Cenozoic exhumation of the Tianshan as constrained by regional low-temperature thermochronology

The Tianshan range, located in the southern Central Asian Orogenic Belt (CAOB), represents an excellent natural laboratory for investigating intracontinental deformation. The present topography of the Tianshan is closely related to the Indian-Eurasian collision. However, the mechanisms for the topographic development of this range remain debated partly due to the poorly constrained timing of the Cenozoic tectonic events. This study presents the compiled low temperature thermochronological results from 54 studies which include 985 apatite fission track ages, 10 zircon fission track ages, 253 apatite (U-Th-Sm)/He ages, and 49 zircon (U-Th)/He ages to elucidate spatial and temporal exhumation patterns of the Tianshan during the Cenozoic. Based on interpolation of the cooling ages, regional age-elevation relationships, compilation of the thermal modeling results, and spatio-temporal changes in exhumation rates, four exhumation episodes since ca. 60 Ma can be identified, (1) a period of slow exhumation during ca. 60-25 Ma (<0.1 mm/yr) was identified that spanned the entire Tianshan ranges, which suggests limited reactivation and vertical movement in a tectonically stable environment. (2) Moderate (<0.2 mm/yr) with localized rapid exhumation (ca. 0.2-0.3 mm/yr) occurred at ca. 25-15 Ma in the vicinity of major faults in the Tianshan. We interpret this differential exhumation as the indentation of the Pamir and Tarim basin caused by the Indian-Eurasian collision. (3) Widespread thrusting and rapid exhumation (>0.3 mm/yr) occurred throughout the Tianshan ranges in the Late Miocene (ca. 10 Ma), which we interpret as a result of the ongoing of the Indian-Eurasian collision; (4) Rapid exhumation continued from ca. 5 Ma to the present day with localized accelerated exhumation in the southwestern Tianshan, which has been attributed to indentation of the Pamir. Our regional analysis of low temperature thermochronological datasets can provide clear imaging of the exhumation for the entire Tianshan, which effectively constrains the mechanisms of mountain building pro-cesses. Our findings highlight the significant role of tectonics in setting up regional exhumation patterns during the Cenozoic. Moreover, the onset of widespread rapid exhumation in the Tianshan ranges was constrained to the Late Miocene (-10 Ma), and the period of rapid exhumation at the Late Oligocene-Early Miocene (-25-20 Ma) is highly localized at major faults.