骑田岭花岗岩体的岩浆混合成因:寄主岩及其暗色闪长质包体的锆石U-Pb年龄和Hf同位素证据  

Qitianling Granite Magma Mixing Origin:The Host Rock and Its Microgranular Dioritic Enclaves of Zircon U-Pb Dating and Hf Isotope Evidence

作　　者：刘勇[1] 李廷栋[1,2] 肖庆辉[1] 耿树方[1] 王晓霞[1] 陈必河 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院,北京100037 [3]湖南省地质调查研究院,湖南湘潭411100

出　　处：《地质科技情报》2011年第2期19-27,共9页Geological Science and Technology Information

基　　金：中国地质大调查项目(1212010611803);中国地质调查局基础地质综合研究项目(1212010811064)

摘　　要：燕山期骑田岭花岗岩体的仰天湖单元中花岗岩以发育暗色闪长质微细粒包体为特征。这些包体大小不等,呈被打散的片云状或次圆状,颜色较寄主岩深,粒度较细。在锆石内部结构的CL图像特征研究基础上,用LA-ICP-MS和MC-ICP-MS测定了锆石U-Pb年龄及Hf同位素组成,探讨了寄主二长花岗岩、暗色闪长质微细粒包体的锆石U-Pb年代学及Hf同位素组成特征。结果表明,寄主二长花岗岩的结晶年龄为(167.5±1.7)Ma和(155.4±4.3)Ma;闪长质微细粒包体的结晶年龄为(181.7±3.4)Ma和(167.6±3.9)Ma,寄主岩和包体均存在两组锆石年龄;对应的ε(Hf)t值为-13.2^-1.9与-8.3^+6.7,说明该岩体非单一源区岩浆物质形成,至少是两个源区岩浆混合作用的结果。结合寄主岩、包体的年龄以及Hf同位素组成特征,认为骑田岭花岗岩是以古老地壳物质熔融为主体的壳源岩浆与地幔的幔源岩浆高度混合的产物。壳、幔岩浆混合作用可能在18 2Ma前形成以壳源岩浆为主的岩浆房,在168 Ma时深部幔源基性岩浆进入壳源酸性岩浆房发生岩浆混合,壳、幔岩浆混合一直持续到15 5Ma左右。A large number of directional microgranular dioritic enclaves are found in Yangtianhu from Qitianling composite body.Based on the analysis for the inner structural CL images of zircons,the U-Pb ages and Hf isotopes of zircons from the host adamellite and mafic microgranular enclaves have been discussed using in situ zircon analysis of the LA-ICP-MS and MC-ICP-MS.The ages of（155.4±4.3） Ma and（167.5±1.7） Ma from host adamellite,（167.6±3.9） Ma and（181.7±3.4） Ma from enclaves have been obtained,respectively.Both of them have two groups of zircon ages,their εHf（t） ranging from slight positive to negative values.This suggests they were not formed by the magmas derived from one single source,but from at least two sources.The Yangtianhu adamellite intrusion was formed by the mingling between the partial melting products from crustal materials and magma derived from mantle.The crust-mantle mixing could be marked before 182 Ma.The mixture between crust-and mantle-derived magmas widely started in chamber due to the injecting of basic magma at 168 Ma,and ended around in 155 Ma.

关 键 词：暗色闪长质微细粒包体 锆石U-Pb定年 HF同位素 壳、幔岩浆混合 

分 类 号：P581[天文地球—岩石学]