Horizontal differentiation of crustal rheology control the deformation of Haraarat thrust belt : insight from numerical modelling

The rheological structure of the lithosphere is an essential factor controlling continental collision. The structural deformation and topography of the Haraarat Thrust Belt are pretty different from those of the thrust belts around the Tibet Plateau, indicating that a crustal rheology study is needed. In this paper, we conducted seven single-factor experiments using two-dimensional numerical simulation to explore the horizontal differentiation of the upper crust strength beneath the basin and the mountain. The results show that: the structural deformation would concentrate on orogen if the upper crust strength is in the 'weak orogen and strong basin' pattern, and the vertical superposition of fault blocks would cause the orogen uplift, leaving structural highs of the topography developed mainly in the orogenic belt. The structural deformation would concentrate in both basin and thrust belts if the upper crust strength is in `strong orogen and weak basin' pattern, and the structural highs mainly appeared in the thrust belt instead of the hinterland owing to the orogen-basin interaction. Based on these single-factor experiments, we simulate the tectonic evolution of the Haraarat Thrust Belt and found that after the development of the nappe structure in the Late Permian, the tectonic deformation weakened gradually in the Haraarat Thrust Belt, where the propagating mode changed from forward to backward, and the basement dip reversed from hinterland to foreland. Combined with the geophysical data of the Haraarat and Longmenshan thrust belts, we found that the structural deformation and topography of the Haraarat Thrust Belt and the Longmenshan Thrust Belt conform to the 'strong mountain and weak basin' and the 'weak mountain and strong basin' patterns, respectively. These results could provide important insights into establishing geodynamic and experimental models of thrust belts in Central-Western China and have guiding significance for reservoir-controlling analysis and oil -gas exploration in the study area.