Northeastward growth of the Tibetan Plateau recorded in the drainage network of the Ordos Loess Plateau

The northeastward expansion of the Tibetan Plateau is caused by the ongoing N–S India-Asia convergence, which leads to the eastward lateral extrusion of fault-bounded blocks. The world-famous Ordos Loess Plateau has an iconic fluvial incision pattern formed on one of these stable cratonic blocks, the Ordos Block. Geomorphologically, the Ordos Loess Plateau on the southern Ordos Block consists of tableland, which relates to the Pliocene Tangxian Planation surface in the western part (Jinghe and North Luohe river areas), and which is more eroded and incised in eastern parts around the Yellow River. In this study, we investigated the effect of tectonic activity on the geomorphic evolution of the Ordos drainage system by field surveys and topographic analysis using digital elevation models. The results show that the drainage systems in the Ordos Loess Plateau are controlled by two factors: (1) the presence of the erosion-resistant fault-bound Weibei Uplift, which represents a barrier separating the southwestern Ordos Loess Plateau from the Weihe Graben; and (2) by the still ongoing surface uplift and erosion due to large increase of the Yellow River catchment since ca. 1.2 Ma. Consequently, the drainage system is in a state of morphological disequilibrium, with drainage basins tilted towards the Liupan Mts. in the west, which overthrusted the western Ordos Block representing a thrust load, which led to tilting of the Tangxian Planation surface. The longitudinal channel profiles of the meandering rivers in the western Ordos Loess Plateau are straight and deviate from usual concave ones because of limited incision due to the fault-bound Weibei Uplift. We suggest that the India-Asia convergence led to the Cenozoic uplift of the Tibetan Plateau and the eastward lateral extrusion of fault-bounded blocks, from which the northernmost was stopped by the cratonic Ordos Block along the Liupan fold-thrust zone. This process led to gentle W-tilting of the southern Ordos Block and is also recorded by GPS data. The formation of unusually straight longitudinal channel profiles is affected by the W-tilting of the Ordos Block and the drainage system reorganized to a principal south-directed flow towards the Weihe Graben in the south. The eastward decreasing elevation of the tableland in front of the Liupan Mts. is related to the indentation of the Liupan Mts. into the Ordos Loess Plateau, which caused the ongoing E–W shortening and ca. N–S extension. Thereby, the eastern Ordos Loess Plateau is progressively incised by and destructed after formation of the Pliocene Tangxian Planation surface. • The cratonic Ordos Block resists the eastward lateral extrusion of the Tibetan Plateau. • The eastward lateral extrusion led to gentle W-tilting of the Ordos Block, which affected the drainage system. • The erosion-resistant Weibei Uplift controls the drainage system and the preservation of the Tangxian Planation surface. • The meandering Jinghe and North Luohe channel profiles are straight deviating from normal ones due to the Weibei Uplift barrier. • The eastern rivers in the southern Ordos Loess Plateau incised deeper and led there to destruction of the Tangxian Planation surface.