Flexure of the lithosphere and the geodynamical evolution of non-cylindrical rifted passive margins: Results from a numerical model incorporating variable elastic thickness, surface processes and 3D thermal subsidence
Résumé
We present a new numerical model to calculate the surface deflection of a two-dimensional, yet variable thickness, thin elastic plate. The model is based on a multi-grid, finite difference solution of the fourth-order differential equation that incorporates the terms arising from the non-uniform thickness assumption. The model has been developed to calculate the flexural response of the continental lithosphere subjected to an arbitrary, instantaneous stretching. The flexural model is coupled to (a) a finite element, three dimensional thermal model incorporating the conduction, advection and production terms that allows the computation of the thermal subsidence resulting from the stretching-induced perturbation of the isotherms, assuming that the effective elastic thickness is controlled by the depth to a given isotherm; and (b) a finite difference surface process model that assumes that transport is linearly proportional to slope leading to a second-order, diffusion-type partial differential equation. The model also incorporates the effect of sediment compaction. We present a series of simple benchmarks that demonstrate the accuracy of the model. We also present results of simple 2D and 3D stretching experiments highlighting the importance of 3D flexural effects and the assumed variable elastic thickness on the development of a passive margin and its thermal evolution. Finally, we perform a numerical experiment based on a stretching geometry derived from the present-day geometry of the Western AfricaTransform Margin to predict sediment accumulation patterns and a stratigraphic architecture which we can compare to observations.