic sediments to the Santos and Campos basins during the late Cretaceous and Cenozoic, generating high quality reservoirs for hydrocarbons.