Mesozoic building of the Eastern Tianshan and East Junggar (NW China) revealed by low-temperature thermochronology

Abstract

The Eastern Tianshan and East Junggar orogenic belts are major constituents of the southwestern Central Asian Orogenic Belt. This study applies low-temperature thermochronology to constrain the thermo-tectonic history of these two domains. Apatite fission track (AFT) dating of Paleozoic basement samples from the Eastern Tianshan and East Junggar dominantly yield Cretaceous (∼126–70 Ma) AFT ages, except for two granitic samples from the East Junggar with older ages of ∼239 and ∼157 Ma, respectively. Thermal history modeling reveals that the Eastern Tianshan and southern part of the East Junggar experienced moderate to rapid basement cooling throughout the Cretaceous. We interpret it as a far-field effect of accretion and collision along the south Eurasia margin since the Early Cretaceous. Major faults were reactivated and thus may have played an important role in controlling localized fast uplift and cooling. We also dated seven Mesozoic sandstone samples collected from the eastern margin of the Junggar Basin. The detrital AFT age peaks, together with inverse thermal history modeling of the basement, reveal that the East Junggar underwent late Permian to Early Jurassic cooling episodes. These cooling events are thought to be related to post-orogenic transpression along major faults and distal effect of Qiangtang-Eurasia collision. Combined with already published evidence, our new data suggest that the Eastern Tianshan and East Junggar did not undergo significant exhumation during the Cenozoic.