Dynamic topography and lithospheric stresses since 400Ma

We present a model of dynamic topography and lithospheric stresses in a reference frame linked to the fixed Africa since 400 Ma. We start with a simple geodynamical model in which we combine contributions due to subducted lithosphere and to long wavelength upwellings during the last 400 million years. Once built this model of temporal variation of the large-scale mantle heterogeneities, we calculate the associated surface topography and lithospheric stresses and compare them with geological observations. We discuss the temporal evolution of the topographic spectrum and the permanent extensional regime over Africa. Indeed, the Peri-Pacific girdle of subduction creates a large-wavelength positive topography at the center of the ring, that is to say over Africa. The superimposition of this extension with the one induced by the dome at the bottom of the mantle leads to a permanent extensional regime over Africa which creates faults with azimuth directions depending on the direction of the most active part of the ring of subductions. We obtain fractures with an NW-SE azimuth during the period 275-165 Ma, and with an E-W direction, between 155-95 Ma. Finally, during the Mesozoic and the Cenozoic, we correlate the permanent extensional regime over Africa with the observed direction of the rifts.