什那干群层凝灰岩夹层SHRIMP锆石U-Pb年代学研究及其意义  

SHRIMP Zircon U-Pb Geochronology of the Tuffite Layer in the Shi’nagan Group,Inner Mongolia,North China Craton

作　　者：苏文博[1] 李文国 李惠民[3] 宋彪[4] 狄永军[1] 周红英[3] 王惠[2] 王健 Frank R Ettensohn Warren D Huff SU Wen-bo;LI Wen-guo;LI Hui-min;SONG Biao;DI Yong-jun;ZHOU Hong-ying;WANG Hui;WANG Jian;Frank R Ettensohn;Warren D Huff(School of Earth-sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Geological Survey,Inner Mongolia Autonomous Region,Hohhot 010020,China;Tianjin Centre,China Geological Survey,Tianjin 300170,China;Beijing SHRIMP Center,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Department of Earth and Environment Sciences,University of Kentucky,Lexington,KY40506-0063,USA;Department of Geology,University of Cincinnati,Cincinnati,OH 45221-0013,USA)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]内蒙古自治区地质调查院,呼和浩特010020 [3]中国地质调查局天津地质调查中心,天津300170 [4]北京离子探针中心,中国地质科学院地质研究所,北京100037 [5]Department of Earth and Environment Sciences,University of Kentucky,Lexington,KY40506-0063,USA [6]Department of Geology,University of Cincinnati,Cincinnati,OH 45221-0013,USA

出　　处：《华北地质》2022年第2期51-67,共17页North China Geology

基　　金：国家自然科学基金项目(41772028,41272046,40772076);国家重点研发计划(2020YFA0714800)

摘　　要：在内蒙古乌拉特前旗大佘太镇附近的什那干群“下岩组”中下部,第一次发现了层凝灰岩等火山沉积夹层,并对其中的层凝灰岩(NM-1191)开展了SHRIMP锆石U-Pb年代学研究,精确标定其喷发时间为1614±8 Ma。由此可以确认,什那干群整体上应属于国际古元古代固结纪(Statherian Period,1800~1600 Ma)末期-中元古代盖层纪(Calymmian Period,1600~1400 Ma)初期(相当于中国中元古代长城纪(1800~1600 Ma)末期-蓟县纪(1600~1400 Ma)初期)沉积。这一新的年代地层学归属的确定,显示什那干群与毗邻的渣尔泰山群及白云鄂博群(化德群)的相应层位,应属于“三群并立”、“同时异相”的沉积古地理格局;同时这也表明,该群基本可与华北克拉通北缘-中部的大红峪组-高于庄组对比,并与南缘洛峪口组-龙家园组大体相当。结合相关资料可进一步推知,位于鄂尔多斯西缘贺兰山-千里山一带的黄旗口组-王全口组及阿拉善南缘龙首山地区墩子沟群中下部(即第一、第二岩组),也应与什那干群的层位基本一致。这一广泛存在的对比关系很可能也说明,至少到中元古代盖层纪早期,阿拉善(阴山)地块仍隶属于华北克拉通的范畴,并与鄂尔多斯西缘、燕辽盆地-华北中部带及熊耳裂谷区等,共同拥有一个统一的“泛华北”陆表海。什那干群新的年代学约束及相关地层单元年代学等时框架的建立,为重新认知该阶段华北克拉通北缘沉积-构造古地理及其演化,探讨华北克拉通与哥伦比亚超大陆关系等重要命题,提供了关键的年代地层学约束。For the first time,the age of an interbedded tuffite layer and related volcanogenic deposits have been determined from the middle of the Lower Formation of the Shi’nagan Group,near Dashetai Town,Urad Front Banner,Inner Mongolia.Using SHRIMP zircon U-Pb ages for the tuffite layer,Sample NM-1191,the weighted mean 207Pb/206Pb age of 1614±8 Ma(n=21,95%conf.,MSWD=0.17)was obtained,which precisely calibrates the time of the corresponding volcanic eruption event.Hence,on the whole,the Shi’nagan Group was probably deposited during the transitional time interval at the end of the Paleoproterozoic Statherian Period(i.e.,the Changchengian Period of China,1800~1600 Ma)to the beginning of the Mesoproterozoic Calymmian Period(i.e.,the Jixianian Period of China,1600~1400 Ma).This new revision of the chronostratigraphy indicates that,during the Paleo-Mesoproterozoic transition interval,all the three groups(i.e.,the Shi’nagan Group,the Zha’ertai Group,as well as the Bayan-Obo Group)in Inner Mongolia were very likely contemporaneous,heterotopic facies that existed side-by-side.In addition,our dating shows that the Shi’nagan Group can be correlated fairly well with the Dahongyu and the Gaoyuzhuang formations in the Yanshan(Yanliao)and the Taihang mountains from the northern to the middle parts of the North China Craton(NCC),respectively.Furthermore,this age means that the Shi’nagan Group may also be equivalent to the Luoyukou and the Longjiayuan formations on the south margin of the NCC.Moreover,in combination with regional geological information,it may be inferred that both the Huangqikou and the Wangquankou formations at the western margin of Ordos Block and the First and Second formations of the Dunzigou Group in the Longshoushan Mountains at the south margin of the Alxa(Yinshan)Block,might be coeval with the Shi’nagan Group.Consequently,this kind of widespread correlation may imply that,at least until to the beginning of the Calymmian Period,the Alxa Block was probably affiliated with the NCC,which was covered by

关 键 词：什那干群 层凝灰岩 锆石U-PB年龄 同时异相 古-中元古代 华北克拉通 

分 类 号：P588.21[天文地球—岩石学] P597.3[天文地球—地质学]