Abstract

Plate reconstruction studies show that the Neotethys Ocean was closing due to convergence of Africa and Eurasia towards the end of the Cretaceous. The period around 75 Ma reflects the onset of continental collision between the two plates, although convergence was still mainly accommodated by subduction, with the Neotethys slab subducting beneath Eurasia. Africa was separated from the rapidly north moving Indian plate by the Owen oceanic transform in the northeast. The rest of the plate was surrounded by mid-ocean ridges. Geologic observations in large basins show that Africa was experiencing continent-wide rifting related to northeast-southwest extension. We aim to quantify the forces and related paleostresses associated with this tectonic setting. To constrain these forces, we use the latest plate kinematic reconstructions, while balancing horizontal gravitational stresses, plate boundary forces and the plate's interaction with the underlying mantle. The contribution of dynamic topography to horizontal gravitational stresses is based on recent mantle convection studies. We model intraplate stresses and compare them with the strain observations. We find that slab pull, horizontal gravitational stresses and transform shear tractions in general acted with the same orientation as the absolute motion of the African plate 75 Ma. Both the balance between these three and the other, resistive, forces, and the fit to strain observations require the net slab pull, as experienced by the plate, to be low, pointing to the absence of a mature continuous Neotethys subduction zone at the time. This corresponds well to reconstructions of micro-continents interfering with the Neotethyan subduction.