| The interaction between the continental-continental collision of the Indian-Eurasian plate and the two sub-diving systems of the Pacific plate are generally considered to be the reasons of the destruction of North China Craton.At present,the global researches which are about the dynamic mechanism of the formation and evolution of the Ordos fault depression system and the tectonic stress field still have doubts.The Hetao basin is the northern edge of the Ordos block and the northern part of the Yinshan block.The formation of the Hetao basin has been affected by the role of each plate since the beginning of the Eocene,mainly due to the uplift of the Qinghai-Tibet Plateau and the western subduction of the Pacific plate.Finally formed the NNE-NE direction as the main compressive stress.The stress field is the leftward tension band of the SN pull.Hetao ancient lake is a lake formed in late pleistocene and located in Hetao basin,the disappearance of Hetao ancient lake is mainly because of tectonic action.However,the relationship between the disappearance of the Hetao ancient lake and the activity of the rupture of the surrounding ridge in the Hetao basin has not yet been reasonably researched and explained.In this paper,through the detailed study about the sedimentary facies of the lacustrine facies near the trench in the Donghe area of Baotou,we could measure the time of the Daqingshan movement.Then we could obtain the evolution history of the Hetao ancient lake.Based on these information,the characteristics of the tectonic stress field in the Hetao basin are further deduced from the later Pleistocene geological events of the Ordos block.To get the influence of the Daqingshan movement on the Hetao basin,the work of this paper mainly includes the following two aspects: Firstly,the Haolaigou profile is used as the starting point,the influence of Daqingshan movement on the current tectonic stress field of Hetao basin is analyzed by combining the previous research results with the previous research results.Secondly,on the basis of making sufficient use of the research results of predecessors,this paper has obtained basic data such as Quaternary standard drilling,field geological survey and sample test results in Baotou City.We also use tectonic geology,Quaternary geology,Stratigraphy,sedimentology and a variety of dating methods to carry out a comprehensive study,made the following research results:(1)The sedimentary model of the trench and the upper lacustrine facies is a ubiquitous depositional model in the Daqingshan area.This type of deposition is also distributed in the Langshan piedmont fault.Therefore,we condider that this unconformity appearing in the northern margin of the Hetao basin is a widely distributed phenomenon.The formation of unconformity mans the occurrence of a regional tectonic movement.(2)The results of the lacustrine stratigraphic formation in the trenched gully area show that the disappeared time of the unconformity is about 80,000 years ago.Then because of subdued intensity of the fault activity in the northern edge of Ordos,the ancient lake spilled over the mountains again until the ancient lake disappeared during the period between 60,000 years and 30,000 years ago.During this period,the rupture of the northern margin of the Hetao basin is in the tectonic turbulence,which is the movement of the Great Castle Peak.(3)In this paper,we used the previous studies of the activity of the Ordos block and its peripheral fault depression system,and combined with the observation of the current GPS velocity field and the anisotropy of the seismic wave of the upper mantle material in the Hetao basin.We consider that the Hetao basin is affected by the NE-SW expansion effect.The main reason is that the northward expansion of the Qinghai-Tibet Plateau had affected the Hetao basin in the late Pleistocene and caused the gradually strengthened activity of the northern part of the Hetao Basin.Based on the work done in this paper,we not only obtain the time of the Daqingshan movement and its influence on the Hetao basin,but also acquire the dynamic mechanism of the formation and evolution of the Ordos peripheral fault depression system.This paper provides a theoretical basis to the study about the effect of the destruction of the North China craton from the Cenozoic.It has great significance and value for the further improvement of the geological work in whole North China. |
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