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.