西藏隆巴俄桑地区玄武岩与安山玢岩的地球化学:对班公湖-怒江洋构造演化的启示  

Geochemistry of Basalt and Andesitic Porphyrite in Longbaesang Area, Tibet:Implications for the Tectonic Evolution of the Bangonghu-Nujiang Ocean

作　　者：尹滔[1] 尹显科[1] 秦宇龙[1] 裴亚伦[1] Yin Tao;Yin Xianke;Qin Yulong;Pei Yalun(Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province,Sichuan Geological Survey,Chengdu 610081,China)

机构地区：[1]四川省地质调查院稀有稀土战略资源评价与利用四川省重点实验室,四川成都610081

出　　处：《地球科学》2020年第7期2345-2359,共15页Earth Science

基　　金：中国地质调查局项目(Nos.DD20160026,DD20191029)。

摘　　要：狮泉河-永珠-嘉黎蛇绿混杂岩带的构造属性及其与班公湖-怒江缝合带演化的关系,是了解班公湖-怒江洋中生代构造演化的关键.对隆巴俄桑地区的玄武岩和安山玢岩脉开展了岩石地球化学研究.结果表明,玄武岩属拉斑玄武岩系列,富集LREE和大离子亲石元素Rb、Ba、K、Sr、Pb等,亏损高场强元素Nb、Ta、Ti,与岛弧拉斑玄武岩特征一致.安山玢岩脉属拉斑玄武岩系列,有向钙碱系列演化的趋势,富集大离子亲石元素Rb、Ba、K、Sr、Pb、U等,亏损高场强元素Nb、Ta,显示岛弧成因岩浆岩地球化学特征,低ΣREE(11.8×10-6~13.8×10-6),(La/Yb)N=0.37~0.43,亏损LREE,与N-MORB相似,具有岛弧岩浆岩(IAB)和正常洋中脊玄武岩(N-MORB)双重特征,与不成熟的弧后盆地玄武岩(BABB)特征一致.综合区域地质资料认为,隆巴俄桑玄武岩和安山玢岩形成的构造环境均与俯冲相关,可能分别形成于班公湖-怒江洋壳南向俯冲消减相关的洋内或者活动大陆边缘的岛弧环境和不成熟的弧后盆地环境,是中侏罗至早白垩世期间班公湖-怒江洋壳南向俯冲消减的再循环的产物.The tectonic nature of Shiquanhe-Yongzhu-Jiali ophiolitic mélange zone andits relationship to the Bangonghu-Nujiang suture zone are key to understanding the Mesozoic tectonic evolution of the Bangonghu-Nujiang Ocean.Geochemistry of basalt and andesitic porphyrite in Longbaesang area are reported in this paper.The results show that the basalt are tholeiitic rocks,and enriched in light rare earth elements and large ion lithophile elements(Rb、Ba、K、Sr、Pb),and depleted Nb,Ta,Ti.All of the geochemistry characteristics of the basalt rocks are the same as typical of island arc tholeiite.The andesitic porphyrite are tholeiitic rocks,which has the trend of evolution to calc alkaline rocks,enriched large ion lithophile elements(Rb、Ba、K、Sr、Pb、U),depleted Nb,Ta,clearly displaying compositional characteristics of island-arc volcanic rocks.Additionally,the compositional characteristics of lowerΣREE(11.8×10-6-13.8×10-6)、(La/Yb)N(0.37-0.43)and depleted in light rare earth elements,which are also Similar to normal mid-ocean ridge basalt,Therefore,the andesitic porphyrite may be formed in a immature back-arc basin.Combined with the regional geological data,the tectonic environment of the basalts and andesitic porphyrites both are related to subduction,which respectively,may be formed in the oceanic or the active continental margin of island arc environment and the immature back-arc basin environment,related to the South subduction of Bangonghu-Nujiang ocean crust,which are record the recycling of the Southern subducted Bangonghu-Nujiang oceanic crust during the late Jurassic to the early Cretaceous.

关 键 词：岩石成因 俯冲消减 弧后盆地 狮泉河蛇绿混杂岩 班公湖-怒江缝合带 构造地质 

分 类 号：P581[天文地球—岩石学]