Abstract

The interactions between climate, tectonics and surface processes have become a research hotspot in Earth science in recent years. Although various insights have been achieved, the relative importance of climatic and tectonic forcing in influencing the evolution of mountain belts still remains controversial. In order to investigate the tectonic and topographic evolution, as well as the formation mechanism of the eastern Himalayan syntaxis, we developed a comprehensive 2D climatic-geomorphological-thermomechanical numerical model and conducted over 200 experiments to test the influences of convergence rate, average precipitation and initial geothermal gradient on orogenic wedge. The results indicate that, for a specific orogenic wedge, its tectonic and topographic evolution primarily relies on the relative strength of tectonic and climatic forces, rather than their respective magnitudes. A syntaxis is the result of the combined effects of tectonic forces, climatic forces and geothermal field. In mountain belts, once the convergence rate and average precipitation fall within a Type D zone determined by the crustal thermal structure, a sustained, stationary, localized and relatively rapid erosion process will be established on the windward flank of the orogenic wedge. This will further induce sustained and rapid uplift of rocks, exhumation and deformation, ultimately forming a syntaxis. In this context, syntaxis is the inevitable system's outcome under various physical laws, including conservation of mass, momentum and energy, rheology, orographic precipitation, surface processes, etc. Orogens are best viewed as complex open systems controlled by multiple factors, none of which can be considered as the sole cause of the system's outcome.