Geodynamics of progressive growth of arcuate fold-and-thrust belts: Insights from numerical modeling of the NE margin of the Qinghai-Tibetan plateau

Abstract

As the front of the northeastward-growth region of the Qinghai-Tibetan Plateau since the Cenozoic, arcuate fold-and-thrust belts are the main features of local tectonic deformation. However, the formation mechanism of these arcuate structures is still an open question. We present 3D finite-element models with elasto-plastic rheology to understand the formation-evolution of arcuate folds here comprising real regional fault-zones including the Haiyuan, Xiang Shan–Tianjing Shan, Yantong Shan, and Niushou Shan faults since ∼10 Ma. The reference-model equivalent-plastic-strain (EPS) concentration zones develop outwardly-NE in spatio-temporal sequence, with development geometry and timing in good agreement with the geologic fault-zone structures. Our reference-model-based sensitivity analysis suggest that the horizontal northeastward compression of the region being bounded by a frictional vicinity (rigid Alxa and Ordos blocks hindering the advancement) have the dominant control on the formation and evolution of these arcuate fold-and-thrust belts perpendicular to the contraction axis. In contrast, the likely-small rotations imprinted by the Ordos and Alxa blocks and the minor shearing of the Qinghai–Tibetan Plateau, have only secondary effects. An additional, generic sensitivity analysis reveals that the folds’ horizontal curvature per unit horizontal shortening-displacement increases with the friction on the bounding vicinity, and this result could be considered for other scenarios of Earth and other planets. Historical regional earthquakes of M > 6 are mostly located in the simulated EPS concentration zones: the 1920 Haiyuan and 1709 Zhongwei earthquakes occurred on the Haiyuan and Xiang Shan–Tianjing Shan faults, respectively, well correlated with our model high-EPS concentration zones.