Thin-viscous-sheet models have proved to be very useful in exploring the interaction between plate boundary and gravitational forces during continental collision. However, simplifications of these models (e.g., absence of faults, planar geometry of the collision zone) limit their use in making specific predictions regarding tectonic evolution, such as the role of eastward extrusion along major strike-slip faults during the Indo-Asian collision. This deficiency is overcome by a thin-shell finite-element model with faults that can assess the effects of preexisting fault configurations and topographic distributions on velocity fields. Numerical simulations of a palinspastically restored Asia at ca. 50 Ma suggest that preexisting lithospheric weaknesses favor north-south shortening during initial collision, whereas preexisting high topography in southern Asia promotes eastward extrusion. These results underscore the first-order importance of initial topography and the distribution of preexisting faults in the outcome of geodynamic modeling.

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