内蒙古西乌旗米斯庙蛇绿岩的识别及其地质意义  

Discovery and significance of the Misimiao ophiolite in Xi U jimqin Banner,Inner Mongolia

作　　者：李英杰 王金芳 董培培 李红阳 张夏炜 王帅 LI YingJie;WANG JinFang;DONG PeiPei;LI HongYang;ZHANG XiaWei;WANG Shuai(Hebei Key Laboratory of Strategic Critical Mineral Resources,Heibei GEO University,Shijiazhuang 050031,China;Hebei Province Collaborative Innovation Center for Strategic Critical Mineral Research,Hebei GEO University,Shijiazhuang 050031,China)

机构地区：[1]河北地质大学,河北省战略性关键矿产资源重点实验室,石家庄050031 [2]河北地质大学,河北省战略性关键矿产研究协同创新中心,石家庄050031

出　　处：《岩石学报》2023年第5期1305-1321,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(141972061);中国地质调查局项目(1212011120701、1212011120711、DD20160041)联合资助。

摘　　要：内蒙古西乌旗新发现的米斯庙蛇绿岩,位于中亚造山带东段迪彦庙SSZ型蛇绿岩带的西延米斯庙一带。大比例尺填图结果显示,米斯庙蛇绿岩呈NEE向展布,宽约5km,长约20km,蛇绿岩各单元出露较齐全,岩性主要为蛇纹石化方辉橄榄岩、暗色均质辉长岩、浅色均质辉长岩、斜长岩、枕状前弧玄武岩(fore-arc basalt,FAB)、枕状过渡熔岩和泥质硅质岩,局部见斜长花岗岩侵入于玄武岩之中,其岩性组合和岩石序列可与代表洋内初始俯冲的迪彦庙前弧蛇绿岩相对比。该米斯庙蛇绿岩岩石序列中辉长岩锆石U-Pb年龄为336.5±3Ma,与东部迪彦庙蛇绿岩的辉长岩同期。米斯庙FAB主要发育无斑结构和少斑结构,基质为球颗结构,枕状构造;枕状过渡熔岩,发育斑状结构,比FAB具有更多的斜长石斑晶。米斯庙FAB地球化学成分与大洋中脊形成的强亏损玄武岩相似,但与N-MORB相比,高场强元素(HFSE)Nb和Ta等含量略低于N-MORB,与弧拉斑玄武岩相似;与米斯庙FAB相比,米斯庙枕状过渡熔岩的地球化学特征是更加亏损Ti、HREE和HFSE,指示大洋板片的渐进性俯冲,类似于IBM前弧的演化。米斯庙蛇绿岩与迪彦庙前弧蛇绿岩均发育类似于马里亚纳前弧的FAB序列,两者延伸长度可达40km,表明在古亚洲洋东段早石炭世沿迪彦庙-米斯庙一带发育洋内初始俯冲,记录了早石炭世古亚洲洋东部洋内初始俯冲事件。The newly discovered Misimiao ophiolite in Xi U jimqin Banner,Inner Mongolia,is located in the eastern part of the Central Asian Orogenic Belt(CAOB)and located in the Misimiao area where the Diyanmiao SSZ-type ophiolite belt extends westward.A detailed large-scale mapping of the Mesimiao ophiolite shows that the Misimiao ophiolite is NEE-oriented,with a width of about 5km and an extension of about 20km.The suite preserves a well-exposed and a nearly-complete ophiolite stratigraphy,and includes,from bottom to top,serpentinized harzburgite,dark isotropic gabbro,light isotropic gabbro,anorthosite,fore-arc basalt(FAB)and pillow transitional lava,with overlying argillaceous chert and plagiogranite veins locally intruding the basalt.This Misimiao ophiolite is consistent with the lithologic assemblage of the Diyanmiao fore-arc ophiolite,which represents the subduction initiation of oceanic slab.The zircon age of the gabbro in this sequence is 336.5±3Ma,which coincides with that of gabbro in the Diyanmiao ophiolite.The Misimiao FABs are aphyric and hypoporphyry,with pillow structure,and the Misimiao transition lavas are porphyritic with more plagioclase porphyry than the FAB.The geochemistry composition of the Misimiao FAB is similar to that of the strong depleted basalts formed on the normal mid-ocean ridge(N-MORB),but the high field strength elements(HFSE),such as Nb and Ta,are slightly lower than those of N-MORB,similar to those of island arc tholeiite(IAT).The geochemistry features of the Misimiao transitional lavas are more depleted of Ti,HREE and HFSE than those of the Misimiao FAB,indicating progressive subduction of the oceanic plate,similar to the evolution of the IBM fore-arc.From the FAB sequence similar to the Mariana fore-arc in the eastern Diyanmiao fore-arc ophiolite to the newly discovered Misimiao ophiolite in the western part,the FAB sequence extends to 40km.It is indicated that the Early Carboniferous subduction initiation developed along the Diyanmiao-Mismiao area in the eastern part of the Paleo-Asi

关 键 词：初始俯冲 米斯庙SSZ型蛇绿岩 早石炭世 古亚洲洋 内蒙古 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]