Tectonic Geomorphology Of The Qinling-Daba Mountains And Its Geodynamic Implications

The formation and growth of the Tibetan Plateau,as well as the complex intracontinental structures and deep processes resulting from the collision and convergence of continents,have been one of the most important issues in solid earth science.The Qinling-Daba Mountains are located at the frontal part of the northeastward and eastward growth of the Tibetan Plateau,the tectonic deformation and landscape evolution are windows to detect the continental dynamics of the expansion of the Tibetan Plateau.Compared with the northern and southern borders of the Tibetan Plateau,the current landforms of the Qinling-Daba Mountains are characterized by dispersion and irregularity.It has limited our understanding about the northeastward growth of the Tibetan Plateau.However,the landforms and drainage systems are geological records of the plateau expansion at shallow crust in this area,they are also the link between the deep geological processes and the earth surface process.In this thesis,we aim to detect the drainage systems evolution in the Qinling-Daba Mountains,thus,the longitudinal profile and quantitative tectonic geomorphic parameters in typical areas were studied,such as the Upper Jiangling River Basin and Upper Weihe River Basin in the West Qinling Mountains,Heihe River Basin in northern margin of Qinling Mountains,Taibai Fault,and many small drainage systems in Daba Mountains.The main conclusions and understanding of this thesis are as follows:(1)The longitudinal profile analysis suggested that the landscape evolution of the Upper Jialing River Basin in the West Qinling area is in a transient state.Local comparisons of the knickpoint development and channel steepness revealed that the lithology and precipitation have limited influence on the knickpoint development and channel steepness.The knickpoint development and the variation of channel steepness were controlled by the base-level fall that was caused by the tectonic uplift.The spatial patterns of normalized channel steepness revealed that the tectonic force plays a significant role in shaping the landscape.(2)The longitudinal profile analysis indicated that the landscape evolution of the Upper Weihe River Basin is in a transient state as well.The evolution of the longitudinal profile was controlled by the base-level fall that was caused by the tectonic force.The distribution of the knickpoint showed that the Upper Weihe River Basin has an overall but different rock uplift,the West Qinling Mountains and the south Liupan Shan areas have a high uplift rate.Reconstruction of the paleochannel indicates that the upper Weihe River has an average incision of 354 ± 130 m since late Early Pleistocene and the south tributaries has a higher incision of 144 ± 25 m than the north.An average river erosion rate of 0.25-0.3 m/ka was estimated,the West Qinling Mountains has a higher erosion rate of 0.1-0.12 m/ka than Longzhong Basin and the south Liupan Shan.(3)The quantitative tectonic geomorphic parameters revealed that the formation of the upstream landscape of the Heihe River Basin takes a long time,it represents the topography that was flattened before the Qinling Mountains were uplifted.However,the downstream landscape of the Heihe River Basin is relatively young,it is the new landform that was formed by the extensional uplift of the Qinling Mountains.The crustal extension and isostasy controlled the uplift of the Qinling Mountains.Meanwhile,the outward expanding stress of the Tibetan Plateau has acted on the Qinling Mountains through the Taibai Fault and accelerated the uplift of the Qinling Mountains.(4)Relative active tectonics assessment and longitudinal profile analysis indicate that the Daba Mountains can be divided into three tectonic deformation zones,from west to east,they are compressional deformation zone,strike-slip deformation zone and vertical uplift zone.Deformation style changed from shortening to strike-slip as the distance gets longer from the Tibetan Plateau.When tectonic stress reached Huangling massif,which is a rigid block,the vertical uplift dominated the crustal deformation.Base on above,we inferred that the eastward expansion of the Tibetan Plateau has controlled the late Cenozoic tectonic deformation and shaped the modern landscape of the Daba Mountains.(5)The Qinling-Daba Mountains have different deformation mechanisms in different regions.In the West Qinling and north margin of Qinling Mountains,the tectonic deformation is primarily controlled by the continental extrusion.But in the Daba Shan area,the crustal deformation is likely associated with the deformation and thickening in the deep crust.