Oligocene-Early Miocene Topographic Relief Generation of Southeastern Tibet Triggered by Thrusting

Abstract

The timing and mechanisms of uplift in southeastern Tibet remain disputed. To address this debate, we conducted structural and morphological analyses of the Yulong thrust belt; we also reconstruct the cooling and exhumation history of the Jianchuan basin in the hanging wall of the thrust system using inverse thermal modeling of apatite fission-track and (U-Th)/He thermochronology data. Our results provide evidence for 2.3–3.2 km of rapid exhumation in the Jianchuan basin between ~28 and ~20 Ma, followed by limited exhumation of less than 0.2 km since then. The magnitude of basin exhumation is consistent with the present-day topographic step of 1.8–2.4 km across the Yulong and Chenghai thrust belts, as shown by morphometric analysis. We thus infer that the present-day morphology of the southeastern margin of Tibet results partly from thrusting along the Yulong thrust belt during the Late Oligocene-Early Miocene. This structure may be the southwest continuation of the Longmen Shan thrust belt, offset by the Xianshuihe fault in the Late Miocene. On a regional scale, the approximate synchronicity of exhumation in the hanging walls of the Yalong-Yulong and Longmen Shan thrust systems indicates that widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene.