Exhumation of the Eastern Himalaya Syntaxis and Tilting of the Eastern Gangdese Batholith: Numerical Simulations

Abstract:

The Eastern Himalaya Syntaxis (EHS) is one of the fastest exhuming regions on Earth since ~10 Ma. While multiple models such as crustal buckling, basal indentation, adjustment of river incision, and tectonic aneurysm have been proposed to explain the evolution of the EHS, the mechanism of its fast exhumation is still under debate. In this study, we perform numerical simulations to test several end-member models of exhumation using a 2-D thermo-mechanical finite difference code implemented with visco-elasto-plastic rheology and particle-in-cell approach. Unconventional from many other studies that focus on the exhumation of the EHS itself, we incorporate recently established bedrock pressure pattern in the eastern Gangdese Batholith to test if the exhumation of the EHS is capable of tilting the surrounding crust, as well as explore how surface erosion affect the dynamics of the lithosphere. Preliminary results for a rapid and focused surface erosion (10 km/Myr) end-member case indicate on the timescale of ~10 Myr, lower crust of >10-15 kbar can be exhumed to the surface. The local thermal gradient is elevated and crustal viscosity is drastically reduced due to erosion-driven advection. For a lower crust of plagioclase rheology, the exhuming crust forms a vertical conduit with an exhumation rate of ~10 km/Myr. Lateral flow of the lower crust into the EHS is also observed. This model produces an antiform beneath the EHS with a regional bedrock pressure gradient increasing towards the locus of focused erosion. While initial modeled results show promising similarities with field observations, we are performing more systematic simulations to understand the dynamics.