大兴安岭中南段哈力黑坝岩体岩浆混合作用:暗色包体岩相学、年代学和锆石Hf同位素启示  

Magmatic migmatization of Haliheiba pluton:Petrographic study of dark inclusion,U-Pb chronology and Hf isotope of zircon mineral in central and southern section of the Da Hinggan Mountains area

作　　者：魏巍 陈建平[1] 黄行凯[2] 祝新友[2] 徐巧 刘孜[2] 

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]北京矿产地质研究院,北京100012

出　　处：《矿产勘查》2017年第6期948-956,共9页Mineral Exploration

基　　金：中国地质调查局国家二级项目内蒙古赤峰有色金属基地综合地质调查(编号:DD20160072)资助

摘　　要：哈力黑坝岩体作为大兴安岭中南段地区重要的花岗岩体之一,以发育大量暗色包体为特征。文章对寄主岩中细粒黑云母花岗岩中的暗色包体展开了岩相学、锆石U-Pb年代学和Hf同位素分析研究,旨在探讨哈力黑坝岩体的岩浆混合作用。岩相学研究表明,暗色包体常呈椭球状,与寄主岩石的接触关系是截然的,可见大量自寄主岩浆捕获的钾长石巨晶,包体中发育有寄主岩石的反向脉,石英眼斑、镁铁质团块和针状磷灰石等,反映出暗色包体具有显著的岩浆混合作用特征。锆石U-Pb年代学表明,暗色包体的年龄为(136.9±1.1)Ma,与寄主岩年龄在误差范围内一致,进一步证实了岩浆混合成因。锆石Hf同位素显示,暗色包体具有正ε_(Hf)(t)值(+4.4^+9.0)和年轻的二阶段Hf模式年龄(519~759 Ma),与寄主岩具有相似的Hf同位素特征,表明二者具有相似的源区性质。寄主岩主要来自起源于亏损地幔年轻地壳物质的部分熔融;暗色包体为同源岩浆偏基性端元与酸性岩浆混合的产物,其原始岩浆应该更偏基性,可能来自起源于亏损地幔的玄武质岩浆。结合前人的研究成果,哈力黑坝岩体的岩浆混合作用可能受板内伸展环境下底侵作用的制约。As one of the important granite plutons in central and southern of the Da Hinggan Mountains area, Haliheiba pluton is characterized with the widespread dark inclusions. The detailed study for the dark inclusion in middle-fine grained biotite granite were conducted in aspects of petrography, zircon U-Pb chronology and Hf isotope in order to reveal the magmatic migmatization of Haliheiba pluton. The petrographic study results show that the black inclusions are almost axiolitic, there is a sharp contact relationship with the host rock. The giant K-feldspar crystal, back veins of the host rock, quartz eyespots, mafic agglomerates and acicular apatites indicate the remarkable magmatie process. The chronological study result of zircon U-Pb shows that the age of the black inclusion is （ 136.9＋- 1.1） Ma, which is consistent with the host rock in range of error, providing the further evidence of magma mixing. The black inclu- sions have high positive εHf（t） values （ ＋4.4- ＋9.0） and young Hf model ages （ 519-759 Ma）, showing the similarity to the host rock in zircon Hf isotopic composition. The host rock is derived from the partial melting of the nascent crustal materials originated from the depleted mantle, while the black inclusions are the product of the mixing of acidic magmas and marie magmas, whose primitive magma should be more mafic, probably derived from the depleted mantle. Combined with the previous research results, the mixing magmatism in Haliheiba is probably constrained by the underplating in intraplate extension environment.

关 键 词：暗色包体 岩浆混合作用 哈力黑坝 大兴安岭中南段 

分 类 号：P588.12[天文地球—岩石学] P597.3[天文地球—地质学]