Asynchronous uplift of the South and Central Tian Shan in the Mesozoic: Insights from detrital zircon geochronology on the Southern Tian Shan Foreland Basin (NW China)

The Tian Shan orogenic belt, Earth's largest active intracontinental mountain belt, has experienced multiple reactivation and uplift events since its late Paleozoic amalgamation. However, the mechanisms driving these processes, as well as the relative uplift timing and rates of its secondary tectonic units, such as the South Tian Shan (STS) and Yili Block-Central Tian Shan (Yili-CTS), remain unclear. To investigate these issues, we analyzed detrital zircon UPb isotopic ages and heavy mineral assemblages from late Paleozoic to Cenozoic sedimentary rocks in the Southern Tian Shan Foreland Basin (STFB) using deep drilling samples. Our results document distinct detrital zircon responses to three major reactivation events during the Mesozoic–Cenozoic. In the late Triassic, detritus from the Yili-CTS first reached the STFB, likely due to enhanced erosion linked to a megamonsoon. By the early Cretaceous, the Yili-CTS had become a dominant sediment source, although its contribution declined in younger formations, indicating a delayed uplift of the STS relative to the Yili-CTS. These observations suggest that the Mongol-Okhotsk orogeny might trigger the early Cretaceous uplift of the Yili-CTS, with subsequent remote effects from the Lhasa–Qiangtang collision driving the STS’s uplift. Since the late Paleogene, uplift and shortening have been concentrated along the mountain front thrust-fold belts, blocking sediment transport from the Yili-CTS to the STFB, while tectonic quiescence in earlier periods allowed for increased contributions of the Yili-CTS-derived sediments, reflecting the overall planation of the Tian Shan. These findings provide new insights into the topographic evolution of the Tian Shan during multiple phases of intracontinental orogenesis and highlight the interactions between regional tectonics and far-field geodynamic forces.