Numerical models of induced mantle flow applied to lithospheric delamination and oblique slip partitioning

We model induced mantle flow in two tectonic processes: lithospheric delamination and oblique slip partitioning. We assume a constant Newtonian viscosity and uniform density for the mantle, with flow driven by the motion of the rigid lithosphere.;To approximate lithospheric delamination, we separately model the sinking of a disk and an infinite strip into the mantle from near the lithospheric lid. Near the lid, the object's sinking velocity is proportional to the cube of the gap thickness; thus delamination initially proceeds very slowly. The strip at first sinks 3/4 as fast as the disk, implying that delamination slightly favors an equidimensional root, rather than a long, linear one.;Suction induced between the sinking disk and the lid creates a downward load on the lithosphere. We calculate the isostatic response to this load. We find reasonable agreement between our model and exhumation data from the Himalayas. However, our analysis assumes spatially uniform erosion. In reality, erosion rates must be highest at the edges of the plateau, where there is high relief. Our plateau should therefore be higher in the center than at the edges, a result that does not match the topography of Tibet.;Next, we study the effect of the asthenospheric wedge in oblique subduction zones on the location of the partitioning strike-slip fault. We treat the trench-parallel component of subduction as antiplane flow, driven by relative motion between the lid and the slab. The shear stress resolved on the overriding plate varies inversely with distance from the corner.;We integrate the shear stress, assuming zero stress beyond the length of the subducting slab. This gives us the shearing force on any vertical plane through the lithosphere, which is infinite at the corner because of the velocity singularity we impose there, but drops below lithospheric strength within a few kilometers. Thus the strike-slip fault forms very near the asthenospheric corner. Since the volcanic front coincides with this fault in most regions of oblique subduction, the volcanic front probably lies nearly above the asthenospheric corner.