New Constraints on the Late Oligocene-Miocene Thermo-Tectonic Evolution of the Southeastern Tibetan Plateau From Low-Temperature Thermochronology

Abstract

The southeastern (SE) Tibetan Plateau (Yunnan) is characterized by low-relief uplands that were deeply incised by large rivers. The thermal history of basement rocks in this region remains poorly investigated, while this data is needed to elucidate the complex relationship between tectonics and climate in shaping the surface. To better understand its thermo-tectonic evolution, we carried out apatite fission track thermochronology on 31 samples collected from a large area that covers different tectonic units, including a vertical profile in the middle Mekong River valley; additional zircon LA-ICP-MS U-Pb dating was performed on four basement rocks. Our results confirm that a large portion of Mesozoic crystalline rocks constitute the basement of the SE Tibetan Plateau. Inverse thermal history modeling of fission track data reveal extensive late Oligocene to Miocene rapid basement cooling and exhumation episodes from both inside and outside the active zones (i.e., ductile shear zone and river valley). These thermal events were coincident with the activities of large-scale strike-slip faults that dominate the structural framework. Combined with the published data, we propose that widespread crustal shortening and thickening took place in the SE Tibetan Plateau during the Oligocene-Miocene in the context of a compressive tectonic regime. Low-temperature thermochronological data reveal that both tectonic forcing and climate-driven erosion have played important roles in exhuming the basement rocks in the region. It is also deduced that the present-day relatively low-elevation landscape of the Yunnan area resulted from complex interaction between regional tectonic activity and surficial erosion since the late Oligocene.