Provenance Of Chang7-Chang4+5 Strata,Yanchang Formation In Southeastern Ordos Basin:Constraints From Detrital Zircon U-Pb Ages

This paper focus on the Provenance source of Chang7-Chang4+5 Strata,Yanchang Formation in Huanglong,Huangling and Jinsuoguan areas,southeastern of the Ordos Basin with the LA-ICP-MS zircon U-Pb isoptope geochronologic method.The results show that the detrital zircons of sandstone from Jinsuoguan area has six age ranges:2700?2300Ma,2300?1600Ma,1100?800Ma,500?400Ma,355?255Ma and 255?212Ma,Huanglong and Huangling lost 1100-800Ma age ranges,the rest five groups are distributed.These six age ranges in the study area respectively respond to their own tectonic event in the Neoarchean-Early early proterozoic,Early early proterozoic-Late early proterozoic,Late Mesoproterozoic-Early Neoproterozoic,Early Paleozoic Caledonian,Hercynian and Indosinian.By comparing the zircon age of the study area with the age structure of the surrounding terranes and combining with the the sedimentary facies,paleocurrent,heavy mineral.analysis of the Yanchang Formation in the study area,the following conclusions are obtained:1.The provenance of Chang7-Chang4+5 Strata of the southeastern part of the Ordos Basin is mainly from the northern margin of the North China Block(Yinshan Terrane,Khondalite Belt),the southern margin of the North China Platform,North Qinling orogenic belt and magmatic rock in Variscan-Indosinian.It was deeply found that,the provenance of Chang7-Chang4+5 Strata in Jinsuoguan mainly effected by the North Qinling(Erlangping group,Danfeng group,Kuanpin Group,Qinlin Group and other metamorphic rock series)and the southern margin of North China(the basement rocks,Xiong'er group,Alkaline granite,Indosinian magmatic rocks).The provenance of Chang7-Chang4+5 Strata in Huanglong and Huangling is Yinshan(gneissic granite,ancient TTG gneiss and granulite),Khondalite Belt(early Proterozoic),magmatic rocks(Hercynian and Indosinian).2.Former studies found that early Yanchang Formation in Jinsuoguan hadn't affected by the North Qinling material source,while this paper find some proterozoic age of North Qinlin in Jinsuoguan areas,indicating that the southern Qinling source began to affect the region.It shows that from the beginning of Chang 7 due to the Qinling orogenic tectonic activity increased,Which makes the source of Qinling in the southern part of the basin gradually migrate northward and the source of the northern source of the phenomenon of the shift.Combined with the difference of Zircon age structure,sedimentary facies,paleocurrent,heavy mineral analysis of Chang7-Chang4+5 Strata in the study area,authors believe that there may be a small deposition center in the Tongchuan area of the southeastern Basin in Chang7-Chang4+5.It segments northeastern and southern material source of the study area.