蒙古巴音苏赫图钨矿床正长斑岩锆石U-Pb年龄及其地质意义  

Zircon U-Pb Ages and Its Significance of the Syenite Porphyry in Bayinsuhetu Tungsten Deposit,Mongolia

作　　者：郭志华 张宝林[2] 党永岐 郭勃巍 高磊 侯金亮 张丽春 

机构地区：[1]华北理工大学矿业工程学院地质系,河北唐山063009 [2]中国科学院地质与地球物理研究所矿产资源研究重点实验室,北京100029 [3]河北省地矿局第五地质大队,河北唐山063000 [4]造山带与地壳演化教育部重点实验室北京大学地球与空间科学学院,北京100871

出　　处：《地质论评》2017年第5期1378-1390,共13页Geological Review

基　　金："十一五"科技支撑计划重大项目(编号:2006BAB01A02);校级博士科研启动基金项目(编号:20164043)的成果~~

摘　　要：正长斑岩是中蒙边界中生代重要的岩浆记录,其花岗岩年龄和地球化学特征对于揭示该时期的构造格局与演化历史具有重要意义。本文对蒙古国东南部出露的正长斑岩进行锆石的LA-ICP-MS定年,获得锆石U-Pb年龄为(170.6±1.7)Ma,表明该花岗岩形成于中—晚侏罗世。花岗岩的元素地球化学研究结果表明:该花岗岩属高钾钙碱性S型花岗岩;花岗岩具高硅特征,其Si O2质量分数为73.99%~74.28%,Al_2O_3为12.36%~14.30%,MgO为0.17%~0.45%,过铝质;稀土元素总量为51.92×10^(-6)~58.32×10^(-6),稀土元素分布型式为具有明显负铕异常的"燕型"曲线;在原始地幔标准化的微量元素蛛网图中,Rb、Th、U、K、Zr、Hf和轻稀土元素(如La、Ce、Nd和Sm等)富集,Ba、Sr、P和Ti等元素强烈亏损,Nb和Ta具有中等—弱亏损特点;n(^(143)Nd)/n(^(144)Nd)初始比值较高(0.512320~0.512451),平均为0.512404;ε_(Nd)(t)为-4.6^-2.3,均为负值。主量、微量元素和同位素特征表明,该正长斑岩形成于同碰撞向后造山构造体制转换过渡的伸展大地构造环境背景之下。地壳加厚作用和地壳物质部分熔融,很可能是形成本区花岗岩的两个最主要的动力机制。Objectives：The syenite porphyry is an important magmatism record of China—Mongolia border region in the period of Mesozoic Era. The formation age and geochemical characteristics of the adamellite are significant to reveal the tectonic framework and evolution history at that period. Methods： Samples were crushed into granules of less than 200 mesh and then analyzed for major and trace elements. All analyses were conducted at the IGG’s State Key Laboratory of Lithospheric Evolution in Beijing, China. Major elements were determined by x ray fluorescence spectrometry on fused glass disks using an Axios mineral separation tool, with analytical uncertainties ranging from 1% to 5%. Trace element and rare earth element concentrations were determined by ICP MS with an ELEMENT system. According to Chinese national standards GSR 1 and GSR 2, the error was 〈5% for trace elements with concentrations of 10×10-6 and 〈10% for trace elements with concentrations of 〈10×10-6. Zircon LA ICP MS U Pb isotope analyses were performed at the Chinese Academy of Geological Sciences using a laser ablation system （193 nanometers （nm）, GeoLas 200M） coupled to a Neptune （Thermo Fisher） Multicollector Inductively Coupled Plasma Mass Spectrometer （MC ICP MS）. Zircon U Th Pb measurements were made on 32 nm diameter spots on single grains. NIST 612 was used as an internal standard for U, Th, and Pb analyses and zircon GJ 1 was used as the external calibration standard. Common lead was corrected using the method of Andersen （2002）. Isotopic ratios and element concentrations were calculated using the ICP MS Data Cal software. Ages were calculated using ISOPLOT 3. Results： The granite was formed in the Middle—Late Jurassic period and the U Pb age of zircon is 170.6±17 Ma. The geochemical data of granite show that it is high K calc alkaline. Also the granite is characterized with high silicon, with SiO2 （7399%～7428%）, A12O3 （1236%~1430

关 键 词：蒙古国 正长斑岩 锆石U-PB年龄 地球化学 构造意义 

分 类 号：P597.3[天文地球—地球化学] P618.67[天文地球—地质学]