Growth of Collisional Orogens From Small and Cold to Large and Hot—Inferences From Geodynamic Models

Abstract

It is well documented that the interplay between crustal thickening and surface processes determines growth of continent-continent collision orogens from small and cold to large and hot. Additionally, studies have demonstrated that the structural style of a mountain belt is strongly influenced by inherited (extensional) structures, the pattern of erosion and deposition, as well as the distribution of shallow detachment horizons. However, the factors controlling distribution of shortening and variable structural style as a function of convergence and surface process efficiency remain less explored. We use a 2D upper-mantle scale plane-strain thermo-mechanical model (FANTOM) coupled to a planform, mass conserving surface-process model (Fastscape), to investigate the long-term evolution of mountain belts and the influence of lithospheric pull, extensional inheritance, surface processes efficiency, and decoupling between thin-and thick-skinned tectonics. We establish an evolutionary shortening distribution for orogenic growth from a mono-vergent wedge to an orogenic plateau, and find that internal crustal loading is the main factor controlling the large scale evolution, while lithospheric pull modulates the plate driving force for orogenesis. Limited foreland-basin filling and minor exhumation of the orogen core are characteristic for low surface-process efficiency, while thick foreland-basin fill, and profound exhumation of the orogen core are characteristic for high surface-process efficiency. Utilizing a force balance analysis, we show how inherited structures, surface processes, and decoupling between thin-and thick-skinned deformation influence structural style during orogenic growth. Finally, we present a comparison of our generic modeling results with natural systems, with a particular focus on the Pyrenees, Alps, and Himalaya-Tibet.