Spatio-temporal Pattern of Exhumation over the Tibetan Plateau During the Cenozoic: A Review from the Perspective of Thermochronology

Abstract:

Rise and subsequent erosion of the Tibetan Plateau have long been hotspots in the geoscience world. Whilst numerous thermochronological studies have been conducted to reveal the bedrock exhumation in and around the Tibetan Plateau, the spatio-temporal pattern of the exhumation over the entire Tibetan Plateau during the Cenozoic era remains unclear. Herein, we summarized published low-temperature thermochronological (including apatite fission track and (U-Th)/He, and zircon (U-Th)/He) results that have been well constrained by elevation profiles in the Tibetan Plateau and the Tian Shan. We compared the onset ages of accelerated exhumation of different orogenic belts in the Tibetan Plateau, and calculated the exhumation rates over the entire plateau during different periods of the Cenozoic era. Two preliminary conclusions were drawn. (1) The onset of accelerated exhumation was ~40 Ma or even older in the interior of the Tibetan Plateau (such as East Kunlun Shan), but changed to <20 Ma in the plateau margins (e.g., 17 – 12 Ma in the central and south Qilian Shan, 12 – 8 Ma in the north Qilian Shan, 17 – 5 Ma in the Tian Shan, and 20 – 2 Ma in the SE Tibetan Plateau). The corresponding onset ages in the Himalaya and Pamir regions were not revealed by published results but should be no later than middle Miocene. If the accelerated exhumation was caused by tectonic loading in response to India – Eurasian collision, this spatial pattern implied a phase of rapid outward growth of the Tibetan Plateau in the Early Miocene. (2) Although bedrock exhumation rates vary in time and space, very fast rates (>1 mm/a) only occurred since ~20 – 15 Ma, which is consistent with the Middle Miocene Climate Optimum in ~17 – 14 Ma, and in the SE Tibetan Plateau, Himalaya and southern Pamir that are impacted by Asian Monsoon system. These coincidences suggest that climate has played an important role in enhancing the bedrock erosion in the plateau margins since the Early Miocene.