A study of detrital zircons of Late Carboniferous-Middle Triassic strata in the northern margin of North China block and its geological implication
MA Shou-xian1,2,MENG Qing-ren1,QU Yong-qiang3 1.Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China; 2.Graduate University of Chinese Academy of Sciences,Beijing 100039,China; 3.Northwest Branch,Research Institute of Petroleum Exploration and Development,PetroChina,Lanzhou 730020,Gansu,China
In order to interpret the uplift history of Inner Mongolia Paleo-uplift and understand the tectonic evolution of Paleo-Asian Ocean,the authors conducted U-Pb dating and Hf isotope analysis of detrital zircons from distinct levels of Late Carboniferous-Middle Triassic strata in Pingquan.U-Pb ages of detrital zircons from five samples fall into five groups,i.e.,Group 1 of Middle-Late Permian(270~250Ma),Group 2 of Late Carboniferous-Early Permian(325~290Ma),Group 3 of Devonian(400~360Ma),Group 4 of Paleoproterozoic(1900~1700Ma) and Group 5 of Neoarchean-Paleoproterozoic(2600~2400Ma).Among these five samples,age spectra of Benxi Formation are composed of Group 3,Group 4 and Group 5,age spectra of Shanxi Formation,Sunjiagou Formation and Liujiagou Formation mainly consist of Group 2 and Group 4,and age spectra of Lower Shihezi Formation are composed of Group 1,Group 4 and Group 5.In addition,zircons from the five samples have the same Hf isotope characteristics.εHf(T) values of Phanerozoic zircons range from-3.2 to-25.5,consistent with the values of Late Paleozoic plutons in Inner Mongolia Paleo-uplift.The zircon age constituents and Hf isotopes suggest a provenance from Inner Mongolia Paleo-uplift,and the zircon age variation through different levels implies two critical uplifting events,which occurred during 360~312Ma and 276~258Ma respectively.360~312Ma uplift built up the tectonic framework of the North China basin and provided sediments for the basin.After 276~258Ma uplift event,Inner Mongolia Paleo-uplift was steadily denuded and thus supplied a great amount of coarse-grained sediments to the sedimentary basin which had unchanged U-Pb age spectra of detrital zircons,suggesting that the Paleo-Asian Ocean might have been closed before 276Ma.
【Fund】： 国家自然科学基金面上项目《燕山构造带中部晚侏罗世火山沉积演化及构造意义》(批准号:40972151);; 中国科学院知识创新工程重要方向项目《外贝加尔-华北断面(南段):地质构造格局及成矿背景》(编号:KZCX2-YW-Q04-04)
【CateGory Index】： P597.3
【CateGory Index】： P597.3