Tectonic Controls on Along-Strike Topographic and Structural Variations in the Himalaya: a Numerical Modeling Study.

Abstract:

Although the Himalayan range is traditionally presented as cylindrical, its geological structure, topography, precipitation, and exhumation patterns all vary significantly along-strike. The potential climatic or tectonic controls on these spatially variable topographic, precipitation and exhumation patterns have been widely discussed in recent years. A growing body of data suggests that variations in the geometry of the main Himalayan detachment (in particular the presence or absence of a major mid-crustal ramp) strongly control the kinematics, exhumation and topography of the orogen. However, what controls these variations in detachment geometry and their possible temporal evolution remains unclear. Here we report new thermo-mechanical modeling results to address these issues. We model the evolution of the Himalayan fold-and-thrust belt over the last ~30 Myr, focusing on the role of rheology and pre-existing structures in controlling this evolution. Our model results lead us to propose a scenario for the formation of Greater Himalayan klippen within the Lesser Himalayan fold-and-thrust belt and suggest a transient temporal evolution of the structure and topography of the fold-and-thrust belt in response to ramp formation at the orogenic front and subsequent migration toward the orogen interior. These results suggest that asynchronous ramp underthrusting in different segments of the range could control along-strike variations in topography, structure and exhumation of the mountain belt.