Numerical modelling of coupled climate, tectonics, and surface processes on the eastern Himalayan syntaxis

The geosphere dynamics near Earth's surface is a key scientific issue for understanding how Earth system works. However, the specific mechanisms underlying the interplay between these geospheres still remain unclear. Here, we take the eastern Himalayan syntaxis, the most typical region undergoing ferocious geosphere interplay on the planet, as our primary research area. We incorporated a topography-dependent precipitation model into traditional geomorphological-thermomechanical modelling and conducted over 200 experiments to investigate the interplay between climate, tectonics, and surface processes during the evolution of the orogenic wedge. The results show that a distinct type of orogenic wedge emerges when the convergence rate and average precipitation fall within specific ranges determined by the crustal geothermal field. Within this type of orogenic wedge, a sustained, stationary, localized and relatively rapid erosion process can be established on the windward flank. This can further induce sustained and rapid uplift of rocks, exhumation and deformation, forming a large-scale antiform, which exhibits a certain degree of similarity to the eastern Himalayan syntaxis. We propose that the formation of the eastern Himalayan syntaxis share this similar mechanism. Our analysis of the results indicates that the influences of climatic forcing, tectonic forcing, and geothermal field on the evolution of orogenic wedge can be integrated into a single parameter ($E_F$), and we propose that 0.24≤$E_F$≤0.45 is a necessary condition for the development of a syntaxis, which provides a quantitative constraint on the formation of a syntaxis for the first time.