Interplay of the sinistral Altyn Tagh fault and the Qilian Shan thrust system along the northeastern margin of the Tibetan Plateau: Insight from the Hongliuxia bend

The Cenozoic northeastern margin of the Tibetan Plateau, where the left-lateral Altyn Tagh fault (ATF) interacts with the Qilian Shan thrust system, is a critical zone for understanding outward plateau growth. We investigated the Hongliuxia bend, an overlap region between the easternmost ATF and the northward-propagating Qilian Shan front, through structural and stratigraphic investigations, geomorphological analyses, and luminescence dating. Three fault systems were identified: (1) an E–W-striking left-lateral fault (F1) along the core of the Hongliuxia anticline, accommodating a slip rate of ~0.8–1.3 mm/yr, comparable to that of the nearby ATF; (2) a NEE–striking fault (F4), which likely initiated prior to ca. 1.2 Ma and merges downward into fault F1 to form a positive flower structure; and (3) NW-striking thrust faults (F2 and F3), truncating the southern limb of the Hongliuxia anticline, which were active after ca. 130 ka and likely represent part of the North Qilian Shan thrust front. Reinterpreted geophysical profiles reveal that fault F1 aligns with a steep crustal boundary between the Jiuquan Basin and Gobi–Alax Block, whereas the easternmost ATF lacks such a deep geophysical signature. These observations suggest that the ATF terminates at the Hongliuxia bend, with its strike-slip strain largely absorbed by fault F1. Our results further reveal clear structural superposition between the ATF’s strike-slip and the Qilian Shan’s thrusting domains, providing a potential mechanism for the arcuate fault system in the western Qilian Shan, through stepwise strike-slip termination and elongation of the ATF, overprinted by synchronous northeastward propagation of the Qilian Shan thrust front. This kinematic interaction serves as an analog illustrating how major intracontinental strike-slip faults partition strain and interplay with regional thrusts at their distal terminations.