Detrital zircon provenance constraints on the initial uplift and denudation of the Chinese western Tianshan after the assembly of the southwestern Central Asian Orogenic Belt

- Sediment provenance shifted abruptly in the mid-Triassic in the northern Tarim basin.
- The provenance shift reflects the first-phase intense uplift of the Tianshan range.
- The uplifting event resulted from the far-field effects of Qiangtang-Tarim collision.

U-Pb and Lu-Hf isotopic data of detrital zircons from late Paleozoic and Mesozoic strata along the southern flank of the Chinese western Tianshan enable to identify provenance changes and reconstruct early stage uplift and denudation history of the Tianshan range. Detrital zircons from Permian and Early-Middle Triassic siliciclastic rocks show two prominent age populations at 500-390 Ma and 310-260 Ma, and subordinate Precambrian ages at ~ 2.5 Ga, 2.0-1.7 Ga, 1.2-0.9 Ga and 900-600 Ma, with rare ages between 390 and 310 Ma. These characteristics and zircon εHf(t) data consistently suggest a sediment source predominantly from the Tarim Craton, rather than the Central Tianshan-Yili Block. In contrast, Late Triassic to Cretaceous strata additionally contain abundant 390-310 Ma and 260-220 Ma detrital zircons, implying multiple source regions from the Central Tianshan-Yili Block, Tarim Craton, and Western Kunlun Orogen. A significant switch of sedimentary provenances occurred in the mid-Triassic and is consistent with contemporaneous change of paleocurrent directions and the onset of intense tectonothermal events in the broad region of the Chinese western Tianshan and Kyrgyz Tianshan. These data collectively indicate that the significant surface uplift and denudation of the Tianshan range were probably initiated in the mid-Triassic (~ 240 Ma) after the assembly of the southwestern Central Asian Orogenic Belt. This uplifting event represents an intracontinental orogeny most likely in response to the collision between the Qiangtang Block and southern Eurasia, following the closure of the western part of the Paleo-Tethys Ocean.