| Wutai Mountain is located in the north of Shanxi Province and the highest mountain in Taihang Mountain-chain, which is one of the important boundaries of the second and third grade physiognomy in China. The study on its uplifting history is important to confirming the forming age of the three grade physiognomy. In addition, the uplift-exhumation history is basin-mountain coupling with Shanxi rift system, which can help us knowing the revolution of the Shanxi Rift system. The piedmont fault zone of Wutai Mountain, which lies on the north boundary of the Wutai Mountain, is an important boundary active fault in the northern part of Shanxi rift system(also named the Shanxi faulted basin belt or Shanxi graben system). It is the seismogenic fault of the 512 Daixian Ms7? earthquake and the 1683 Yuanping Ms7 earthquake. The quantitative study on its tectonic geomorphology, slip-rates and faulting features, is very important to understanding the active history of the Shanxi rift system in the late Quaternary and it is also of great significance in the earthquake disaster mitigation efforts in the Shanxi Province.In this work, the low-temperature thermochronology method and trench measurement are used to research the tectonic uplift of the Wutai Mountain and the late Quaternary activity of the piedmont fault zone of Wutai Mountain, which is at the scales of million years and thousands of years, respectively. In addition, this thesis also include some work, like field investigations, trench measurement, AMS 14 C dating and OSL dating, GIS technology and so on, which are used to study the activity of the piedmont fault zone of Wutai Mountain in late Quaternary.Million years scale-low temperature chronology method: In this work, I use the apatite fission track method to research the thermal history of dozens of rocks at the Wutaishan area. Combining with previous low-temperature thermochronology data, the fission track data reveal the Cenozoic exhumation process of the rocks and their relations with the activity of the piedmont fault zone of Wutai Mountain. On that basis, the uplift mechanism of the Wutai Mountain and the starting time of the Shanxi rift system are discussed. Apatite fission track ages of the five granite samples, collected from a vertical profile from Beitaiding which is the highest peak of the Wutai Mountain to the foot of the mountain, are range from 64.8 to 80.9Ma, with mean confined track lengths from 11.3 to 13.4?m, and length standard deviations less than 0.84?m. The results show that there exist 2 periods of tectonic uplifts, they occurred in ca. 65-87 Ma and 8±5 Ma, respectively. We also got the average vertical slip rates of the northern piedmont fault of Wutai Mountain is 0.21~1.07mm/a since 8±5 Ma B.C.Ten thousand scale- trench measurement: A test was carried out in the Fanshi section of the northern piedmont fault of the Wutai Mountain, with a small unmanned aerial vehicle. A group of high accuracy point cloud data was produced through Structure from Motion, and then the ortho images, DEM and fine 3D model of fault landform with the resolution of 0.5m was generated after further processing. We analyze the landscapes and calculate the late Quaternary slip rates along the fault zone at the sites in Dayu village and Gangli village, respectively. The vertical slip rates are at least 0.4 mm/a during the last 20 ka and at least 2 earthquakes occurred since about 18 ka. Associated with the analysis of paleo-earthquake events and slip rate, it indicates that the northern piedmont fault of the Wutai Mountain is subject to intensive activity since late Quaternary, especially since Holocene, and there is obvious difference in faulting activity between different segments.The vertical slip rates of the northern piedmont fault of the Wutai Mountain since late Cenozoic and late Quaternary, which are similar, indicate that it has been presenting a steady state since the beginning of the activity. |
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