| The Weibei uplift and the Qinling orogenic belt are adjacent to the Weihe basin,the tectonic-thermal evolution,especially the process of differental uplifting since the late Mesozoic,has been a hot issue for research on basin-mountain relationships and the oil-gas exploration in the southern Ordos basin.In this study,field structural section analysis,seismic section analysis and tectonic-thermal geochronology analysis are applied to discuss the superimposed complex relationship in the late Caledonian and the middle Yanshanian,as well as the structural zoning characteristics,the tectonic thermal events of the late Mesozoic and the later stage of the uplifting and cooling process,together with the relationship between the process of differential uplift and the activity of adjacent tectonic zones in the later stage.In this study such conclusion can be drawn:(1)Combination of field structural section analysis and seismic section interpretation come to the conlusion that the Weibei uplift area has experienced two crustal faults at least,which were controlled by different orogenic events in the late Caledonian and the middle Yanshanian.The ductile-brittle fracture layer in the late Caledonian was mainly remnant in the south of the Shengrenqiao-Tongguan fault,the brittle fracture layers in middle Yanshanian can be extended to the Lingtai-Huangling fault.The post-differential uplift and the superimulation of the Weihe fault depression are finally characterized by the tectonic unit zoning of "Subsection in the west-east orientation,zoning in north-south orientation" of the Weibei uplift.(2)Statisticanalysis of vitrinite reflectance data and geothermal history simulation reveal that in the middle Yanshanian(140～120Ma)Weibei uplift experienced an important tectonic-thermal event which near the basin,the paleogeothermal gradient was up to 40-50℃/km,significant higher than the present geothermal gradient(29.4 ℃/km).The combination of pre-Cenozoic sedimentary conditions and tectonic thermal events not only results in the high or mature thermal evolution stage(Ro>1.8～2.4%)in the late Paleozoic source rocks,but the"High in north,southeastern margin of the western part of the local tectonic-magmatic thermal anomaly" thermal evolution degree zoning characteristics.(3)Fission track and the difference zoning characteristics maily document and reflect the three periods of uplift-cooling maximum age which are 174～168Ma(the early Yanshanian),116-100Ma(Mid Late Yanshanian period)and 39-27Ma(Mid Late Himalayan period)respectively.The lifting process of Weibei Uplift has the features with early in the southwest part(155-65Ma),late in the north east part(66～32Ma)after the late Mesozoic.(4)Apatite fission track thermal history simulation and differential uplift rate analysis results reveal that the differental uplifting of the Weibei has a trend of firstly(120～65Ma)fast(56～61m/Ma),secondly(65～30Ma)slow(5～10m/Ma)and lastly(30～5Ma)faster(67～85m/Ma)after Mid Late Yanshanian period.For details,Weibei uplift inner belt shows a fast uplift(56m/Ma)in 120～110Ma,slow uplift in 110～40Ma(5m/Ma)and faster uplift(67m/Ma)after 40-17Ma and Weibei uplift outer belt shows fast uplift(61m/Ma)in 120～65Ma,relatively slow uplift in 65～30Ma(lOm/Ma)and faster uplift(85m/Ma)after 30～5Ma. |
