Climatic aridification restrained late Cenozoic denudation of the Tian Shan in the inland of Asia

Quantifying erosion rates over various temporal and spatial scales is the key to understanding the respective roles of tectonic and climatic factors in driving the topographic evolution of an active orogenic belt. This work focuses on the spatiotemporal patterns of denudation rate in the Tian Shan and its implication for topographic evolution by utilizing low-temperature thermochronological analyses. Apatite (U-Th)/He thermochronological analyses and thermal history modelling were conducted on eight samples taken from a ∼ 0.7-km elevation transect at the glaciated headwaters of the Urumqi River in the northern Chinese Tian Shan. The results reveal dominant Mesozoic thermochronological ages and limited Cenozoic exhumation, although the sampled area was subjected to intensive glaciation at least during the late Quaternary. The restrained late Cenozoic exhumation at the glaciated Urumqi catchment is also revealed in the other parts of Tian Shan. The inversion of ∼1780 published thermochronological ages shows that, although the exhumation in the Tian Shan has been enhanced since the late Oligocene due to tectonic rejuvenation and pulsed uplift of the range, the long-term exhumation rates in most of the Tian Shan are generally < 0.2 km/Myr, obviously lower than that in some other active orogenic belts characterized by a more humid climate. Given the fact that the late Cenozoic climate in the Tian Shan was characterized by stepwise aridification due to uplifting topographic barrier of the range for the Westerlies, we propose that climate aridification beginning since the late Oligocene could have acted as the equalizer of range-scale denudation, thus restraining the late Cenozoic denudation of the Tian Shan, a typical reactivated orogen belt in the arid inland of Asia.