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

Abstract

Understanding the role of southeastern Tibet thrust faults in the development of the plateau topography is key to our assessment of the geodynamic processes shaping the continental topography. Detailed structure analysis along the ~400 km long Jinhe-Qinghe thrust belt (JQTB) indicates post late Eocene thrust motion with a minor left-lateral component, inducing ~0.6 to 3.6 km of apparent vertical offset across the fault. The exhumation history of the Baishagou granite, based on the thermal modeling (QTQT) of new apatite (U-Th)/He and fission-track ages, suggests an accelerated exhumation rate (~0.42 km/Myr) between 20 and 15 Ma, corresponding to ~1.7-2.4 km of exhumation. We interpret that fast exhumation as due to the activation of the Nibi thrust, a northern branch of the JQTB resulting in the creation of significant relief across the JQTB in the Early Miocene. 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, coevally with Indochina extrusion, the second thrusting phase occurred along the Yulong and Longmenshan thrust belts, and then migrated to the JQTB at 20-15 Ma. A third phase involved the activation of the Xianshuihe fault and the re-activation of the Longmenshan thrust belt and the Muli thrust. Uplift in the hanging wall of thrust belts appears to explain most of the present-day relief in the southeastern Tibetan Plateau.