Influence of viscosity pressure dependence on deep lithospheric tectonics during continental collision

Abstract

AbstractPrevious geodynamic models of continental collision show that the behavior of the continental lithosphere is strongly influenced by its rheology. We build on previous work by quantitatively investigating with numerical experiments the influence of the pressure dependence of viscosity on the process of tectonic deformation during collision. The models demonstrate how the inclusion of viscosity pressure dependence can quite substantially alter the style of continental mantle lithosphere deformation. At low activation volumes, high convergence rates, and low to moderate initial Moho temperatures, the subduction style of mantle lithosphere deformation is dominant. Increasing the activation volume of mantle material allows the subduction style of deformation to occur at all convergence rates studied in the experiments, at the expense of the subduction‐drip and ablative‐drip styles of deformation. At low activation volumes, high convergence rates, and high initial Moho temperatures, the distributed pure shear style of deformation occurs. With these same conditions, increasing the activation volume of mantle material produces an ablative subduction style of mantle lithosphere deformation. At low activation volumes, low convergence rate, and moderate to high initial Moho temperatures, the mantle lithosphere prefers a convective removal style of deformation; increasing the activation volume here yields an ablative‐drip and distributed pure shear styles of deformation. The results demonstrate that inclusion of the pressure dependence of viscosity—quite often neglected in lithosphere‐scale geodynamic models—can be significant in modulating deformation of the deforming lithosphere.