An Integrated Study On Late Cenozoic Tectonic Deformation In The Liupanshan-Madongshan Area, Northeastern Margin Of The Tibetan Plateau

The northeastern margin of the Tibetan plateau is the frontier of the northeastward expanding Tibetan plateau since the late Cenozoic. This region is characterized by a structural pattern of"basin and range"which was formed during the uplifting and outward expanding process of the Tibetan plateau in the late Cenozoic era. Mountains controlled by fold and thrust belts uplift strongly, and separate the widespread Cenozoic basin into many smaller basins with thick Cenozoic deposits. The Cenozoic stratum of the northeastern Tibetan Plateau is spectacular, distributed from the Liupanshan, via the Hexi corridor, Qilianshan and Qaidam, to the Tianshan. Since the Oligocene all these areas are characterized by thick, nearly continually deposited layers. The Cenozoic layers not only record the environment change, but preserve detailed information about the Cenozoic tectonic deformation also. Therefore, the northeastern Tibetan Plateau is an ideal region for the resolution of problems, such as the uplifting history of the Tibetan Plateau.The Liupanshan-Madongshan, which is located on the eastern segment of the Haiyuan fault zone is a typical Mesozoic and Cenozoic compressive thrust mountain belt. The correlative sedimentary and orogenic evolvement have the character of continous deformation and periodic pulsatory mountain-building in the basin-and-range coupling system,To the north, the Sikouzi basin is a typical foreland basin and the trailing-edge Longde bansin is a representative basin with thrusting and strike-slipping since the Miocene. The development of these basins is coupled with the uplifting of the surrounding mountains. The basins are filled with thick terrigenous deposits which record detailed information about the uplifting of the Tibetan plateau, intracontinental collision and relevant Cenozoic deformation. Deciphering of these records will help illuminate the history of Cenozoic deformation, migration of deformation, relationships among different structures, and the histories of deformation and uplifting of the whole northeastern margin of the Tibetan plateau.Based on integrated analyses of the regional geologic setting, depositional characteristics, paleomagneto-stratigraphy, bio-stratigraphy, sedimentary facies, tectonic sequences, and sequences and styles of the Cenozoic deformation, many interesting results are obtained, and the evolution process of the mountains and basins of the studied region are discussed. Main results of this thesis are summarized below:Different types of basins developed in the front of and behind the Liupanshan-Mandongshan fold and thrust mountain belt. The Sikouzi basin in front of the mountain is a typical foreland basin, while the Longde basin, which lies at the back of the Liupanshan, is a compressive, strike-slip related basin.The Sikouzi section is emphasized in this study. Along this section systematic paleo-magnetic samples are collected and analyzed. The results show that most of the layers were deposited since the Miocene. According to the paleomagnetic ages, formations on this section are divided and calibrated, and six formations are recognized. The lowest Sikouzi formation is the early Miocene(N₁¹)with the bottom age of 18.02 Ma, and there is a 1.53Ma disruption of the deposition...