Temporal and spatial denudation trends in the continental margin of southeastern Brazil

Abstract

The passive margin of southeastern Brazil is characterized by two coast-parallel mountain ranges, Serra do Mar and Serra da Mantiqueira, separated by valleys partially covered with Cenozoic basins. These mountains record fast rock uplift episodes tens of millions of years after the Early Cretaceous continental rifting which are correlated to high sediment influx to the offshore basins. In order to understand how the landscape has been evolving from these events, we integrated new apatite U-Th-Sm/He (AHe) data to a broad apatite fission track (AFT) dataset. Indeed, we performed a model for modern erosion rates based on the relationship of 10Be-derived erosion rates and topographic and climatic parameters. Thermal modeling, together with the published AFT ages, indicate widespread denudation following the Atlantic rift and a peak at Late Cretaceous associated with the alkaline magmatic intrusions and a high-relief extended proto Serra do Mar. From Late Cretaceous and along Cenozoic, Precambrian shear zones and transfer zones seem to exert control in long/short-time denudation rates and delimitates the start position of escarpments. The erosion map shows that modern erosion is focused on the current escarpments and the incised rivers with rates as high as the long-term ones. These rates point to the mobility capacity of the escarpments which have migrated against the low-relief plateaus during Miocene times. In the elevated plateaus, the ongoing surface uplift, disconnection with general baselevel and the loose of drainage area due the escarpment advance, have led to local-relief and erosion rates decreasing, as well as to the weathering profile deepening. Overall, the data suggest that the topographic arrangement between escarpment/low relief highland areas has continuously changed position in space over time, which occurs under control of the Precambrian shear zone and transfer zone reactivations.