西秦岭造山带早中生代花岗岩成分多样性及形成机制  

Compositional Diversity of Early Mesozoic Granites in the West Qinling Orogen,China and Their Genetic Mechanism

作　　者：豆敬兆 何俊 黄曦光 陈福坤[2] DOU Jing-zhao;HE Jun;HUANG Xi-guang;CHEN Fu-kun(CAS Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,Anhui,China)

机构地区：[1]中国科学院广州地球化学研究所中国科学院矿物学与成矿学重点实验室,广东广州510640 [2]中国科学技术大学地球和空间科学学院,安徽合肥230026

出　　处：《地球科学与环境学报》2023年第2期227-239,共13页Journal of Earth Sciences and Environment

基　　金：中国博士后基金项目(2021M703224);国家自然科学基金项目(41872049)。

摘　　要：花岗质岩体产状及组成上的差异主要受控于源区性质和岩浆过程。以西秦岭造山带内几个代表性早中生代花岗岩为例,简要介绍其形成中所记录的岩浆过程,探讨花岗岩成分多样性的原因。西秦岭造山带内S型花岗岩是变泥质岩部分熔融的产物;根据地球化学特征可分为两类,即高Sr含量、低Rb/Sr值和稀土元素总含量的Group A,及低Sr含量、高Rb/Sr值和稀土元素总含量的Group B,其分别可由白云母水致熔融和脱水熔融形成。糜署岭岩体的暗色微粒包体中发育3类晶形和成分不同的锆石,其与寄主岩石的锆石具有一致的U-Pb年龄;其中,暗色微粒包体中的类型3锆石与寄主岩石中锆石具有一致的晶形和εHf(t)值,捕获于寄主岩石,而类型1和类型2锆石具有较高的Th/U值和εHf(t)值,结晶于混合程度不同的基性岩浆,其基性端元可能来自幔源岩浆;因此,糜署岭岩体的暗色微粒包体记录了壳-幔岩浆混合过程。中川岩体由形成时代没有明显差异的5个岩相呈同心环状产出;边部的似斑状花岗闪长岩被含斑中粒黑云母二长花岗岩侵入,中粒黑云母二长花岗岩被中粒电气石二云母花岗岩侵入,后者又被细粒黑云母二长花岗岩侵入;Rb-Sr-Ba微量元素特征显示各岩性之间不存在成分分异趋势;因此,中川岩体的环带结构是由多期次岩浆侵位、聚集形成的。The occurrence and compositional diversity of granitic pluton is determined by properties of source rocks and conditions of partial melting,and can be further modified by magmatic processes such as magma mixing,crystal fractionation and assimilation during the transfer.However,the role and relative importance of each process during pluton construction are still elusive.Several representative Early Mesozoic granitic plutons in the West Qinling orogen were chosen to illustrate how the magmatic processes control the compositional variation of granitic plutons.The S-type granites in the West Qinling orogen were derived from partial melting of metapelite and can be classified into two categories based on geochemical features,i.e.,high Sr content,and low Rb/Sr ratio and REE content(Group A),and low Sr content,and high Rb/Sr ratio and REE content(Group B).Groups A and B might have been produced through fluid-present and fluid-absent incongruent melting of muscovite,respectively,which can well explain respective contrasting major and trace elemental characteristics,and zircon and monazite saturation temperatures.Three types of zircon were identified in the microgranular mafic enclaves(MMEs)from Mishuling pluton based on the morphology.They have consistent zircon U-Pb age but different trace elemental and Hf isotopic compositions.Type-3 zircon develops{100}prisms and hasεHf(t)similar to these of zircon in the host granite.Hence type-3 zircon is interpreted as xenocryst captured from the host granitic magma.Type-1 and type-2 zircons are characterized by{100}+{110}and{110}prisms,respectively.They have relatively higher Th/U ratio andεHf(t)values than type-1 zircon,and may have crystallized from hybridized magmas with varying degrees of the mixing.The mafic endmember of the hybridized magma likely has mantle-derived affinity.Thus,the MMEs in Mishuling pluton record crust-mantle interaction.Zhongchuan pluton is comprised of five rock units from the periphery to the center,which mostly have indistinguishable zircon U-Pb ages

关 键 词：花岗岩 地球化学 早中生代 成分多样性 不一致熔融 岩浆混合 多期岩浆侵位 西秦岭 

分 类 号：P588.12[天文地球—岩石学] P581[天文地球—地质学]