Role of the Early Miocene Jinhe-Qinghe Thrust Belt in the building of the Southeastern Tibetan Plateau topography

Understanding the development of key thrust faults in southeastern Tibet is significant to reconstructing the geodynamic and topographic processes. Detailed structure analysis along the ~400 km long Jinhe-Qinghe thrust belt (JQTB) indicate thrust motion with a minor left-lateral component. The exhumation history of the Baishagou granite, based on apatite (U-Th)/He and fission-track thermochronology and thermal modeling, suggest an accelerated exhumation rate (~0.42 km/Myr) between 20 and 15 Ma. We interpret that fast exhumation due to the activation of the Nibi thrust, a northern branch of the JQTB. The ~1.5-2.2 km of exhumation that occurred corresponds to the present topographic difference across the thrust belt. In the Early Miocene, significant relief along JQTB was generated by thrusting. When compared with previous studies it appears that Cenozoic exhumation and relief creation in southeastern Tibet cannot be explained by a single mechanism. Rather, at least three stages of relief creation should be invoked. The first phase is an Eocene NE-SW compression partly coeval with Eocene sedimentation. During the Late Oligocene to Early Miocene the second thrusting phase occurred along the Yulong and Longmenshan thrust belts, and then migrated to the JQTB further to the southeast during 20-15 Ma. A third phase involved the activation of the Xianshuihe fault and the re-activation of the Longmenshan thrust belts and the Muli thrust. The interaction between thrusting and fast river erosion triggered by climate change is not certain but thrusting along thrust belts appears to explain most of the present-day relief in the southeastern Tibetan Plateau.