内蒙古克什克腾旗长岭子斜长花岗斑岩锆石U-Pb年龄、成因与碰撞造山作用  

Zirzon U-Pb age and petrogenisis of plagiogranite porphyry in Changlingzi,Hexigten Banner,Inner Mongolia and its collision orogeny

作　　者：许强伟 王玭 王志强[3] 王成明 郑义 方京 XU Qiangwei;WANG Pin;WANG Zhiqiang;WANG Chengming;ZHENG Yi;FANG Jing(School of Earth and Space Science,Peking University,Beijing 100871,China;Key Laboratory of Marginal Sea Geology,South China Sea Institute of Oceanology,Chinese Academy of Sciences,Guangzhou 510301,Guangdong,China;School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,Anhui,China;School of Earth Sciences and Geological Engineering,Sun Yat-sen University,Guangzhou 510275,Guangdong,China;Institute of Deep-Sea Science and Engineering,Chinese Academy of Sciences,Sanya 572000,Hainan,China)

机构地区：[1]北京大学地球与空间科学学院,北京100871 [2]中国科学院边缘海与大洋地质重点实验室南海海洋研究所,广东广州510301 [3]合肥工业大学资源与环境工程学院,安徽合肥230009 [4]中山大学地球科学与工程学院,广东广州510275 [5]中国科学院深海科学与工程研究所,海南三亚572000

出　　处：《中国地质》2021年第1期229-246,共18页Geology in China

基　　金：国家自然科学基金青年基金项目(4160206);克什克腾旗金达矿业开发有限责任公司项目(20150008)联合资助。

摘　　要：内蒙古克什克腾旗长岭子斜长花岗斑岩位于大兴安岭锡林浩特增生杂岩带内。本文对长岭子斜长花岗斑岩进行了主微量元素地球化学以及锆石U−Pb年代学和Lu−Hf同位素研究。长岭子斜长花岗斑岩锆石206Pb/238U加权平均年龄为(248.1±4.7)Ma,是早三叠世岩浆活动的产物;继承锆石除外,样品中锆石具有正的εHf(t)值(5.78~12.41),二阶段模式年龄TDM2分别为914~488 Ma。长岭子斜长花岗斑岩具有较高的SiO2、Na2O和Al2O3含量以及较低的Fe2O3、MgO和CaO含量,属于偏铝质−过铝质的低钾−钙碱性系列I型花岗岩,富集Rb、K、U、Th、Pb、Sr等大离子亲石元素,亏损Nd、Ta、Ti等高场强元素。同时,斜长花岗斑岩具有高Sr低Y以及高Sr/Y比等特点,具有典型的埃达克质岩石特征,形成于加厚下地壳的部分熔融。综合上述地球化学特征,本文认为长岭子斜长花岗斑岩来源于加厚新生下地壳的部分熔融,表明早三叠世兴蒙地区并非岛弧的环境,而是处于碰撞造山环境,古亚洲洋在该时期已经闭合。The Changlingzi plagiogranite porphyry is located in the Xilinhot Late Paleozoic Accretion Complex within the Da Hinggan Mountains.This study is focused on the zircon U−Pb isotopic geochronology,Hf isotopic composition analysis and geochemistry of the Changlingzi plagiogranite porphyry.Zircon crystals from the plagiogranite porphyry yielded weighted average 206Pb/238U age of(248.1±4.7)Ma.The zircons from this porphyry have positiveεHf(t)values from 5.78 to 12.41,with TDM2(Hf)ages from 914 to 488Ma.The plagiogranite porphyry has high content of SiO2,Na2O and Al2O3,and low content of TiO2,MgO and CaO,showing a metaluminous–peraluminouslow-K to calc-alkaline affinity,with LREE enrichment and HREE depletion,suggesting I-type granite.In addition,the plagiogranite porphyry has high Sr and low Y values as well as high Sr/Y ratios(74.5~103.4),indicating that the plagiogranite porphyry belongs to adakite.It is suggested that the plagiogranite porphyry was formed by partial melting of the thickened newborn lower crust.And in Early Triassic,Xing’an–Mongolian orogenic belt was in a collisionorogeny tectonic setting,indicating that the Paleo-Asian Ocean had been closed in this period.

关 键 词：大兴安岭 早三叠世岩浆岩 锆石U−Pb定年 锆石HF同位素 地球化学 古亚洲洋 地质调查工程 

分 类 号：P597[天文地球—地球化学] P588.121[天文地球—地质学]