摘要
花岗岩的源区、温压条件及与其他岩石的共生组合的研究可以限定其形成构造背景,了解其形成的深部动力学过程。本文对浙江中部中生代芙蓉山花岗斑岩及其暗色包体开展了全岩主微量元素、锆石U-Pb年代学和Hf同位素、Ti温度计和全岩Sr—Nd同位素研究,探讨芙蓉山花岗斑岩的成因类型、源区特征及其与镁铁质包体之间的关系,并进一步限定其构造背景。锆石U-Pb定年结果显示芙蓉山花岗斑岩加权平均年龄为133.6±1.6 Ma(MSWD=2.1,2σ),镁铁质包体加权平均年龄为130.3±4.2 Ma(MSWD=5.8,2σ),其成岩年龄基本一致,形成于早白垩世。全岩地球化学表明芙蓉山花岗斑岩属于亚碱性系列,同时具有低的Ga/Al(<2.6),高的Na_(2)O含量(2.75%~4.5%,平均3.78%),较高的全碱含量(Na_(2)O+K_(2)O=7.93%~8.75%),以及较低的锆石Ti饱和温度特征(631~690℃),这些特征显示芙蓉山花岗斑岩为I型花岗岩,而非A型花岗岩。芙蓉山花岗斑岩中锆石Hf同位素有比较大的范围[ε_(Hf)(t)=-10.9~-1.1],全岩[n(^(87)Sr)/n(^(86)Sr)]i=0.7062~0.7078,相对富集的ε_(Nd)(t)=-5.6~-4.7值;而包体表现为均一的[n(^(87)Sr)/n(^(86)Sr)]i=0.7071~0.7079和弱富集的ε_(Nd)(t)=-3.8~-2.8特征。野外及岩相学和元素地球化学特征显示典型的岩浆混合特征。镁铁质包体源区可能来自于俯冲交代地幔,芙蓉山花岗斑岩则形成于古老富钾地壳熔体和交代地幔熔体混合后的结晶分异。混合模型计算表明混合比例为:~80%的地幔端元和~20%地壳端元。浙江中部芙蓉山富钾I型花岗斑岩与镁铁质包体共生可能指示其形成于古太平洋板块俯冲后撤初始弱伸展拉张的构造背景。
Objectives:By comparing the geochemistry and isotopic compositions of Furongshan granitic porphyry and mafic microgranular enclaves from central Zhejiang province,the genesis of Furongshan granitic porphyry,the characteristic of source area and the relationship between granitic porphyry and mafic microgranular enclaves are able to be explored,through which further constraints of the tectonic setting,and the geodynamic process of the Late Mesozoic crust—mantle magma interaction in the South China Plate could be revealed.Methods:Based on the field work,through the microscope observation,the whole rock chemical analysis,LA ICP-MS zircon U-Pb dating,Ti-thermometer,Sr—Nd isotopic compositions and Hf isotopes of Mesozoic host granitic porphyry and their mafic microgranular enclaves(MMEs)from Furongshan pluton.Results:Zircon U-Pb dating results show that the weighted mean n(^(206)Pb)/n(^(238)U)age of Furongshan granitic porphyry is 133.6±1.6 Ma(MSWD=2.1,2σ),and the weighted mean n(^(206)Pb)/n(^(238)U)age of mafic microgranular enclaves is 130.3±4.2 Ma(MSWD=5.8,2σ).Their diagenetic ages are basically the same and formed in the early Cretaceous.The Furongshan granitic porphyry are sub-alkaline with low Ga/Al(<2.6)(10000·Ga/Al=2.19~2.48)and high Na_(2)O(2.75%~4.5%),enriched in alkalis(Na_(2)O+K_(2)O=7.93%~8.75%).And calculated results based on zircon Ti-thermometry indicate a relatively low magmatic temperature(631~690℃).The Furongshan granitic porphyry has a large range of zircon ε_(Hf)(t)values(-10.9~-1.1)and exhibits initial[n(^(87)Sr)/n(^(86)Sr)]i ratios of 0.7062 to 0.7078 andε_(Nd)(t)values of-5.6 to-4.7,the enclaves have relatively uniform initial[n(^(87)Sr)/n(^(86)Sr)]i ratios of 0.7071 to 0.7079 andε_(Nd)(t)values of-3.8 to-2.8.Conclusions:These petrographical and geochemical characteristics of the Furongshan granitic porphyry suggest I-type granitic affinities rather than A-type granitic affinities.Field and petrography and geochemistry characteristics suggesting Furongshan mafic microgranular encla
作者
杜秀玲
汪方跃
闫海洋
顾海欧
孙贺
葛粲
DU Xiuling;WANG Fangyue;YAN Haiyang;GU Haiou;SUN He;GE Can(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei,230009;Ore Deposit and Exploration Center(ODEC),Hefei University of Technology,Hefei,230009;Chinese Academy of Sciences(CAS)Key Laboratory of Crust—Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei,230026)
出处
《地质论评》
CAS
CSCD
北大核心
2022年第1期18-46,共29页
Geological Review
基金
国家重点研发计划“深地资源勘查开采”重点专项(编号:2016YFC0600404)
国家自然科学基金资助项目(编号:41873034)的成果。
关键词
赣杭构造带
芙蓉山岩体
Ⅰ型花岗岩
岩浆混合
古太平洋俯冲
洋壳俯冲后撤
Furongshan,Gan-hang Tectonic Belt
Ⅰ-type granites
magma mixing
Paleo-Pacific plate subduction
oceanic crust subduction and retreat
