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北祁连山扎麻什地区东沟蛇绿岩LA-ICP-MS锆石U-Pb测年及其地球化学特征
引用本文:武鹏,李向民,徐学义,余吉远,孙吉明,唐卓,王国强.北祁连山扎麻什地区东沟蛇绿岩LA-ICP-MS锆石U-Pb测年及其地球化学特征[J].地质通报,2012,31(6):896-906.
作者姓名:武鹏  李向民  徐学义  余吉远  孙吉明  唐卓  王国强
作者单位:1. 中国地质调查局西安地质调查中心,陕西 西安,710054
2. 中国地质调查局西安地质调查中心,陕西 西安 710054;长安大学地球科学与资源学院,陕西 西安 710064
基金项目:中国地质调查局青藏专项
摘    要:东沟蛇绿岩位于北祁连造山带中东段的扎麻什一带,主要由辉橄岩、辉长岩和基性火山岩组成较为完整的蛇绿岩单元。对基性火山岩进行单颗粒锆石LA-ICP-MS U-Pb同位素测定,获得499.3Ma±6.2Ma年龄加权平均值,代表蛇绿岩的形成年龄,相当于晚寒武世。岩石地球化学研究表明,该蛇绿岩中的基性火山岩属于拉斑玄武岩系列,球粒陨石标准化稀土元素分配模式为近平坦型,(La/Yb)N在0.97~1.26之间;微量元素分配模式除个别大离子亲石元素(Ba、Rb、U、K)外基本为平坦型曲线,Nb、Ta、Zr、Hf无亏损,显示出洋中脊玄武岩(N-MORB)的地球化学特征;在Zr-Zr/Y和Ti/100-Zr-3Y等构造环境判别图中,所有样品数据点均落入MORB区域内,表明其形成于洋中脊环境。经区域对比,该蛇绿岩与玉石沟、川刺沟蛇绿岩等一起构成了大洋扩张脊型蛇绿岩带。

关 键 词:LA-ICP-MS锆石U-Pb测年  东沟蛇绿岩  洋中脊环境  北祁连造山带

LA-ICP-MS zircon U-Pb dating and geochemical characteristics of Donggou ophiolites in Zamashi area of northern Qilian Mountain
WU Peng , LI Xiang-min , XU Xue-yi , YU Ji-yuan , SUN Ji-ming , TANG Zhuo , WANG Guo-qiang.LA-ICP-MS zircon U-Pb dating and geochemical characteristics of Donggou ophiolites in Zamashi area of northern Qilian Mountain[J].Geologcal Bulletin OF China,2012,31(6):896-906.
Authors:WU Peng  LI Xiang-min  XU Xue-yi  YU Ji-yuan  SUN Ji-ming  TANG Zhuo  WANG Guo-qiang
Institution:1,2 1.Xi′an Institute of Geology and Mineral Resources,China Geological Survey,Xi′an 710054,Shaanxi,China; 2.College of Earth Science and Land Resources,Chang’an University,Xi′an 710064,Shaanxi,China
Abstract:Donggou ophiolite occurs in Zamashi area along the eastern segment of northern Qilian orogenic belt. The ophiolite is mainly composed of pyroxene peridotite, gabbro and mafic volcanic rocks, making up a relatively complete ophiolite unit. Single-grain zircon LA-ICP-MS U-Pb isotopic dating of mafic volcanic rocks yielded a weighted average age of 499.3±6.2 Ma, which represents the ophiolite formation age, equivalent to Late Cambrian. According to geochemical studies, the ophiolite mafic volcanic rocks are of tholeiitic series, the chondrite-normalized REE patterns are nearly of flat-type; the (La/Yb)N ratios are between 0.97 and 1.26; the trace element distribution patterns basically show flat curves with the exception of a few large-ion lithophile elements (Ba, Rb, U, K); Nb, Ta, Zr, Hf have not experienced loss, suggesting geochemical characteristics of mid-ocean ridge basalt (N-MORB); in Zr-Zr/Y and Ti/100-Zr-3Y tectonic discrimination diagrams, all the samples fall into the MORB area formed in mid-ocean ridge. A comparative study of the region shows that the ophiolite and Yushigou as well as Cuancigou ophiolite jointly constitute the spreading ridge-type ocean ophiolite.
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