Diachronous Growth of the Altyn Tagh Mountains: Constraints on Propagation of the Northern Tibetan Margin From (U-Th)/He Dating

The sinistral Altyn Tagh strike-slip fault demarcates the northern boundary of the Qinghai-Tibetan Plateau; however, the significance and timing of activity along the fault are debated. Here new apatite and zircon (U-Th)/He data are presented, revealing the exhumation history of the Altyn Tagh Mountains from crustal depths of similar to 2-7km. Studies of rock samples from the Altun Shan region show that they were located close to the surface during the Early Cretaceous and remained so until about 40Ma. Samples from the Subei and Dangjin Pass areas, on the other hand, record a period of rapid exhumation at 202Ma, and samples from the Qiemo area record a period of continuous exhumation between similar to 20 and 12Ma at a rate of 0.046-0.013+0.007year, plus a further rapid cooling event at 7-5.5Ma. Thus, significantly more exhumation has occurred toward the southwestern section of the Altyn Tagh Fault Zone, indicating a decrease in tectonic uplift toward the northeast since the Miocene. During the late Miocene, the Tarim Block began to subduct beneath the northern Tibetan margin, resulting in rapid exhumation of the central section of the Altyn Tagh Fault Zone. In accordance with previous studies, the present results support a model of northward propagation and expansion of the Qinghai-Tibetan Plateau during the Cenozoic.