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. Plain Language SummaryThe timing and mechanisms for the high-elevation, low-relief landscape in southeastern Tibet remain at the center of debate. Using apatite fission track and apatite (U-Th)/He thermochronology and thermal modeling, this study sheds new lights on this issue by reconstructing the cooling and exhumation history of the Jianchuan basin, western Yunnan. One major finding is that the Jianchuan basin experienced rapid exhumation during~28-20 Ma at a rate of 0.57-0.80 km/Myr, coinciding with the absence of coeval sedimentation within the basin. Furthermore, morphometric and structural analyses point out a reasonable causal link between production of the topographic relief in the SE Tibet, exhumation of the Jianchuan basin, and thrusting of the Yalong thrust belt. These results allow us to propose a regional-scale tectonic scenario of widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene.

No abstract

We present 24 new apatite fission track (AFT) ages and 18 track length measurements from the Baikal region, SE Siberia. Most samples have AFT ages between 140 and 100 Ma, with relatively high mean track lengths ( c. 13.2 μ m). The relationship between AFT ages, elevation and mean track lengths indicate that the samples record rapid cooling during the Early Cretaceous (140–120 Ma), as also shown by thermal history inversion of track length distributions. Cooling took place during a Late Jurassic-Early Cretaceous orogenic phase, related to closure of the Mongol-Okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting, basin inversion and large vertical motions. The variation in AFT ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role. Minimum amounts of Early Cretaceous denudation are estimated at 2–3 km.