青海阿木尼克山地区牦牛山组火山岩地球化学特征、锆石U-Pb年龄及其地质意义

发布时间：2018-01-29 02:19

本文关键词： 牦牛山组火山岩地球化学特征构造事件 LA-ICP-MS锆石U-Pb测年　出处：《地质通报》2017年Z1期 　论文类型：期刊论文

【摘要】：利用岩石地球化学分析和LA-ICP-MS锆石U-Pb定年方法,对阿木尼克山地区牦牛组火山岩进行了系统的地球化学特征和锆石U-Pb年代学研究。其地球化学特征为,SiO_2含量介于53.94%~64.69%之间,全碱含量介于5.38%~9.86%之间,范围较大,里特曼指数介于1.45~4.54之间,属于碱性岩和钙碱性岩,铝饱和指数A/CNK均大于1.1,具有S型花岗岩的特征;稀土元素总量为68×10~(-6)~372×10~(-6),LREE/HREE值介于4.51~18.25之间,轻稀土元素富集,重稀土元素亏损,稀土元素配分曲线右倾;微量元素中不相容元素Rb、Ba、Th富集,Ta、Nb亏损明显,蛛网曲线呈现峰谷迭起的曲线形式。锆石CL图像和U-Pb同位素分析结果显示,牦牛山组火山岩锆石自形程度好,均有岩浆振荡环带的特征,Th/U值介于0.4~1.3之间,属于岩浆成因锆石。测得该火山岩中2件样品的锆石~(206)Pb/~(238)U年龄介于371~399Ma之间,年龄加权平均值分别为374.8±3.1Ma和392.4±3.3Ma,表明火山岩形成时代为中—晚泥盆世。结合区域特征,认为牦牛山组火山岩的形成与柴达木盆地北缘的演化有关,其是后碰撞阶段伸展作用的产物。
[Abstract]:Geochemistry analysis and LA-ICP-MS zircon U-Pb dating method are used. The geochemical characteristics and zircon U-Pb chronology of the yak volcanic rocks in the Amunicia Mountain area have been systematically studied. The geochemical characteristics of the volcanic rocks are as follows. The content of SiO_2 was between 53.94 and 64.69%, and the content of total alkali was between 5.384.86% and 9.86%, and the Ritman index was between 1.45 and 4.54. It belongs to alkaline rock and calc-alkaline rock, and the Al saturation index A / CNK is higher than 1.1, which is characterized by S-type granite. The total amount of rare earth elements is 68 脳 10 ~ (10) ~ (-6) ~ (6) ~ 372 脳 10 ~ (10) ~ (-1) ~ (-1) LREE / HREE = 4.51 ~ 18.25, which is enriched in light rare earth elements. Loss of heavy rare earth elements, right deviation of the distribution curve of rare earth elements; The enrichment of Th in trace element RbsBaTh is characterized by obvious depletion of Th, and the curve of cobweb appears to be a curve with peaks and valleys. The results of CL zircon images and U-Pb isotopic analysis show that the trace elements are depleted. The zircon of the volcanic rocks of the Yaniushan formation is of good shape, and the characteristics of the magmatic oscillating ring zone range from 0.4 to 1.3. Zircon of magmatic origin. Two samples of zircon from this volcanic rock were measured, and the ages of zircon / Zircon / B / B / B _ (238U) are between 371- 399Ma and 371m ~ 399Ma. The average age weighted values are 374.8 卤3.1 Ma and 392.4 卤3.3 Ma, respectively, indicating that the volcanic rocks were formed in the Middle to late Devonian epoch and combined with regional characteristics. It is considered that the formation of volcanic rocks in Yaniushan formation is related to the evolution of the northern margin of the Qaidam basin and is the product of extension in the post-collision stage.
【作者单位】：成都理工大学地球科学学院;
【基金】：中国地质调查局项目《柴达木周缘及邻区成矿带地质矿产调查评价》下属研究项目《青海省都兰县阿木尼克山地区J47E017001、J47E018001、J47E018002、J47E019003四幅1∶5万区域地质矿产调查》(编号:1212011221146)
【分类号】：P588.14
【正文快照】： 青海省地矿局石油普查大队1962年在《祁连山、阿尔金山、昆仑山地质概况》[1]一书中于柴达木盆地东北缘创名“牦牛山统”。原义指“系盆地东北缘牦牛山一带,由紫红色砾岩、砂岩、泥板岩、火山岩组成”。牦牛山统上部与石炭系为不整合接触,下与地槽相的奥陶系不整合接触,产植物

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