Landscape and Tectonic Evolution of Bayin River Watershed, Northeastern Qaidam Basin, Northern Tibetan Plateau: Implications for the Role of River Morphology in Source Analysis and Low-Temperature Thermochronology

The Bayin River, the largest river in the northeastern Qaidam basin, plays an important role in the source-to-sink system and landscape evolution at the basin-mountain boundary between the Qilian Mountains and the Qaidam basin in the northern Tibetan Plateau. In this study, we conduct field observation, topographic analysis, zircon U-Pb dating, and apatite (U-Th)/He dating to constrain the landscape and tectonic evolution of the Bayin River watershed. Bedrock zircon U-Pb dating indicates the age group of 420-450 Ma for far-source sediments and the age group of >1,700 Ma for near-source sediments in the Bayin River watershed. Detrital zircon U-Pb dating results from the Mesozoic and Cenozoic strata in the Bayin River watershed reveal that the most important source transition occurred during the Cretaceous. The Zongwulong Mountains gradually uplifted throughout the Cenozoic, along with decreasing far source and increasing near source based on detrital zircon U-Pb dating. Rapid uplift occurred across the Qilian Mountains during the late Cenozoic, leading to high normalized steepness indices, young apatite (U-Th)/He ages, and deep incised valleys at the basin-mountain transition zone. The knickpoints caused by the latest headward erosion just reach an elevation of similar to 3,800 m on the river longitudinal profiles, indicating that the latest uplift magnitude is similar to 300-400 m relative to the basin surface of the Qaidam basin. Elevation distribution and apatite (U-Th)/He ages reveal that river incision leads to high relief in the Zongwulong Mountains and influences its tectonic evolution.