藏北羌塘冈玛错地区望果山组火山岩地球化学特征及LA-ICP-MS锆石U-Pb年龄  

Geochemistry and LA-ICP-MS zircon U-Pb age of volcanic rocks of Wangguoshan Formation in the Gangmar Co area of Qiangtang, Tibet

作　　者：江庆源 李才[1] 解超明[1] 王明[1] 胡培远[1] 吴浩[1] 彭虎[1] 陈景文[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《地质通报》2014年第11期1702-1714,共13页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41272240;41072166);中国地质调查局项目(编号:1212011221093;12120113036700)

摘　　要：羌塘中部冈玛错地区厘定出一套早石炭世火山岩，该火山岩为一套酸性-基性岩（流纹岩、英安岩、安山岩、玄武安山岩、玄武岩等）夹火山碎屑岩的岩石组合。2件定年样品（英安岩和安山岩）的LA-ICP-MS锆石U-Pb年龄分别为358.2Ma±1.2Ma和350.5Ma±1.4Ma，时代为早石炭世，代表了该火山岩的形成年龄。岩石地球化学特征显示，该火山岩的铝饱和指数A/CNK值为0.62~1.08，平均值为0.81；里特曼指数δ为1.04~2.67，平均值为1.84；大离子亲石元素（LILE）Th、U、Pb明显富集，高场强元素（HFSE）Nb、Ta、Ti亏损，反应了偏铝质钙碱性岛弧火山岩的特征。由此说明，在早石炭世龙木错-双湖-澜沧江洋已经进入俯冲消减阶段。A set of early carboniferous volcanic rocks has been found in the Gangmar Co area of Qiangtang for the first time. The volcanic rocks are composed of acidic to basic volcanic rocks （rhyolite, dacite, basaltic andesite, basalt and andesite） intercalated with pyroclastic rocks. The LA-ICP-MS zircon U-Pb ages of two samples （dacite and basaltic andesite） are 358.2Ma±1.2Ma and 350.5Ma± 1.4Ma, which indicates that the volcanic rocks formed in the early Carboniferous. Rock geochemical characteristics show that the A/CNK indexes are 0.62~1.08, with an average of 0.81, and Rittmann indexes （δ） are 1.04~2.67, with an average of 1.84. These volcanic rocks are characterized by high LILE （Th, U and Pb） and obvious depletion of HFSE （Nb, Ta and Ti）. The geochemical compositions of volcanic rocks belong to the calc-alkaline island arc volcanic rocks. It is indicated that the Lungmu Co-Shuanghu-Lancang River Ocean entered into its subduction stage in the Early Carboniferous.

关 键 词：青藏高原 早石炭世 岛弧火山岩 LA-ICP-MS锆石U-PB年龄 地球化学 

分 类 号：P588.1[天文地球—岩石学] P595[天文地球—地质学]