Tilting of continental interiors over a source of dynamic topography : Late Cretaceous erosion of the South African plateau

Abstract : New sedimentary flux data confirm the observation that a large pulse of erosion affected the South African Plateau in the late Cretaceous. This episode of rapid erosion (less than 30 Myr) is likely to be related to a major uplift phase that is apparently difficult to reconcile with a possible mantle origin, namely the presence of low density body in the underlying mantle causing flow and dynamical uplift of the continent. Given its size, the growth and rise of this so-called "African superswell" is likely to have taken one to several hundred million years. Here we demonstrate by using a simple model for fluvial erosion that tilting of the continent as it rides over a wide source of dynamic topography can not only cause uplift of the plateau but also lead to substantial erosion of large surface areas in a relatively short amount of time, because the tilting produces a continental-scale drainage re-organization. We show that embedding a lithological contrast, such as the one that might have existed between a thick layer of Karoo volcano-clastic sediments overlying basement, greatly amplifies the rate of erosion (and sedimentation) during the tilting episode.We demonstrate that our scenario is consistent with paleogeographic reconstructions of the position of the African continent with respect to the African superswell, the temporal and spatial evolution of kimberlite eruptions across southern Africa and the past and present-day highly asymmetrical drainage geometry.