| The Hexi Corridor, located in the northeastern margin of the Tibetan Plateau, is one of regions of most active tectonics and seismic activity. To deepen the study about the tectonic deformation of this region since late Quaternary is important not only for comprehensive recognition of the Tibetan plateau tectonics but also for mitigation of earthquake disaster in this region. Based on summarizing the results of many previous studies before and field work using new offset-landform method, this thesis aims at getting quantitative data about the main active faults in the Hexi Corridor, and then, to interpret quantitatively the cause of the tectonic deformation in the Hexi Corridor by means of vector analysis.1.In order to make up with the insufficiency of the dating data, a chronology of the terraces in the region has been set up by means of analyzing the available data, and comparing with the paloeclimatic history revealed by high-resolution records from the ice-core, loess-paleo-soil series, plateau lakes and strata of desert. "Forming periods", i.e. periods when terraces tend to form responding to worm and humid climatic condition, is proposed to constrain the ages of the terraces. Five forming periods are recognized in this region: Period A, 4.2 ± 1.0 (3-5) ka BP; Period B, Period 8.0±2.0 (6-10) kaBP; C, Period 12.8± 1.5 (12-14) ka BP; Period D, 22.8±2.0 (20-24) ka BP and Period E, 30±2.0 (28-32) ka BP.2. The active faults in the Hexi Corridor can be classified into 4 types according to their tectonic positions, histories, kinematics, and trending directions. The first type is the boundary faults of the Hexi Corridor foreland basin (including the northern Qilianshan fault belt, the southern Longshoushan fault zone and the northern Longshoushan fault), which undergo long geological evolution, orientate NWW in accord with the direction of regional main tectonic line, thrust to the Hexi Corridor foreland basin, and form sharp contrastive landforms. The second type is the reverse fault system interior the Hexi Corridor basin, which is related with NNW-trending tectonic uplifts in the the Hexi Corridor basin, and includes 6 faults (the Jiayuguan fault, Yingwanshan fault, the northern Yumushan fault, eastern Yumushan fault, the Huangcheng-Taerzhuang fault, and the southern Wuwei basin fault). The faulting of the system and the rising of the NNW-trening tectonic uplifts divides the Hexi Corridor basin into 4 sendonary basins (Jiuxi basin, Jiudong basin, Minle basin, and Wuwei basin). The third type is southern Alashan EW-trending strike-slip fault belt. It containes 5 faults and splits eastward. Each fault controls basins in the shouthem margin of the Alashan block and is featured by lateral strike-slip since the late Quaternary. The last type is the NWW-trending faults system in the north Qilianshan mountains. The faults appear along margins of mside-montain basins and are featured by reverse-strike slips. These 4 types of structures constitute the basic tectonic framework of the Hexi Corridor. Summarizing previous studies and fieldwork yield the slip rates of the faults, which are described below: (1)Among the northern Qilianshan fault zone, the vertical slip rates of the Yumen fault and the Fudongmiao-Hongyazi fault are 0.74-1.24mm/a and 0.56 mm/a, respectively since the Mid-Pleistocene, while the Hanxia-Dahuanggou fault and the Minle-Damaying fault are inactive since the Holocene. (2)The inner reverse faults include the Jiayuguan fault, Yingwanshan fault, the northern Yumushan fault, eastern Yumushan fault, the Huangcheng-Taerzhuang fault, and the southern Wuwei basin fault. The vertical slip-rates of them are 0.53 mm/a. 0.18 mm/a, 1.0 mm/a, 0.3 mm/a (southeastern part), 0.54-0.8 mm/a, 0.57 mm/a, respectively. (3) The southern Alashan EW-trending strike-slip fault belt contains 5 faults, i.e., Jintananshan fault, Mushaoliangfault, Pantoushan-Yangjuangou fault, Tiancheng-Suhaiamu fault, and Ayouqi fault. The slip-rates of them are 1.9+0.7 mm/a, 0.5 mm/a, 0.5 mm/a, 1.3+0.2mm/a,...
|
PDF Full Text Request