A COMPARISON OF THE DYNAMICS OF NORTH AMERICA AND THE INDIA-EURASIA COLLISION

Both western North America and Asia exhibit broad diffuse zones of continental deformation. Recent acquisitions of geodetic and seismic data have enabled new constraints for crustal and upper mantle structure, along with measurement of relative motions and strain patterns, within parts of North America and Asia. Although the kinematics of the deformation fields within both regions are becoming increasingly well-defined, the dynamics of these regions remains enigmatic. Still unknown is the rheology, both its vertical and lateral variations within crust and mantle. The detection of both vertical and lateral rheological variations remains a significant challenge in linking kinematics with dynamics. The incorporation of reliable structural information also remains challenging. We use large-scale global lithospheric models, coupled to global mantle circulation models, to investigate the dynamics of both plate boundary zones. We test a number of simple rheological models involving lateral variations of depth-integrated effective viscosity within the lithosphere, and radial variations in rheology for the mantle. Topography, along with crustal and lithosphere structure models, provide input for lithospheric body forces. Tomography models provide constraints for mantle circulation patterns, generated using full 3-D mantle flow calculations. We test 36 different tomography models and score the total dynamic response with kinematic indicators such as strain patterns, surface motions, and stresses from the World Stress Map database. We also investigate the match with predicted and observed geoid patterns. The two plate boundary zones display distinct differences, yet they also share similarities. Both plate boundary zones are impacted by large-scale mantle flow patterns associated with the history of subduction. For the India-Eurasia collision zone in particular, this mantle flow plays a key role in driving India-Eurasia convergence. Extension patterns within both plate boundary zones are strongly influenced by crustal and upper mantle structure, which controls gradients in gravity potential energy differences.