Dynamics of Africa 75 Ma: from plate kinematic reconstructions to intraplate paleo-stresses

Abstract

Towards the end of the Cretaceous, the African plate was mostly surrounded by mid-ocean ridges, apart from the converging northern boundary with Eurasia. The period reflects the onset of collision, although convergence was still mainly accommodated by subduction. The plate was experiencing plate-wide rifting associated with northeast-southwest extension. I use plate kinematics and the criterion of mechanical equilibrium, balancing lithospheric edge forces, body forces and the interaction with the underlying mantle, to constrain the tectonic forces on the plate. The elastic stress responses to the force sets are modelled using the assumption of plane stress on a spherical shell. Comparisons between modelled stresses and geological observations of rifting are used to explore the influence of lithospheric forces on the geological events and deformation. I find that the African plate 75 Ma was mainly driven by slab pull in combination with the body forces produced by the gravitational potential energy (GPE). Although the interaction with the underlying mantle is not necessary to achieve mechanical equilibrium, the correspondence to the rifting observations is significantly better if the driving forces were not only resisted at the subduction zone interface with Eurasia, but also by passive mantle drag at the base of the lithosphere. The mechanical equilibrium also dictates that the net slab pull acting on the plate was relatively low, indicating that the slab was either experiencing unusually strong support in the mantle or the transmission of the slab pull forces to the rest of the African plate was inhibited.