Drainage-divide migration at the Qinling and its implications for the drainage reorganization and rift evolution of the Weihe graben, Central China

Abstract

The east-trending Qinling horst and Weihe graben system in Central China is an important tectonic transition zone between the transpressional Northeastern Tibetan Plateau and the transtensional Eastern North China Craton. However, it remains unclear how the horst-graben system and the modern drainage morphology have evolved in this region. Here we analyze the stability of the main drainage divide at the Qinling, based on χ-plot and Gilbert metrics, and estimate the divide migration rates using the catchment erosion rates from cosmogenic nuclide ¹⁰Be data. Our results show that the drainage divide in the western part of the Qinling is moving southward, while that in the eastern part is mostly stable. We suggest that the migration of the Qinling drainage divide is controlled by the subsidence of the Weihe graben, and the along-strike variation in the drainage-divide stability results from the westward expansion of the Weihe graben. Moreover, based on the wind gaps, barbed tributaries, Holocene sediment close to the wind gaps, and landscape numerical modeling results, we identify two major river capture events near the rift-bounding normal fault, likely caused by both the subsidence of the Weihe graben and the uplift of the Qinling horst in the Cenozoic. The results indicate that before the capture events, some rivers in the southern Ordos used to flow southward across the Qinling into the Sichuan Basin, which is of great significance to the evolution of the middle Yellow River.