Viscous drag and lateral viscosity heterogeneities: implications for intraplate deformation

We consider the effects of lateral Variations in the thickness of the lithosphere on surface topography, horizontal intraplate deformation and stress accumulation for plates that drift with respect to the highly viscous lower mantle and transition zone. The lithosphere and upper mantle are described by means of a viscoelastic Maxwell theology. A finite element scheme allows us to deal with large viscosity contrasts in the vertical and horizontal directions. Heterogeneous lithospheric structures appropriate a ''Mariana type'' subduction is modeled in a vertical cross sections. The dynamic topography and intraplate deformation, maintained by constant horizontal forces applied at the edges of the drifting plate, are extremely sensitive to lateral viscosity contrasts which interact with the upper mantle flow induced by the relative velocity with respect to the lower mantle. In concert with the other driving forces of plate tectonics the mechanism considered in this paper should be considered a valuable contributor to the evolution of back-arc basins and to the explanation of the largest angle of subduction in west-dipping slabs.