Abstract:

This paper characterized the spatio-temporal differences in rock rapid cooling events during the Meso-Cenozoic through frequency analysis and phased interpolation based on systematically collected apatite fission track ages, U-Th/He ages, and fission track length data from the Tianshan Mountains and northern Central Asia. And it also discussed the relationship between rock rapid cooling events and the dynamics of plate boundaries by considering tectonic deformation in different regions across various stages. The results indicate that the Tianshan Mountains experienced four primary rapid cooling events, which occurred in the Late Triassic, Late Jurassic-Early Cretaceous, Late Cretaceous-Paleogene, and Middle-Late Cenozoic periods. The rapid cooling event in the Late Triassic, mainly observed in the western segment of the Tianshan, is linked to rock uplift and exhumation resulting from reverse thrusting, potentially controlled by the collision between the western Turan block and the paleo-Asian continent. During the Late Jurassic-Early Cretaceous, rapid cooling was primarily found in the western Kyrgyz Tianshan and the easternmost Tianshan, where both events were associated with thrusting-controlled rock uplift and exhumation. The uplift in the western Kyrgyz Tianshan is probably connected to the far-field effects of the collision between the southern Lhasa block and the paleo-Asian continent, while uplift in the easternmost Tianshan was likely influenced by the far-field effects of the closure of the northern Mongol-Okhotsk Ocean. The rapid cooling event during the Late Cretaceous-Paleogene is primarily characterized by thermal cooling along major faults. In the western Kyrgyz Tianshan, western Chinese Tianshan, and the Jueluotage region in the southern part of the eastern Tianshan, this rapid cooling due to faulting mainly occurred in the latest Cretaceous-Paleogene and can be attributed to the accretion of island arcs such as Kohistan-Dras, as well as the final collision between the Indian and Eurasian plates. But in the Harlik Mountains, located in the northern part of the Eastern Tianshan, this rapid cooling mainly happened in the middle Late Cretaceous, slightly earlier than in other regions but was synchronised with the post-collision extensional collapse of the northern Mongolia-Okhotsk orogenic belt. The faulting associated with this rapid cooling in the Harlik Mountains demonstrates a dextral transtensional movement within a northeast-southwest tensile stress field, suggesting a dynamic link between the dextral transtension in the Harlik Mountains and the post-collision collapse in the northern Mongolia-Okhotsk orogenic belt. The strong uplift and exhumation event in the mid to late Cenozoic is mainly observed in the Pamir and the western segment of the Tianshan, reflecting the far-field effects of intense intracontinental compression caused by the rise of the Tibetan Plateau and its northward expansion following the collision between the Indian and Eurasian plates. In summary, the rapid cooling events in various parts of the Tianshan Mountains during different stages of the Meso-Cenozoic era were the result of the combined effects of various plate boundary dynamics, including multi-block collisions and the subsequent rise of the Tibetan Plateau in the southern Tethys tectonic domain, as well as the closure of the Mongol-Okhotsk Ocean and the resulting post-collision extensional collapse in the northern tectonic domain.

Key words: Tianshan Mountains, Meso-Cenozoic, low-temperature thermochronology, rock rapid cooling event, far-field effect