Numerical models of the interaction lithosphere/mantle

Recent advances in computational geodynamics give directions to solving the coupled lithosphere deformation/convecting mantle problem. At the heart of this lies the "subduction" theme, which deals with cold solid lithosphere plunging into a convecting fluid like substance. Lithosphere dynamicists tend to assume that to first order subduction is governed by the rheology of the lithosphere itself responding to the negative buoyancy forces arising from it. Convection dynamicists solve the problem more comprehensively by acknowledging plasticity within the lithosphere as well as flow in the deeper mantle. Unfortunately, the solid mechanical database is neglected in those more comprehensive approaches. Here, the problem is solved in a somewhat mixed approach, i.e. a solution is presented in which a coupled solid-mechanical /fluid-dynamic lithosphere rides on a passive mantle (without active convection). The setup is used to investigate self-consistently the problems of subduction initiation, the subsequent "freely" falling slab and the interaction with the 660km discontinuity. The approach gives new insights into coupling/decoupling of deformation within the lithosphere as a function of wet/dry rheology during subduction initiation, the "elasticity" of the slab, its coherency and subduction angle as well as the penetration or non-penetration problem of slabs into the 660km discontinuity.