Cenozoic dynamics of the African plate with emphasis on the Africa-Eurasia collision

Abstract

We investigate the forces acting on the African plate from about 56 Ma to the present-day. We aim (1) to establish a basis for quantification of the overall dynamics of the Mediterranean/Middle East region and (2) to understand how Africa reacts to temporal variation in the forces associated with the Africa-Eurasia collision. We use the assumption of dynamical equilibrium which implies that at any given time, the net torque of forces on Africa's northern margin must have been balanced by the other torques acting on the plate. Moreover, temporal variation in the forces on Africa's northern margin must have been balanced by contemporaneous changes in one or more of the other torques. By quantifying those "other" torques we may derive a constraint on the forces at the northern margin. We expect the Africa-Eurasia collision to have been associated with changes in the associated forces and examine how these changes are balanced. Using alternative parameterizations, we calculate the net torque of ridge push, transform fault resistance, and basal drag. We also quantify changes in the torque of forces associated with the continent-ocean transition. The results constitute a framework for detailed dynamic models of the Africa-Eurasia convergence zone. Temporal changes in the ridge push torque prove to be small. The torque of transform resistance does change, but these changes do not relate to forces at the northern margin. Evidence for a relation with collision is found only for the case of basal drag. The results point to a mechanism where the plate maintains its dynamical equilibrium mainly through collision-induced changes in absolute motion. Copyright 1999 by the American Geophysical Union.