Effect of inherited structures on continental breakup: A multi-scale modeling approach

M. KNOLL; A. TOMMASI; J.W.SIGNORELLI; R.E. LOGÉ

Vienna

Congreso; European Geosciences Union Annual Meeting; 2008

Major rifts that lead to continental breakup end to form parallel to ancient orogenic belts, such as the East African, North and South Atlantic rifts. During this process, ancient lithospheric structures are systematically reactivated, suggesting that the preexisting structuration of the lithosphere influences rift propagation.The initiation of rifting is generally temporally and spatially linked to mantle plume, but there is a paradox between the axisymetric thermal perturbation and stress field produced by the upwelling plume and the planar geometry of rift. Seismic and electrical anisotropy measurements as well as observations on xenoliths shows that a strong lattice preferred orientation (LPO) of olivine exists in the lithospheric mantle. We propose that this olivine LPO, developed during past tectonic events and frozen in the lithospheric mantle since then, is the main parameter controling the lithosphere deformation. In order to study the effect of an inherited LPO and its evolution during the deformation on the continental break-up process, we use a multi-scale model in which an anisotropic viscoplastic simulation of the deformation of a polycrystal is coupled with a 3D finite element code. A multi-domain meshing tool is used to define zones with particular different initial structures and LPO. We model the extensional deformation of a continental plate composed of various regions displaying different initial fabrics. Results show a heterogeneous deformation, characterized by a strong strain localisation.The initial texture controls both the initiation and the propagation of the deformation, leading to development of shearing parallel to the pre-existing shear zones in the plate.