Crustal mechanics control the geometry of mountain belts. Insights from numerical modelling

Abstract

Abstract Continental collision forms mountain ranges that have shaped much of Earth's topography. Yet, the process by which material is transported and redistributed in collision zones remains debatable. Here we present a series of two-dimensional thermo-mechanical experiments on continent–continent collision zones to investigate the role of crustal strength in terms of geometry, deformation and exhumation. Depending on the crustal rheology, rate of collision and initial temperature distribution, continental collision may form double vergent orogens or result in continental subduction. Double vergent orogens are characterized by subduction of the lithospheric mantle, diffuse fore- and highly localized retro-shears, elevated topographies, and exhumation of high grade metamorphic rocks. In contrast, continental subduction results in subduction of lower continental crust, the formation of a wedge shaped Moho, a foreland propagating deformation zone, “lower” topographic build-up and exhumation of low grade metamorphic rocks. It is the combination of strength variations and ambient conditions that determines the geometry of mountain belts. Strong rheological coupling of upper and lower crust forms double vergent orogens; low rheological coupling of upper and lower crust results in continental subduction.