Accelerated denudation and tectonic/geomorphic reactivation of the cratons of northeastern Brazil during the Late Cretaceous

Abstract

Apatite fission track (AFT) data for a suite of 40 outcrop samples from the São Francisco and eastern Guaporé cratons in northeastern Brazil record between 60° and 100°C of cooling since the separation of South America and Africa at ∼130 Ma. Quantitative thermal histories derived from the data indicate two discrete phases of cooling: the first is coeval with continental breakup at ∼130 Ma and the second is broadly coincident with the change in relative plate motion at ∼60–80 Ma. The thermal histories indicate an increase in the average rate of denudation at ∼60–80 Ma over much of the interior of northeastern Brazil. Estimated total amounts of postbreakup denudation vary between 3 and 7 km, with greater amounts occurring along the eastern and northern margins of the São Francisco and Guaporé cratons, respectively. Two samples within the Pernambuco shear zone yield anomalously young AFT ages which record cooling caused by locally enhanced denudation rates during the Late Cretaceous. The timing and style of the Late Cretaceous tectonic event in Brazil is similar to the analogous Late Cretaceous history of the central African shear zone system in Africa. This suggests that both events were associated with intracontinental deformation caused by major changes in the relative plate motions between Africa, Antarctica, and South America that began between anomaly C34 (83 Ma) and C31 (67 Ma).