西藏狮泉河蛇绿混杂岩中枕状熔岩锆石LA-ICP-MS U-Pb测年、岩石地球化学特征及构造意义  

LA-ICP-MS zircon U-Pb dating and geochemistry of pillow lava in Shiquan River ophiolitic mélange zone and the tectonic significance

作　　者：龚福志 魏铭 宁建胜 秦松楠 旦增西绕 GONG Fuzhi;WEI Ming;NING Jiansheng;QIN Songlan;TENZIN Thyrab(No.2 Geological Party of Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850000,Tibet,China)

机构地区：[1]西藏自治区地勘局第二地质大队,拉萨850000

出　　处：《地质找矿论丛》2025年第1期83-92,共10页Contributions to Geology and Mineral Resources Research

基　　金：中国地质调查局项目(编号:121201233000160040)子项目的资助。

摘　　要：对狮泉河蛇绿混杂岩中枕状熔岩进行了年代学、元素地球化学研究。用LA-ICP-MS技术测得安山质枕状熔岩锆石U-Pb年龄为125.3 Ma±3.3 Ma,为早白垩世中期。岩石具枕状构造和球颗结构;地球化学特征显示,岩石具有较高的SiO_(2)、MgO含量,而Al_(2)O_(3)、K_(2)O、TiO_(2)含量则相对较低,属准铝质富钠贫钾钙碱性岩石;所有测试样品的REE含量较低,轻、重稀土分馏不明显,Eu元素无异常;相对富集Rb、K、Ba、Sr等大离子亲石元素及高场强元素Th、U、Hf、Pb等,相对亏损Nb、Zr、P、Ti等,在稀土元素球粒陨石标准化配分图和原始地幔蛛网图中图式与富集型大洋中脊玄武岩E-MORB相似。研究表明,枕状熔岩可能形成于弧后盆地富集型大洋中脊环境,由此认为,狮泉河一带在早白垩世中期仍处于弧后盆地的深海环境,为研究狮泉河永珠嘉黎蛇绿混杂岩带的演化历史提供了直接的火山岩证据。This paper deals with Chronology and element geochemistry of the pillow lava.LA-ICP-MS zircon U-Pb age dating of the lava is 125.3 Ma±3.3 Ma corresponding to the middle of Cretaceous Period.Geochemistry of the lava is characterized by typical metaluminous calc-alaliine serial rocks with high Na and low K content;all analysis of samples collected by relatively high SiO_(2) and MgO,relatively low Al_(2)O_(3),K_(2)O and TiO_(2),no obvious fractionation of LREE and HREE and Eu anomaly;relative enrichment of LILEs(Rb,K,Bs,Sr)and HFSE(Th,U,Hf,Pb etc.)and relative depletion of Nb,Zr,Ti etc.The data mentioned above and the chondrite-normalized REE pattern and primitive mantle-normalized spider diagram of the pillow lava are all similar to E-MORB(enriched middle ocean ridge basalt).Therefore,the pillow lava may be formed in deep water environment of back-arc basin during the middle of Early Cretaceous Period.Results of the paper will provide direct evidence for studying evolution history of Shiquan River ophiolitic mélange belt.

关 键 词：狮泉河蛇绿混杂岩 枕状熔岩 早白垩世中期 弧后盆地中E-MORB 西藏 

分 类 号：P588.36[天文地球—岩石学] P597[天文地球—地质学]