The Role of Subduction‐Induced Subsidence in the Evolution of the Karoo Basin

Abstract

The stratigraphic record indicates that during the Late Carboniferous to Early Triassic, South Africa experienced an episode of large‐scale subsidence that resulted in the development of the Karoo Basin. The southern margin of the region was contemporaneously dominated by an episode of compressional tectonics, and there is evidence for subduction of the paleo‐Pacific plate beneath the Karoo Basin. We propose that the long‐wavelength component of the basin subsidence resulted from the deflection of the lithosphere due to mantle flow coupled to the adjacent subduction. This was followed by a recovery phase during which the entire region was uplifted on cessation of subduction (and subsequent loss of dynamic support for subsidence), contributing to the present‐day high‐elevation topography of South Africa. Numerical models of mantle convection are presented and show that a shallow‐dipping slab is able to reconcile the observed long‐wavelength subsidence of the basin. A significant component of the near‐field sedimentation is also explained by the model; however, matching the total stratigraphic record in this region requires the tandem effects of subduction‐induced deflection and flexural thrust loading of the lithosphere.