A Study Of Tectonic-thermal Evolution History Of Meso-Cenozoic Yimeng Uplift In The Ordos Basin

The study on the tectonic-thermal evolution history of Ordos Basin has a history of nearly 50years,but the study on Yimeng Uplift in the north of Ordos Basin still needs to be further strengthened.Since Mesozoic,many tectonic activities have taken place in Yimeng Uplift,which has a far-reaching impact on the surface lithosphere,and also caused some damage to the migration and accumulation of oil and gas resources.Therefore,it is of great geological significance to study the tectonic-thermal evolution history of Yimeng Uplift.Starting from the current geothermal field of the basin,the physical properties of some cores,such as heat generation rate and thermal conductivity,are tested for some wells with comprehensive well location data,so as to restore the current geothermal gradient and geothermal flow of the basin.The current geothermal gradient of Yimeng Uplift is2.91?/100m.By drawing the plane distribution map of geothermal flow,it is found that the geothermal flow is mainly distributed in the range of 58m W/m²-66m W/m²,and the contour line is distributed in the east-west direction.In the south of Hangjinqi to Dongsheng line,the geothermal flow is less than 64m W/m²,and increases to 70m W/m²to the north.After the test and simulation of vitrinite reflectance Ro of coal and solid asphalt,the plane map and vertical characteristic map of thermal evolution degree of Yimeng Uplift are drawn.It is concluded that the vitrinite reflectance value in this area is low,and Dongsheng area is far lower than the southwest area of Hangjinqi to Yijinhuoluoqi line.According to the results of Petro Mod simulation,it is found that the thermal evolution degree of Permo Carboniferous system is higher and the hydrocarbon generation threshold time is earlier.Based on the fission track dating method,the temporal and spatial distribution characteristics of apatite fission track ages in Yimeng Uplift are analyzed.It is found that the tectonic evolution of Yimeng Uplift has the characteristics of strong in the east and weak in the west,early in the east and late in the west since Mesozoic.Combined with vitrinite reflectance and other parameters in Yimeng Uplift area,the paleogeothermal gradient of Early Cretaceous is3.3?/100m,and that of Dongsheng area is 3.9?/100m,which indicates that the paleogeothermal gradient is significantly higher than the present one due to large denudation thickness and differential denudation.And its thermal evolution history can be roughly divided into the following three stages:Early Triassic to Late Jurassic heat flow rising stage(T₁-J₃),late Jurassic to Early Cretaceous maximum heat flow peak(J₃-K₂)and Late Cretaceous to present heat flow decline stage(K₂-Q).Though the burial history and previous research results,it can be determined that there was one large-scale hydrocarbon accumulation timing in Mesozoic of Yimeng Uplift,which was in Early Cretaceous(120Ma-100Ma).