Cenozoic Of The Sichuan Basin And The Longmen Shan Denudation

This diploma thesis aims to assess the denudation of Sichuan Basin and Longmen Shan in the eastern margin of Tibetan Plateau, China. It is composed of two parts. The first one is the research about the amount of denudation in Sichuan Basin by using Vitrinite Reflectance technique, and the second one is about the timing of initial denudation in Sichuan Basin and Longmen Shan by using Fission Track Dating technique. This thesis also introduces the applications of Fission Track Dating in thermal history modeling and its laboratory operations. Basing these researches, we have some results below:Analyzing by the Vitrinite Reflectance data of wells located at Sichuan Basin, we find that there is 2-3km thickness of average denudation existing at the basin. The degree of denudation increases gradually from the west to the east, and the thickness distribution is 1-2km at Chengdu Basin, 3-4km to the east of Longquan Shan, and the maximal 5km at some areas.According to the single grain Fission Track ages and the distribution of track length of apatite at Sichuan Basin and Longmen Shan, we have used the HeFTy application software and the anneal model developed by Laselett et al.(1987) to model the thermal history of the samples. The result indicates that, after a mild burial stage, most of the samples undergoes a rapid cooling stage since 30-50Ma B.P. Relating the denudation thickness, we confirm that the average denudation rate is 0.17mm/yr in the basin since Miocene Epoch.According to the single grain Fission Track ages of apatite and zircon in the Longmen Shan, we have calculated the denudation rate at this area by relief-altitude difference way and close temperature way. The result is that Longmen Shan undergoes a rapid denudation process since early Miocene Epoch, and the average denudation rate is 0.72mm/yr.We estimate that the rapid denudation in Sichuan Basin and Longmen Shan since 30-50Ma B.P. is a response to the uplift of Tibetan Plateau, and that, because of the huge difference in the denudation rate between Sichuan Basin and Longmen Shan,...