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。
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.Singlegrain 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.
出处
《地质通报》
CAS
CSCD
北大核心
2012年第6期896-906,共11页
Geological Bulletin of China
基金
中国地质调查局青藏专项<北祁连成矿带成矿条件研究与找矿靶区优选>(编号:1212010818090)
