国庆钨矿钾长花岗岩年代学、地球化学特征及其地质意义  

Chronology and geochemical characteristics of K-feldspar granite in the Guoqing tungsten deposit and their geological implications

作　　者：李鹏[1,2] 吕新彪[1,2] 陈超[1,2] 曹晓峰[1,2] 玛依拉.艾山 苏妤芸[1,2] 

机构地区：[1]中国地质大学资源学院 [2]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《岩石矿物学杂志》2011年第1期13-24,共12页Acta Petrologica et Mineralogica

基　　金："十一五"国家科技支撑计划重点资助项目(2007BA25B04)

摘　　要：国庆钾长花岗岩岩体出露于蒙古自治区额济纳旗西南部的盘陀山一带,北邻牛圈子-洗肠井缝合带,LA-ICP-MS测得该岩体的U-Pb年龄为439.1±8Ma。岩体SiO2含量73.31%～74.36%,A/CNK>1.1,K2O/Na2O=1.25～1.40,里特曼指数介于2.06～2.22之间,属于高钾钙碱性、过铝质花岗岩系列,岩体富集大离子亲石元素,亏损高场强元素。稀土和微量元素分析显示钾长花岗岩总体轻稀土元素富集,轻、重稀土元素分馏较低,具有较明显Eu负异常(δEu=0.65～0.77),具K、Rb、Ba、Th等元素富集,Nb、Ce、Zr、Hf、Sm、Y、Yb等元素亏损的特征。综合分析表明,国庆钾长花岗岩为壳源S型同碰撞花岗岩;结合区域构造演化历史,认为国庆钾长花岗岩为古老地壳物质重熔形成,是早志留世月牙山-洗肠井古洋盆闭合同碰撞阶段的产物。同时对该区志留—泥盆纪碰撞伸展环境下成矿前景初步分析,为矿床研究和区域矿产预测工作提供参考。Located near Pantuoshan district in Ejina Banner of southwestern Mongolia, Guoqing K-feldspar granite body lies in southern Niujuanzi-Xichangjing suture zone. LA-ICP-MS U-Pb isotopic dating of zircon separated form the rock yields an average weighted 2~6pb/238U age of 439.1 ± 8 Ma. The results of geochemical study indicate that SiOa are in the range of 73.31% -- 74.36 %, A/CNK 〉 1.1, and K20/Na20 = 1.25 -- 1.40, the Rittmann index of k-feldspar granite varies from 2.06 to 2.22, suggesting a high-K calc-alkaline series and peraluminous nature. The results also indicate that Guoqing K-feldspar granite body is highly enriched in large ion lithophile elements and strongly depleted in high field strength elements. The chondrite-normalized REE and trace elements patterns demonstrate low fractionation level between LREE and HREE, （La/Yb）N = 3.40 5.44, and negative Eu（δEu= 0. 65- 0.77）, which might have been related to the plagioclase residuals during the partial melt of the original rock. The spider diagrams are characterized by Nb, Ce, Zr, Hf, Sm, Y, Yb depletion and K, Rb, Ba, Th enrichment. Rb/Sr ratios are between 4.37 and 4.70, and such high Rb/Sr ratios （ 〉2 ） suggest that Guoqing granite body was probably triggered by dehydration melting of mica duringthe geological process. High levels of Nb and Ta and characteristics of Ta〉Nb indicate high-degree evolution of the granite body, which laid the foundation of tungsten elements enrichment. CaO/Na2O ratios range from 0.152 to 0. 165, and all the values are lower than 0.3, suggesting the origination from re-melting of the early Precambrian crystalline basement. In addition, the inherited zircon in the granite body yields a large number of ages between 616 Ma and 1 046 Ma. In Hongliuhe area, the zircon U-Pb age of granite that intruded into ophio- lite is 404.8± 5.2 Ma, implying that the muth Tianshan oceanic crust was formed as early as Early Cambrian, and closed before Emsian. In Xichangjing area, the closure of South Tianshan Ocean was before 43

关 键 词：钾长花岗岩 同碰撞 国庆钨矿 内蒙古北山 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]