中祁连西段野马河一带埃达克质花岗岩成因及构造意义  

Genesis and tectonic significance of Adakite granite in the Yemahe area of the western section Middle Qilian

作　　者：张立涛 戴霜 张在嘉 杨镇熙 杨永春 ZHANG Li-tao;DAI Shuang;ZHANG Zai-jia;YANG Zhen-xi;YANG Yong-chun(School of Earth Sciences,Lanzhou University,Lanzhou 730000,China;Key Laboratory of Mineral Resources Exploration,Gansu Province,Fourth Institute of Geological and Mineral Exploration,Gansu Bureau of Geology and Mineral Resources,Jiuquan 735000,Gansu,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,兰州730000 [2]甘肃省地质矿产勘查开发局第四地质矿产勘查院,甘肃省矿产资源勘查重点实验室,甘肃酒泉735000

出　　处：《兰州大学学报(自然科学版)》2025年第2期190-200,共11页Journal of Lanzhou University(Natural Sciences)

基　　金：中国地质调查局项目(DD20160012);甘肃省科技计划项目(22JR5RA819);甘肃省重点人才项目(2023RCXM04)。

摘　　要：对中祁连西段野马河一带地区识别出的具有典型埃达克岩特征中酸性侵入岩进行锆石U-Pb年代学和岩石地球化学研究.野马河一带花岗闪长岩LA-ICP-MS锆石U-Pb加权年龄最早为472.8±2.0 Ma,最晚为462.9±1.8 Ma,岩体位于中奥陶世.地球化学数据表明,岩石中w(SiO_(2))=63.97%~72.90%,w(Al_(2)O_(3))=14.78%~18.16%,w(K_(2)O)=1.48%~2.18%,w(Na_(2)O)=2.88%~5.32%,w(Na_(2)O)/w(K_(2)O)=1.24~3.01,平均为2.21.w(MgO)=0.45%~1.75%,平均1.07%,Mg^(#)(Mg/(Mg+Fe)物质的量比值)多在32~46.岩石整体富Na和Al,贫K和Mg,为弱过铝质岩系.相对富集Rb、Th、Ba、轻稀土(LREE)等大离子亲石元素,亏损Nb、Ta、U等高场强元素,具有高Sr低Yb、Y特征,属埃达克质岩石.岩石中稀土总量变化大,LREE富集,重稀土亏损,轻重稀土分馏明显.地球化学特征显示其为玄武质岩浆底侵诱发的下地壳部分熔融的埃达克岩,与洋壳俯冲形成的埃达克岩特征差异明显,预示北祁连洋向南俯冲的可能性不大.其成因可能是北祁连洋洋脊扩张,洋壳与中祁连陆块强烈挤压,导致中祁连地壳褶皱加厚,同时引发玄武质岩浆底侵,最终诱发下地壳基性物质部分熔融而形成了埃达克质岩侵位.The Middle Qilian magmatic arc is located along the southern margin of the North Qilian arcbasin system,representing a pivotal region for investigating the tectonic evolution of the North Qilian Ocean,particularly with regard to the contentious subduction direction during the Ordovician period.We identified in there intermediate-acid intrusive rocks exhibiting typical Adakite characteristics from the Yemahe area located in the western section of the Middle Qilian,and subsequently conducted studies in zircon U-Pb chronology and petrogeochemistry.Our findings indicated an earliest age of 472.8±2.0 Ma and a latest age of 462.9±1.8 Ma,as determined through LA-ICP-MS zircon U-Pb dating of granodiorite samples from the Yemahe area.These results suggested that the rock body emplacement originated during the early-middle Ordovician.w(SiO_2)=63.97%-72.90%,w(Al_2O_3)=14.78%-18.16%.w(K_2O)=1.48%-2.18%,w(Na_2O)=2.88%-5.32%.w(Na_2O)/w(K_2O)=1.24-3.01,with an average of 2.21.w(MgO)=0.45%-1.75%,with an average value of approximately 1.07%.The majority of Mg#values were between the range of 32-46.The rocks were rich in Na and Al,and poor in K and Mg.They belonged to weakly peraluminous rocks as a whole.Trace elements had been enriched in large ion lithophile elements such as Rb,Th,Ba and LREE(light rare earth elenments),and deficient in high field strength elements such as Nb,Ta and U,of adakite rocks with high Sr and low Yb and Y characteristics.The total amount of rare earth elements varied greatly in the rocks,in which LREEs were enriched,and heavy rare earth elenments depleted.Fractionation of light and heavy rare earth elements had been obvious.The geochemical characteristics indicated that the observed Adakite had been a result of partial melting in the lower crust triggered by invasion of basaltic magmatic floor,distinguishing it from Adakite formed through oceanic subduction.These findings suggested that there had been an unlikely North Qilian Ocean subduction towards the south.This phenomenon could be attributed to th

关 键 词：埃达克质岩 岩石成因 底侵作用 下地壳 中祁连西段 

分 类 号：P581[天文地球—岩石学] P548[天文地球—地质学]