Multi-stage differential exhumation of the West Junggar and adjacent regions, NW China, revealed by regional low-temperature thermochronology

The West Junggar, a key segment of the Central Asian Orogenic Belt, lies between the ranges of the Tianshan and Altai Orogenic Belts, providing an opportunity to investigate the complexities of an orogenic system that records long-term intracontinental deformation. Although the West Junggar Orogenic Belt has been reactivated multiple times since the late Paleozoic, the timing and driving forces behind these events remain poorly constrained. Additionally, the different response mechanisms to specific tectonic events of the West Junggar, Tianshan, and Chinese Altai orogenic belts have not been thoroughly explored. To address these questions, we present new zircon and apatite (UTh)/He and apatite fission track data, combined with a synthesis of previously published data, including 1080 apatite fission track ages, 28 zircon fission track ages, 302 apatite (UTh)/He ages, and 68 zircon (UTh)/He ages. These data allow us to reconstruct the spatial and temporal exhumation patterns of the West Junggar and adjacent regions since the late Paleozoic. Our results reveal two cooling phases of the West Junggar Orogenic Belt: rapid cooling during the early Permian to late Triassic (∼290–230 Ma), associated with the closure of Paleo-Asian Ocean, and moderate cooling during early Jurassic to early Cretaceous (∼180–140 Ma), driven by strike-slip fault reactivation related to the counterclockwise rotation of Junggar Block. Orogen-scale contour maps of low-temperature thermochronological ages and exhumation rates highlight contrasting deformation patterns across the Tianshan, Chinese Altai, and West Junggar Orogenic Belts. The Tianshan Orogenic Belt underwent multiple stages of cooling and exhumation, where large strike-slip fault systems and preexisting crustal heterogeneities led to an irregular spatiotemporal distribution of deformation in the Mesozoic and Cenozoic. The most extensive and intense deformation occurred in the late Miocene, likely associated with the India-Eurasia collision. However, owing to a lithospheric weak zone beneath the Tianshan Orogenic Belt, far-field stress associated with this collision was insufficient to drive Cenozoic deformation in the Chinese Altai Orogenic Belt. A regional pulse of Cretaceous cooling is recorded throughout the Chinese Altai, though the tectonic driver remains debated. In contrast, the West Junggar has remained remarkably stable since the late Mesozoic. Based on the regional geological structure, we propose that the stability of the West Junggar since the late Mesozoic can attributed to two factors: the NE-SW structure is consistent with the maximum principal stress orientation, and the rigid Kazakhstan Orocline, which has likely inhibited significant shortening or reactivation in the region.