Deformation and exhumation in thick continental crusts induced by valley incision of elevated plateaux

Abstract. Surface processes such as erosion and sedimentation play a critical role in crustal deformation, particularly in actively deforming orogenic belts. While these processes have been extensively studied in large-scale erosive and tectonically active regions, the specific effects of valley incision on crustal deformation, especially in tectonically inactive regions, remain poorly understood. In this study, we hypothesize that crustal deformation induced by valley incision is primarily governed by three parameters: incision velocity, crustal thickness, and the elevation difference between the plateau and the valley base level. Using two-dimensional (2D) thermomechanical models, we investigate the influence of valley incision on crustal deformation and exhumation by varying these parameters. Our results show that valley incision alone can induce significant crustal deformation, associated with lateral viscous flow in the lower crust leading to near-vertical channel flow and extensional brittle deformation in the upper crust below the valley. This deformation leads to lower-crust exhumation, within a 10 Myr time frame, if crustal thickness is greater than 50 km, the initial plateau elevation is greater than or equal to 2 km, and the long-term effective erosion rate exceeds 0.5 mm yr−1. Furthermore, while the onset of lower-crust exhumation is primarily controlled by the initial plateau elevation, the total amount of exhumed lower crust after 10 Myr strongly increases with the initial thickness of the lower crust which favors viscous flow. Moreover, natural systems that exhibit the required crustal thickness, plateau elevation, and erosion rates for lower-crustal exhumation, as highlighted in our models, also demonstrate active lower-crustal exhumation, as is the case in regions such as Nanga Parbat and Namcha Barwa. These findings offer new insights into the coupling between surface processes and deep crustal dynamics, highlighting the potential for valley incision to drive substantial crustal deformation and promote lower-crustal exhumation.