Role of surface processes and deep crustal rheology in the steady-state LongMenShan building: Insights from geodynamic modeling

It is widely accepted that the horizontal tectonic forces and lateral rheological contrast control the strain localization and, consequently, the evolution of mountain ranges. However, in active orogenesis involving massive surface materials redistribution, to what extent and in which way do surface processes and strong contrast in vertical rheological properties manage the stress transmission and strain partitioning, have been the subject of critical debate and discussion. The LongMenShan (LMS) area exhibits the steepest topographic gradient around the Tibetan Plateau. Understanding the interplay among the abnormal steep relief, slow convergence rate, and rapid erosion rate is crucial for comprehending how surface processes and vertical rheological configurations contribute to the evolution mechanisms of the Eastern Tibetan Plateau (ETP). In this study, 2-D finite element models were employed to retrieve robust relationships between surface topography and deep material transport in the ETP and LMS. These models considered fundamental mechanical parameters, particularly the erosion rate and mid-crustal rheological configuration. The results indicate that regional tectonization governs the tectonodeformation mechanism and surface geomorphic characteristics of the study area. Differential erosion is shown to significantly influence the shaping of peripheral topography and alter the substantial seismic potential across different faults. Between the LongRiBa Faults (LRBF) and the LMS, the weak mid-crust material decouples the upper and lower crusts via vertical strain partitioning. This decoupling affects the formation of deep detachment structures in the LMS and promotes the brittle shortening of the upper crust, contributing to the region's steep relief. Lastly, our results suggest that channel flow and brittle crustal shortening modes are not mutually competitive but rather coexist in different regions of the ETP and LMS. Deep processes, influenced by inherited lithospheric heterogeneities, play a decisive role during the formation of the ETP and LMS. Our results underscore the importance for understanding the underpinning geodynamic mechanisms that shape the eastern margin of the Tibetan Plateau.