藏北安多县白垩纪马登火山岩地球化学特征及地质意义  

GEOCHEMICAL CHARACTERISTICS AND ITS GEOLOGICAL IMPLICATIONS OF MADENG VOCANIC ROCKS IN ANDUO,NORTH TIBET

作　　者：费光春[1,2] 赵发明[3] 许家斌[4] 李佑国[1] 

机构地区：[1]国土资源部构造成矿成藏重点实验室,四川成都610059 [2]成都理工大学地球科学学院,四川成都610059 [3]四川省地质矿产勘查开发局404地质队,四川西昌615000 [4]四川省地质矿产勘查开发局106地质队,四川温江611130

出　　处：《矿物岩石》2014年第1期46-51,共6页Mineralogy and Petrology

基　　金：中国地质调查局项目青藏高原中部羌塘-藏东地体构架及碰撞造山(1212011121271);国土资源部构造成矿成藏实验室开放式基金(gzck20130006);构造成矿学理论发展与实践团队基金(13TD0008)

摘　　要：安多白垩系上统马登火山岩（K。md）出露于班公湖一怒江缝合带中段。对马登火山岩的岩石学和地球化学研究表明，火山岩属低钾钙碱性和钙碱性系列，主量元素以富A1203（14．40％～17．70％）、低MgO（0．31％～l.36％）、低Ti02（0．33％～0．68％）、贫K20（O．74％～1．95％）、Na。O〉K。O为特征。安多马登火山岩稀土总量较高，约96．15×10-6～126．05×10-6，无Eu异常（8Eu=0．80～l.20，平均0．96）。分配型式属于轻稀土富集型（LREE／HREE一7．88～1l.12，平均9．51）。微量元素相对富集Rb，U，K，Hf，Zr，La和Ce；相对亏损Ba，sr，Nb，P，Ta和Ti。亏损高场强元素Nb，P，Ta和Ti，具有典型岛弧火山岩特征。常量微量元素地球化学特征研究表明马登火山岩最有可能来源于下地壳部分熔融。结合地质背景和构造环境判别图解综合分析，安多马登火山岩形成于大陆岛弧构造环境，是与班公湖一怒江特提斯洋向北向南双向俯冲的产物。Madeng volcanic rocks exposed in Anduo area in the middle of Bangongco-Nujiang su- ture zone belong to low-K calc-alkaline and calc-alkaline series based on the analysis of their ma- jor,REE element and rear element compositions. In fact,the major elements of the volcanic rocks are characterized by high A12Oa （14. 400//00 17.70%）, poor TiO2 （0.33% 0.68%//00）, poor MgO （0.31%1.36%） and K20（0.74%1.95%）,with Na20〉 K20. These volcanic rocks have high content of Y.REE, no Eu anomaly （Eu=0. 801.20,with a mean value of 0.96） ,and Chondrite- normalized REE diagrams show LREE-enriched patterns （LREE/HREE = 7.88 11.12, avera- ging 9.51）. Trace elements are enriched in Rb,U,K,Hf,Zr,La and Ce,depleted in Rb,K,Nb,P, Ti and depleted in high-field strength elements （Nb.P.Ta and Ti）,showing essential characteris- tics of subduction-related arc volcanic rocks. The major and tracer element geochemistry indicate that the Madeng volcanic rocks are likely derived from the partial melting of lower crust. Com- bined with the geological setting and tectonic discrimination,it is considered that the Madeng vol- canic rocks are most likely related to the bidirectional subduction （southward subduction and northward subduction） of Bangongco-Nujiang suture zone.

关 键 词：火山岩 地球化学特征 双向俯冲 安多 

分 类 号：P588.14[天文地球—岩石学] P595[天文地球—地质学]