3D numerical modelling of the dynamic of the relief of African passive margins: implications for sedimentary systems and surface transfers
Résumé
The African continent is bordered by passive margins preserving the terrigeneous sediment resulting from its erosion, and as such, recording the dynamics of its relief variation. The thermal evolution of the stretched lithosphere, surface processes (erosion/sedimentation) and flexural isostatic compensation induce vertical movements of the passive margin that can also be altered by the superposition of vertical movement induced by flow in the mantle or tectonically driven deformation. Our objective is to quantify the expression of these different types of vertical movements in the stratigraphic architecture of passive margins basins in general, and around the African continent in particular. The novel aspect of our approach is to integrate the evolution of both domains in erosion and in sedimentation, in a 3D framework involving state of the art numerical modeling tools of the thermo-mechanical evolution of the lithophere (Flex3Dstrati, developed by J. Braun) and advanced concepts in sequence stratigraphy. We define the reference geometry of a passive margin for the numerical modelling by compiling the geometry of peri-atlantic margins from published data. We then performe a parametric analysis to quantify the influence of the initial geometry of the stretched lithosphere (e.g. length of the stretched lithosphere, initial geothermal gradient, necking depth) on the topographic evolution of the margin and the stratigraphic architecture (volume of sediment preserved, depositional sequences, etc...). We then compare the predictions of the numerical model to the observed stratigraphic architecture of African passive marginal basins.