New detrital petrographic and thermochronologic constraints on the Late Cretaceous–Neogene erosional history of the equatorial margin of Brazil: Implications for the surface evolution of a complex rift margin

Abstract

AbstractThe equatorial margin of Brazil is an example of a rift margin with a complex landscape, dominated by an escarpment perpendicular to the continental margin, which testifies to an equally complex rift and post‐rift surface and tectonic evolution. This has been the focus of a long debate on the driving mechanism for post‐rift tectonics and on the amount of exhumation. This study contributes to this debate with new petrographic and thermochronologic data on 152 samples from three basins, Pará‐Maranhão, Barreirinhas and Ceará, on the offshore continental platform. Our detrital record goes back to the rift time at ca. 100 Ma ago and outlines three major evolutionary phases of a changing landscape: a rift phase, with the erosion of a moderate rift escarpment, a Late Cretaceous‐Palaeogene post‐rift phase of major drainage reorganization and significant vertical erosion and a Late Oligocene‐to‐Recent post‐rift phase of moderate vertical erosion and river headwater migration. We estimate that along the equatorial margin of Brazil, over a large onshore area, exhumation since the Late Cretaceous has totalled locally up to 2–2.5 km and since the late Oligocene did not exceed 1 km.