Bridging the Tianshan-Altai thermochronology gap: a new regional dataset for Central Asia

Abstract

The Central Asian Orogenic Belt encompasses a series of intracontinental mountain belts at the center of the Eurasian landmass, and is widely thought of as a natural laboratory for the study of intracontinental mountain building. Numerous studies have attempted to understand the intracontinental tectonic response of Central Asia to the evolving stress state at the Eurasian plate margins, although much of this work is focussed heavily on the major Tianshan and Altai mountain ranges. As such, the thermal histories of these mountain belts have been extensively studied using a range of thermochronological methods. In contrast, the ~500km wide zone in eastern Kazakhstan and western China that separates the ranges has been relatively neglected, leaving a gap in our understanding of the thermotectonic evolution of Central Asia. In this work, we present a new systematic regional apatite fission track and apatite U-Pb dataset that spans the Chinese West Junggar, Kazakh Tarbagatai, and Dzungarian Alatau ranges, shedding light on the thermal history of this poorly studied region. These data improve our ability to understand the thermo-tectonic history and landscape evolution of Central Asia during the late Paleozoic and Mesozoic. Carboniferous-Permian apatite U-Pb ages were obtained that closely match zircon U-Pb crystallization ages, suggesting fast post-magmatic cooling. Apatite fission track central ages are dominantly Permian to Triassic, with some Jurassic and Cretaceous ages near major faults. Confined fission track length distributions suggest that the rocks that preserve older fission track ages record faster cooling, while the Jurassic and Cretaceous ages are associated with shorter track lengths, which indicate either slower cooling or a more complex mixed thermal history. The dominant trend of the inherited structural framework varies considerably across the region, with large NW-SE striking faults prevalent in eastern Kazakhstan and NE-SW striking faults in the Chinese West Junggar. These faults experienced complex sinistral and dextral strike-slip ductile deformation during the Permian – early Triassic due to plate reorganisation throughout Eurasia at the end of the Paleozoic. Due to the similarity between many of the fission track ages and the timing of regional transcurrent deformation, it is likely that exhumation associated with this event is the explanation for the presence of fast cooling signals at this time. The widespread preservation of these ages suggests that the region has been relatively stable since this Permo-Triassic phase of activity. However, limited post-Triassic brittle reactivation of these structures has influenced the subsequent uplift history of these regions, with variations in fission track age observed across inherited structures.