PLATE MOTION AND DRAGGING OF THE UPPER MANTLE - LATERAL VARIATIONS OF LITHOSPHERIC THICKNESS AND THEIR IMPLICATIONS FOR INTRAPLATE DEFORMATION

The impact of lateral variations in the thickness of the lithosphere on surface topography, horizontal intraplate deformation and stress accumulation is studied for plates that drift with respect to the highly viscous lower mantle and the transition zone. The lithosphere and upper mantle are described by a viscoelastic Maxwell rheology within the frame-work of a finite element scheme which allows the modeling of heterogeneous lithospheric structures in 2D vertical cross sections. The geophysical signatures are found to be extremely sensitive to lateral viscosity contrasts which interact with the upper mantle flow. This mechanism can contribute to a certain extent and in concert with the other driving forces of plate tectonics to the evolution of back-arc basins, to the explanation of the largest angle of subduction in west-dipping slabs and to the initiation of subduction of an oceanic lithosphere underneath a stable continental one.