Study On The Formation And Evolution Mechanism Of The Majiatan Tectonic Belt In The Southern Segment Of The Western Margin Of The Ordos Basin

Majiatan tectonic zone is located in a very special structural location which is among the Helan-Yinchuan extensional tectonic system,Liupanshan thrust structural system and Ordos plots.Its formation and evolution is due to the interaction of the surrounding tectonic units,and the study of the formation and evolution mechanism of the Majiatan tectonic zone has important regional tectonic significance.Lots of studies have been done,and many achievements and knowledge about the Majiatan tectonic zone have being acquired,The thrust nappe structure model on the large slip surface has been recognized by most scholars.However,the mechanism of formation and evolution is not clear,so further study is needed.In order to understand the formation and evolution mechanism of Majiatan tectonic zone,First,I analysed the planes of unconformity formed since indochina period,and limited the occurrence time in Majiatan tectonic zone and adjacent areas of the main tectonic deformation,combined with the former research achievements of low-temperature thermochronology,sedimentology.Then interpreted the four seismic profiles across the Majiatan tectonic zone and finished the depth conversion and denudation recovery of them.Then balanced the four cross sections,analysed evolutionary process of Majiatan tectonic zone,and calculated the Shortening amount and the shortening rate of various strata.Based on the comprehensive analysis of the inversion model of the Majiagou tectonic zone,the following conclusions are obtained:(1)The northern and southern parts of the Majiatan tectonic zone belong to different types of tectonic patterns and formed by different formation causes.The deformation of the northern is not very sharp,which influenced and controlled by the Helan-yinchuan tectonic system,and formed the structure of the fold and fracture.The southern is influenced and controlled by the Helan tectonic system,and formed a thrust nappe structure.(2)There is a large slip plane In the carboniferous-Permian of Majiatan tectonic zone.The tectonic deformation mainly happens in the strata above the slip plane,the lower strata was deformed little.(3)The influence of the Indosinian movement on the Majiatan tectonic zone is not very strong,mainly slight fold effect,and accompanied by the existence of the ancient rupture of the weak activities.(4)The present tectonic pattern of Majiatan tectonic zone is mainly formed in the Yanshan period-Himalayan period,and the late Yanshan period laid the general structure pattern,further develop was happened in Himalayan period,The main tectonic deformation was occurred at the end of the Jurassic.