贺根山缝合带阿萨格图钾玄质火山岩锆石LA-ICP-MS U-Pb年龄、地球化学特征及构造意义  

The Asagetu shoshonitic volcanic rocks in the Hegenshan Suture:Zircon LA-ICP-MS U-Pb ages,geochemical features and its tectonic significance

作　　者：王金芳 李英杰 李红阳 董培培 WANG Jinfang;LI Yingjie;LI Hongyang;DONG Peipei(College of Earth Sciences,Hebei GeoUniversity,Shijiazhuang,050031)

机构地区：[1]河北地质大学地球科学学院,石家庄050031

出　　处：《地质论评》2021年第4期918-935,共18页Geological Review

基　　金：国家自然科学基资助项目“内蒙古迪彦庙蛇绿岩带前弧玄武岩组合及其成因”(编号:41972061);中国地质调查局项目“内蒙古1∶5万高力罕牧场三连等四幅区调”(编号:1212011120711);“内蒙古1∶5万沙日勒昭等四幅区调”(编号:1212011120701)的成果。

摘　　要：内蒙古西乌珠穆沁旗阿萨格图火山岩出露于贺根山缝合带迪彦庙蛇绿混杂岩南侧,岩石类型为粗安岩、粗面岩和粗面英安岩。粗安岩锆石LA-ICP-MS U-Pb同位素测年获得火山岩形成年龄为132.1±0.7 Ma。岩石地球化学显示火山岩属于钾玄岩系列,岩石高Na_(2)O+K_(2)O(7.61%~10.35%)、高K_(2)O(3.94%~6.04%)、高Al 2O3(16.32%~17.99%)、低TiO_(2)(0.45%~0.95%),富集Rb、Ba、U等大离子亲石元素(LILE)和轻稀土元素(LREE),亏损Nb、Ta和Ti等高场强元素(HFSE)。稀土元素含量为109.62×10^(-6)~174.68×10^(-6),稀土元素配分曲线为右倾式分布。岩石学和岩石地球化学特征表明,阿萨格图地区白垩纪火山岩与洋壳俯冲作用有关,形成于俯冲板片断离—后造山伸展构造背景。古亚洲洋俯冲洋壳析出流体交代上覆地幔形成贺根山缝合带富集地幔,随后的俯冲板片断离—后造山伸展作用触发富集地幔部分熔融产生该钾玄质岩浆。结合贺根山缝合带的壳幔电性结构和晚古生代蛇绿岩—岛弧岩浆岩、中生代后造山A型花岗岩的时空分布与演化,初步建立了该区钾玄质火山岩的板片断离—后造山伸展地球动力学模式。Objectives:The Hegenshan suture of the eastern Central Asian Orogenic Belt(CAOB)has developed the Late Paleozoic SSZ-type ophiolites—arc magmatic rocks and Mesozoic volcanic rocks.The spatial—temporal distribution and genetic relationship between Mesozoic volcanic rocks and late Paleozoic ophiolite—arc magmatic rocks have gradually become one of the important scientific issues in the tectonic evolution of the Hegenshan suture.Therefore,this study carried out zircon geochronology,geochemistry,genesis and tectonic environment on the Asagetu Mesozoic volcanic rocks in order to provide new evidence for the tectonic evolution of the Hegenshan suture.Methods:Based on field geological surveying,petrology,geochemistry and LA-ICP-MS zircon U-Pb geochronology of the Asagetu volcanic rocks exposed in the sothern part of the Diyanmiao ophiolitic melange belt of the Hegenshan suture in Xiwuqi of Inner Mongolia,this paper discusses petrogenesis and tectonic environment of the volcanic rocks,and slab breakoff—post orogenic extension of the Paleo-Asian Ocean.Results:The Asagetu volcanic rocks are mainly composed of trachyandesite,trachyte and trachydacite.Zircon LA-ICP-MS U-Pb dating for the trachyandesite volcanic rocks shows that the age of volcanic rocks is 132.1±0.7 Ma.Petrogeochemistry shows that volcanic rocks belong to shoshonite series.Rocks with high Na_(2)O+K_(2)O(7.61%~10.35%),K_(2)O(3.94%~6.04%),Al 2O3(16.32%~17.99%)and low TiO_(2)(0.45%~0.95%)are obviously enriched in LILEs(Rb,Ba and U)and LREEs,and depleted in HFSEs(Nb,Ta and Ti).The contents of rare earth elements range from 109.62×10^(-6) to 174.68×10^(-6).The chondrite normalized REE distribution patterns are of right inclined shape.Combined with the crust—upper mantle electrical structure and the temporal—spatial distribution of the Late Paleozoic ophiolites—arc magmatic rocks and Mesozoic post orogenic A-type granites in the Hegenshan suture,the geodynamic model of the subducted slab break off—post orogenic extension of the shoshonitic volca

关 键 词：钾玄质火山岩 板片断离 后造山伸展环境 早白垩世 贺根山缝合带 

分 类 号：P597.3[天文地球—地球化学] P588.14[天文地球—地质学]