Drainage evolution in accretionary thrust systems as responses to tectono-climatic variability: Insights from sandbox modelling

Abstract

Orographic evolution is a dynamic process that unfolds as structural deformation and climate-driven surface processes interact. In these topographic regions, the intricate ways in which fluvial processes respond to tectonics and climate require a more quantitative investigation. Given the inherent challenges in directly observing these evolutionary processes in nature, here we employ an analogue sandbox modelling approach to explore the dynamic interplay among orographic evolution, structural deformation and climate-driven surface processes within accretionary thrust systems across a spectrum of tectono-climatic conditions. Specifically, we investigate how the development of drainage and the evolution of fluvial processes adapt to varying tectonic shortening rate and precipitation. The results show that the formation and orientation of longitudinal rivers are not solely dictated by structural elements such as faults or folds; they are also significantly influenced by the configuration of alluvial fan as modulated by climate-induced sediment erosion and deposition. It is uncovered that increased precipitation shifts dominant river erosion patterns from predominantly lateral to headward erosion. A notable outcome is the strong positive correlation identified between drainage density (D_d) and the ratio of crustal shortening rate to rainfall rate (RSR), highlighting the intricate relationship among tectonic activity, hydrology and landscape evolution. In the context of mountain front sedimentation, it demonstrates that material derived from upstream erosional landscape exhibits varying responses to structural and climatic factors. Specifically, bedding patterns are primarily shaped by tectonic forces, whereas climate exerts a controlling influence on particle size distribution. Generally, an acceleration in tectonic deformation rates or a reduction in precipitation rates results in a steeper fan slope. To validate the model's predictive capabilities, select outcomes are compared with natural examples, such as the Longmen Shan, showcasing the high accuracy of the models in replicating real-world scenarios. Overall, this study contributes novel perspective on the intricate mechanism linking tectonic movements, surface processes and climatic fluctuations, enhancing our comprehension of landscape evolution in tectonically active regions with accretionary thrust systems.