青海治多地区多彩蛇绿混杂岩带南侧当江荣二叠纪—三叠纪岩浆弧的确定  

The define and geological significance of Permian-Triassic magmatic arc at Dangjiangrong,south of Duocai ophiolite mélange zone in the Zhiduo area,Qinhai,China.

作　　者：刘银[1,2] 李荣社[2] 计文化[2] 潘术娟[1,2] 时超[1,2] 陈奋宁[2] 陈守建[2] 赵振明[2] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质调查局西安地质矿产研究所,陕西西安710054

出　　处：《地质通报》2010年第12期1840-1850,共11页Geological Bulletin of China

基　　金：中国地质调查局项目<青藏高原前寒武纪地质和古生代构造-古地理综合研究>(编号:1212010610102);国家自然科学基金项目<青藏高原中北部地区中上二叠统不整合地质意义研究>(编号:40872084)资助

摘　　要：在多彩蛇绿混杂岩带南侧当江荣火山岩带测制了一条近S—N向的剖面,通过野外对剖面出露的火山岩的详细观察,其组合有:安山岩-流纹斑岩-流纹质凝灰岩-安山质凝灰熔岩,对其系统采样并进行了XRF岩石化学分析和ICP-MS微量、稀土元素分析。结果表明,该套火山岩为高Si(SiO2平均为66.76%)、低Ti(TiO2平均为0.41%)和富Na(Na2O>K2O)的钙碱性系列岩石(里特曼指数σ=0.51～1.99<3.3);富集LILE元素(Rb、Ba等),亏损HFSE元素(Nb、Ta等)和P、Ti等元素;稀土元素总量较低(ΣREE=72.43×10-6～141.16×10-6),轻重稀土元素分馏较强(ΣLREE/ΣHREE=1.46～3.28),稀土元素分配模式为轻稀土富集型,轻度的Eu负异常(δEu=0.58～0.89)。主量、稀土、微量元素相关判别图解均指示其为典型的钙碱性系列岩石组合,属于与板块俯冲作用有关的岩浆岛弧带的产物,从而为多彩沟蛇绿混杂岩带的俯冲极性和构造环境的进一步确定提供了新的佐证。Duocai ophiolite mélange zone,a part of the Xijir Ulan lake-Jinsha river ophiolite zone,located in the binding site of jinsha suture zone and ganzi suture belt of the northern Tibet Plateau.Through the detailed field investigation of the S-N directional cross section of Dangjiangrong volcanic rocks zone,located in the south of the Duocai ophiolite meglange zone,we found that the pre-existed main rock assemblage was andesite,rhyolite porphyry,rhyolitic tuff and andesitic tuffaceous lava.The results from XRF analysis and ICP-MS analysis on systemic sampling show that the Dangjiangrong volcanic rocks are rich in SiO2（56.92%~75.71%） and Na2O（Na2OK2O）,poor in TiO2（0.15%~0.77%）,belonging to calc-alkaline type rocks.The chondrite-normalized REE-patterns are characterized by LREE enrichment with variable degree of negative Eu anomalous values（δEu=0.58~0.89） and the primary mantle-normalized trace elements-parterns by HFSE depleted as well as P element.It is proved that the volcanic rocks were formed in an island-arc environment by the evidence of petrochemistry and geochemistry of trace and rare element,which provides the corroborating evidences to the further define of subduction polarity and tectonic setting of Duocai ophiolite mélange zone.

关 键 词：青海治多地区 多彩蛇绿混杂岩 岩浆弧 地球化学 构造环境 地质意义 

分 类 号：P588.13[天文地球—岩石学] P588.21[天文地球—地质学]