Research Of The Mesozoic And Cenozoic Structural Features In The Southwest Of Ordos

The southwest of Ordos spans Ordos’s west thrust belt,Tianhuan depression, north Qilian and north Qinling thrust—nappe structures,northern uplift to Wei river,Fenwei graben and Xiaoqinling structure belt. Different tectonic systems at different stages were added together and the same tectonic system at different stages was added’together,which makes today’s structure and its evolutionary features extremely complex.Yanshan period is not only the key stage at which the foudermental tectonic pattern today was formed in the research region,but is the key period of petroleum and gas accumulation as well.The Hymalayan movement then reformed the pattern.All these things show that the research on the features of Mesozoic and Cenozoic structures in the southwest of Ordos is particularly important,Basaed on plate tectonics,structural geology and basin—range coupling theory, the author makes a research on the basement structure, structure pattern of caprock,structural deformation features at different tectonic areas and different tectonic depths in the view of history and evolution and establishes the three dimentional structure model today of the research region by means of field geolongical survey and geophysical data processing and comprehensive interpretation. By processing and interpreting of gravitational and aeromagnetic data,reinterpreting some of the seismic profiles and CEMP profiles and taking5backbone geological—geophysical comprehensive interpretation profiles which cross west and south of Ordos,relevant supporting profiles and key structural sectors as the focus of research,the author makes a sophisticated research.The results of the research show that north Qilian and north Qinling thrust—nappe structures’crystalline basement is quite different from that of north China block and the crystalline basement of north China block in the research area consists of2NE basemental uplifts and2basemental rifts;there is discordance beteen deep structures and superficial structures in the research region; Haiyuan—Luonan fault extends from Tieluzi to the west along Wangqu—Yabai fault which extends to the west and is connected with Badu—Guozhen fault; Shengrenqiao—Sanmenxia—Huainan fault is the border of Ordos’s west thrust belt which extends west from Fuping to near Qianyang and is buried under the basin,and it is speculated that the fault extends east to Sanmenxia within the research region; the northern edge fault of northern uplift to Wei river is the border beteewn Ordos stable block and the Yanshan period structure belt of south Ordos; During Yanshan period south Ordos is a huge anticlinorium whose core is located at Wei river basin and whose northern wing is northern uplift to Wei river and Xiaoqinling structure belt and Luonan region are the syncline which matches the anticlinorium,and there probably aren’t upper Paleozoic and Mesozoic in Wei river basin;in Ordos’s west thrust belt, the steep dipping Ordovician,Cambrian system and Jixian system are located at the parts of Qinglongshan—Pingliang fault’s hanging wall which are near the fault and Tianshuibu—Sishilipu low uplift belt,where the main structure pattern is high—angle thrust structure and no overthrust nappe exists.