The Research On Relationship Between Paleogeothermal Evolutional History And Various Mineral Deposits In Ordos Basin

By principles of integrated,dynamic and comprehensive basin analysis,research were made in Ordos basin using vitrinite reflectance, homogenization temperatures of fluid inclusion and apatite fission track on base of geological,geophysical and geochemical methods.Progresses are made according to research of paleogeothermal field and present geothermal field and thermal evolutional history in the Ordos basin.On the regression analysis from large numbers of thermometric data,results show that the Ordos basin is a middle-temperature style geothermal field,present average geothermal gradients is 2.9 ℃ /100m, average value of thermal flux is about 61.8mW/m~2 of the whole basin near to the middle value of the average thermal flux all the world.Present geothermal gradient and geothermal flux of the Ordos basin is controlled by the thickness of the earth crust in the different tectonic element and the thickness of lithosphere.The thermal evolutional history is recovered by means of many kinds of paleothermometric methods integrating tectonic evolutional history of the basin.Both Palaeozoic era geothermal gradients and Mesozoic era geothermal gradients are low (2.2~3.0℃/100m) .geothermal gradients is elevetory to 3.3—4.1 ℃/100m in the aftermoon of Mesozoic era,geothermal gradients failed to 2.8℃/100m little by little since Cenozoic ear, the average paleogeothermal gradient is about 4.0 ℃/ 100m, which is obvious higher than present geothermal gradient.The Ordos basin on late-Mesozoic exist on a tectonic heat event.It is decided that tectonic heat event occurred on 100 ~ 140Ma of early-Cretaceous period in late-Mesozoic,continuous time of tectonic heat event is about 10~40Ma.Tectonic heat event have function in controlling formation, evolvement and the formation stages of oil-gas reservoirs and coal.Later of Yanshan movement is main period of oil-gas migration and congregation,it is also main period of coalification inPermo-Carboniferous system ^ Triassic system and Jurassic system.Large scale of elevation and denudation happened later in Ordos basin,it is first recovery of denudation thickness by using the relation between Specific thermal conductivity and depth.It is recovery of denudation thickness of the different tectonic element on base of the relation between vitrinite reflectance and depth.Denudation thickness take turns to increase according to the sequence of Tianhuan syncline, fault-fold belt of west margin, Yimeng uplift, Yishan slope, Jinxi fault-fold belt,Weibei uplift.Thermal evolutional history in Ordos basin controls the formation and evolvement of oil and gas and coal,it also controls the formation period of uranium.The max paleogeothermal values of stratum were reached in the early-Cretaceous period according to the simulation result of basin thermal history,the period of tectonic heat event happened in the early-Cretaceous period is the main formation period of gas in coal stratum of Palaeozoic era,it is also the formation period of metal uranium in Dongsheng area.Oil and gas of the early-Cretaceous formation migrated from Yimeng uplift to Dongsheng aera,it had reducing agent function on the formation of uranium.