Mesozoic-cenozoic Tectonic-thermal Geochronology Of The Eastern Margin Of The Ordos Basin

The eastern margin of the Ordos Basin is an important coal gas producing areas in China,do the basic geological research on the basin-mountain and exhumation history has an important and far-reaching significance for the exploration and development of coalbed methane.This paper mainly through study the field geological survey,indoor seismic interpretation and apatite fission track reveals the Mesozoic-Cenozoic tectonic thermal evolution history of this region.Based on the research of fold and fault in the field and preliminary interpretation of seismic profile of the eastern margin of Ordos basin,the result show that the structure geology of this region is relatively simple,and it closely related to the Indo-china movement,Yanshan movement and Himalayan movement.The exposed attitude of stratum gently tilted towards the west,the angle is 2°～10°.Most faults in the outcrops are normal faults and those faults’ displacement are 1々3 m and the fault fracture zone undeveloped.Most types of folds in this area is broad and gentle fold,and the trend is generally NE,NNE.The seismic data in the south of Yanchuan area also showed that the stratum inclines gently towards the west,also it can be divided into three parts,namely the central fracture zone,the western faulted nose structure zone and the eastern slope belt zone.Through the apatite fission track test on the mountain Lvliang and basin,we can use it to research tectonic-thermal evolution of the mountain and basin.It is significant to understand the process of the North China craton evolution and destruction.The tests show that the age of apatite in the Mountain Lvliang distribution in 138Ma～48Ma.Cross-sectional view of the fission track ages and valley topography is basically in agreement.Through the age-elevation relationship,we can calculate the rate of uplift of mountain is 7.35m/Ma,the R-squared reached 0.7.And also the length of confined fission track and the fission track age has a negative correlation.The age of detrital apatite fission track in the basin distributed from 50Ma to 39Ma.Through the age-elevation relationship,we can calculate the rate of uplift of basin is 12.2m/Ma,the R-squared reached 0.99.Through the thermal history modeling to all the sample,we can see that from the Early Jurassic-Early Cretaceous to Eocene,the mountain uplift was slowly,and after that accelerate away from the PAZ.The basin samples enter the PAZ after the Late Cretaceous,and then accelerated uplift,at last away from PAZ in the Miocene.By using the Neogene pale magnetic stratigraphy and sedimentary facies analysis in the Piedmont of Lvliang,we can know that the basin-mountain coupling further developed up in the Pliocene and the mountain Lvliang further extended and became orogeny,the graben of Fenwei,in eastern of Mountain Lvliang,sunk and accepted sediments deposited.