南祁连野牛脊山地区早志留世侵入岩的岩石成因:岩石地球化学和锆石LA-ICP-MS U-Pb年代学制约  

Petrogenesis of Early Silurian Intrusive Rocks in Yeniujishan Area of South Qilian:Constraints from Geochemistry and LA-ICP-MS Zircon U-Pb Geochronology

作　　者：于小亮 蔡成龙 张世龙 魏小林 刘溪溪 YU Xiaoliang;CAI Chenglong;ZHANG Shilong;WEI Xiaolin;LIU Xixi(Qinghai Geological Survey,Xining 810001,Qinghai,China;No 7 Geological Brigade,Qinghai Provincial Bureau of Nonferrous Metal and Geological Exploration,Xining 810007,Qinghai,China;Qaidam Synthetical Exploration Institute of Geology and Mineral Resources of Qinghai Province,Geermu 816000,Qinghai,China)

机构地区：[1]青海省地质调查局,青海西宁810001 [2]青海省有色地质矿产勘查局七队,青海西宁810007 [3]青海省柴达木综合地质矿产勘查院,青海格尔木816000

出　　处：《西北地质》2018年第4期133-146,共14页Northwestern Geology

基　　金：中国地质调查局"柴达木周缘及邻区成矿带地质矿产调查评价"(1212011221151)

摘　　要：对南祁连野牛脊山地区侵入岩进行了岩石地球化学和锆石LA-ICP-MS U-Pb年代学研究,进而约束其岩石成因和形成的构造背景。该地区侵入岩主要岩性为花岗闪长岩、似斑状花岗闪长岩和似斑状二长花岗岩。地球化学特征显示:岩石具有高硅、富铝、富钾、富碱和贫钛、铁、镁、钙的特征,其w(SiO_2)=64.69%～78.03%,w(Al_2O_3)=7.44%～14.16%,w(K_2O)=2.98%～5.23%,w(Na_2O+K_2O)=5.13%～7.92%,(TiO_2)=0.55%～0.94%,w(FeO)=1.52%～5.00%,w(CaO)=1.11%～3.43%,w(MgO)=0.78%～2.49%,岩石里特曼指数δ=0.91～2.89,A/CNK为0.84～1.23,为准铝质-弱过铝质的钙碱性系列岩石。岩石稀土元素总含量量较低(ΣREE为157.89×10^(-6)～299.15×10^(-6)),相对富集轻稀土元素、大离子亲石元素(Rb、K)和Th,亏损重稀土元素,Ba,Ce、Hf、Zr、Sm、Y、Yb等明显低于洋脊花岗岩,具有明显的Eu负异常(δEu=0.47～0.66)。综合地质地球化学资料,显示该侵入岩属于S型花岗岩且来源于地壳物质的重熔。由w(Y)-w(Nb)图解和R1-R2构造环境判别图解可得知研究区内花岗岩与南祁连造山带板块碰撞有关。在似斑状花岗闪长岩中获得LA-ICP-MS锆石U-Pb年龄为(443.9±2.1)Ma,侵位时代为早志留世。结合区域构造演化分析,认为野牛脊山地区侵入岩形成于板块俯冲碰撞的地球动力学背景下。In order to to constrain its petrogenetic and tectonic processes, the geochemistry and LA ICP MS zircon U Pb dating of intrusive rocks from Yeniujishan area in South Qilian has been conducted in this paper. The intrusive rocks in this area are mainly composed of granodior 0.91 to 2.89, while their aluminum saturation index （A/CNK） vary from 0.84 to 1.23, belong ing to the calc alkaline series, with the characteristics of metaluminous weakly peraluminous rocks. These rocks have low EREEvalues （157.89X10 6~299.15X10 6）, which are relatively enriched in LREE, large ion lithophile elements （Rb, K） and Th element. But, they are relative ly depleted in HREE, while their Ce, Hf, Zr, Sin, Y and Yb values are obviously lower than the ones of mid ocean ridge granitoids, with strong negative Eu anomaly （3Eu 0.47~0.66） . The geological and geochemical data suggest that these intrusive rocks are S type granite, which was formed by the re melting of crustal material. The discrimination diagrams for tectonic set tings （ω （Y） ω （Nb） and R1 R2） show that these granites are related to the plate collision of South Qilian orogenic belt. The U Pb dating of porphyritic granodiorite yields an age of （443.9＋2.1） Ma, indicting that these rocks were emplaced in Early Silurian. In combination with the comprehensive analysis of tectonic evolution, it is believed that these intrusive rocks in Yeniujishan area formed under the geodynamic background of subduction collision.

关 键 词：早志留世 花岗岩 地球化学 锆石U-Pb年代学 野牛脊山 南祁连 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]