Impact of Lithospheric Strength Distribution on India‐Eurasia Deformation From 3‐D Geodynamic Models

Abstract

AbstractModels for continental lithospheric strength are not well resolved due to a lack of direct measurement; however, numerical simulations provide means for evaluating the physicality of endmember cases. We simulate the 3‐D dynamics of continental lithosphere within the India‐Eurasia collision zone and compare results to observed deformation. Three‐dimensional lithospheric deformation is approximated with creeping flow in a layered spherical cap. We partition strength with depth according to endmember models, using laterally varying estimates of vertically averaged effective viscosity to constrain the absolute values of 3‐D viscosity in the upper crustal and mantle layers. Comparisons between dynamic solutions and observed geophysical data indicate: (1) Deformation within the subducted Indian slab is required to simulate uplift along the entire Himalayan front with 1022 Pa·s representing an upper bound for slab strength. (2) Along‐strike variations in crustal strength are necessary to match surface observations. (3) Balance of gravitational forces acting on Tibetan lithosphere with a weak lower crust are able to replicate observed vertical deformation patterns. A west‐to‐east decrease in the lateral extent of the underthrust Indian slab is required for reproducing observed surface motions in Tibet. Geodynamic simulations yield subsidence in southern Qiangtang and Southeast Asia consistent with global positioning system‐derived dilatation. We note a trade‐off between upper crustal strength and surface velocity rotation around the Eastern Himalayan syntaxis. Simulations with stronger upper crust replicate velocities in western Tibet but not the east, while those with weaker upper crust produce observed rotation in eastern Tibet but overpredict magnitudes to the west.