内蒙古锡林浩特毛登牧场早石炭世花岗岩锆石U-Pb年龄、地球化学特征及其地质意义  

Zircon U-Pb Dating and Geochemistry of Granites in Early Carboniferous in Maodeng of Xilin Hot,Inner Mongolia and Their Geological Implications

作　　者：袁建国[1] 任永健[2] 姜振宁[2] 屈云燕 魏浩 YUAN Jianguo;REN Yongjian;JIANG Zhenning;QU Yunyan;WEI Hao(School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;Geological Institute, China Chemical Geology and Mine Bureau, Baoding, Hebei 072750, China;General Institute of Chemical Geology Survey, China Chemical Geology and Mine Bureau, Beijing 100013, China;School of Nature Resource, Hebei GEO University, Shijiazhuang, Hebei 050031, China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中化地质矿山总局地质研究院,河北保定072750 [3]中化地质矿山总局化工地质调查总院,北京100013 [4]河北地质大学资源学院,河北石家庄050031

出　　处：《现代地质》2017年第6期1131-1146,共16页Geoscience

基　　金：中国地质调查局地质调查工作项目(1212011220449)

摘　　要：通过对内蒙古锡林浩特毛登牧场早石炭世花岗岩体进行野外观察、LA-ICP-MS锆石U-Pb测年以及地球化学测试,讨论其构造环境,进一步为研究古亚洲洋闭合时限提供依据。测年结果表明:花岗闪长岩为(330.6±1.8)Ma,二长花岗岩为(327.7±2.6)Ma,成岩时代为早石炭世。岩石地球化学分析表明:花岗闪长岩为强过铝质、钙碱性系列岩石,具有活动大陆边缘的亲缘性特征。微量元素特征指示花岗闪长岩具有典型下地壳来源特征并伴有部分幔源岩浆混合作用,为弧岩浆岩。二长花岗岩为具高硅、富碱、相对低铝特征的高钾钙碱性系列岩石。两类差异明显的岩石稀土配分曲线表明二长花岗岩具有下地壳岩浆重熔的演化特征。微量元素特征指示样品为大陆弧环境下壳源重熔的成熟弧花岗岩。构造判别图显示花岗闪长岩为代表活动大陆边缘环境的I型花岗岩,而二长花岗岩则为指示活动大陆边缘弧后伸展环境的A2型花岗岩,二者构成I-A型复合岩体,说明研究区在早石炭世仍存在古亚洲洋向西伯利亚板块的俯冲作用,推测古亚洲洋此时尚未闭合。In this paper, a series of analyses including field observation, LA-ICP-MS zircon U-Pb isotopic dat- ing, major element and trace element were performed on the granites in Early Carboniferous in Maodeng of Xilin Hot, Inner Mongolia in order to make the discussion of tectonic environment of the study area. Two types of granites were identified which of granodiorite and monzonite granite are invaded into the former. The result of the LA-ICP-MS zircon U-Pb isotopic dating are （330. 6 ± 1.8） Ma for granodiorite and （ 327.7 ± 2.6 ） Ma for monzonite granite, which suggests that the granites formed in the Early Carboniferous. The geochemical feature of major elements in the granodiorite is strongly peraluminous （ A/CNK = 1.32） and of calcium-alkali. The pat- tern of LREE enrichment type indicates the active continental margin environment with the feature of low REE （67.65 × 10^-6）, （La/Yb）N（ 8.37 ） and slight negative anomaly. The trace element geochemistry shows evi-dent enrichment of LILE（Rb, Ba, Sr）, heat producing element（Th, U, K） and HFSE（Zr, Hf） with strong deficit of Nb, P and Ti, which imply that the samples are arc magmatic suites coming from the lower crust with few mantle-derived magma. The geochemical feature of major elements in the monzonite granites is of high SiO2 （75.85%） and K20 ＋ Na20（8.54% ）, low A1203 relatively, which belongs to weak peraluminous（A/CNK = 1.01 ） series and high-K calc-alkali series. The feature of REE are divided into two types. One type is of high REE （ 120. 28 × 10^-6 ） with negative Eu anomalies （0. 88 ）, LREE/HREE （ 4. 96 ）, （La/Yb） N （ 10. 09 ）, which shows the strong differentiation between the HREE and LREE. The patterns of the other type granites show the slightly differentiation like the ＂sea gull＂ with low REE（54. 28 x 10-6）, strong Eu negative anor- malies （0.27）, LREE/HREE （1.99）, （La/Yb）N（1.50）, which comes from the remelting of the low crust. The trace element geochemis

关 键 词：I-A型花岗岩 LA-ICP-MS锆石U-PB测年 活动陆缘环境 古亚洲洋 锡林浩特 

分 类 号：P588.1[天文地球—岩石学] P597[天文地球—地质学]