EVALUATING THE ROLE OF PREEXISTING WEAKNESSES AND TOPOGRAPHIC DISTRIBUTIONS IN THE INDO-ASIAN COLLISION BY USE OF A THIN-SHELL NUMERICAL-MODEL

Thin-viscous-sheet models have proved to be very useful in exploring t he 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 duri ng the Indo-Asian collision. This deficiency is overcome by a thin-she ll finite-element model with faults that can assess the effects of pre existing fault configurations and topographic distributions on velocit y fields. Numerical simulations of a palinspastically restored Asia at ca. 50 Ma suggest that preexisting lithospheric weaknesses favor nort h-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 d istribution of preexisting faults in the outcome of geodynamic modelin g.