Features Of Lanping-Simao Foreland Basin Of Jurassic And Cretaceous Period In Southern Yunnan And The Discussion Of Mountain-Basin Coupling

Being one constituent part of the Tethyan-Himalayan orogenic belt, Lanping-Simao basin is located between the Lancangjiang fault and the Ailaoshan fault, with its northern part called Lanping basin and southern part called Simao basin (Puer Basin). It is located in the southern part of Sanjiang fold system and is a relatively large sedimentary basin of the Meso-Cenozoic period. The variable crustal structure and advantageous geographic location here has important value of theory and practical significance for further study of the formation and evolution of the Tethys ocean, the uplift process of the Qinghai-Tibet Plateau, the prediction of metallogenic regularity as well as the search of oil-gas reservoir.Firstly, this thesis will introduce the geological background in the basin area, including the tectonic geology, regional stratigraphy, magmatic activity and the tectonic framework, so as to get hold of the overall information of the basin from the eastern margin to the western margin. Secondly, we will study on the Cretaceous and Jurassic strata though field measured section. Through lithology analysis and contrasts, depositional environment and sedimentary facies analysis, the filled characteristics of strata and the vertical distribution of the depositional systems within the basin will be explained, thus to determine the nature of the basin. Thirdly, the structural features of the eastern margin and western margin of the basin will be studied. Finally, mountain-basin coupling in the eastern margin of the basin will be discussed and though Thermochronological dating, the uplift history of the basin will be obtained.Though both the field geological investigation and the indoor materials arrangement, we can arrive at that the researched region is within the Tethys structural domains, which is between the Gondwana land and Laurisia land. There are two first-level tectonic units in this area, the yangtze paraplatform and the Tanggula-Changdu-Lanping-Simao fold system, formed though long-lived and continuous mutual geological process. Lanping-Simao basin is located between the two fault zones, with Ailaoshan fault zone in the east and Lancangjiang fault zone in the west. Luchun arc is formed on the side of Ailaoshan fault and the Chongshan arc is formed on the side of Lancangjiang fault and the arcs are against each other.The exposed part of the researched region in stratigraphic superregion of the southern part of China are Mesozoic stratas and a few of old stratas, that is the Jinggu stratigraphic minor region and Yangbi stratigraphic minor region in the Lanping-Simaostratigraphic regionalization and the Mojiang stratigraphic minor region in the Xijir Ulan-Jinsha River stratigraphic regionalization. As for the exposed part of the eastern and western margin of the basin, there is a big difference in the Palaeozoic stratas and some similarities in the Mesozoic stratas.In the eastern and western of the basin, the Cretaceous and Jurassic strata has a single red color. The Jurassic strata can be divided into the following groups according to their ages from the old stratas to the new stratas:Yangjiang Group (Jiy), Huakaizuo Group (J2h) and Bazhulu Group (J3b), while the Cretaceous strata can be divided into the following groups according to their ages from the old stratas to the new stratas:Jingxing Group (K1j) and the Nanxin Group (Kin). The major depositional environment of the Jurassic strata in the eastern of the basin are lacustrine facies and there are also fluvial facies between the lacustrine facies; the Cretaceous stratas are all river depositional systems and there only existing some differences on micro facies. The size of gravels has a great change from the Yangjiang Group to the Jingxing Group. The appearance of vein quartz gravel in the Jingxing Group (K1j) and Nanxing Group (Kin) shows that after a relatively stable period in the Jurassic system, Ailaoshan orogenic belt has another rapid uplift whose provenance is still from Ailaoshan orogenic belt.The evolution in the eastern of the basin can be divided into four stages:â‘ expand and rift-rifted (valley) basin and the Ailaoshan ocean basin formed;â‘¡subduction-back-arc basin formed;â‘¢collide or slide-foreland basin formed;â‘£thrust and uplift-basin extinction, thrust-nappe, strike-slip and the highland formed. The basin has been determined to be the retroarc foreland basin in Jurassic and cretaceous period.By using the way of fission track T-t Thermal history simulation, we have arrive at that the thrust-uplift and thrust-nappe in the eastern of the basin has a form of forward extention successively from the northeast to the southwest. Though the ways such as kinesiology and geodynamics, we also carry on comprehensive analysis. Starting from64Ma, the researched region begin to turn from subsidence to continuous uplift, which means that there are no palaeogene deposit in the eastern of the basin. From the paleogene period (64Ma) on, the subsidence has turned to uplift in the eastern margin of the basin, therefore, the64Ma has become the starting point of uplift in the eastern of the basin.