华北陆块东南缘蚌埠地区侏罗纪花岗岩中多种类型白云母的识别及其地质意义  

Identification and Geological Significance of Various Types of Muscovite in Jurassic Granite of Bengbu Area on the Southeast Margin of North China Craton

作　　者：吴天昊 徐丽娟 肖益林[3,4] 刘盛遨 WU Tianhao;XU Lijuan;XIAO Yilin;LIU Sheng'ao(Institute of Earth Sciences,China University of Geosciences,Beijing 100083,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing100083,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei,Anhui 230026,China;CAS Key Laboratory of CrustMantle Materials and Environments,University of Science and Technology of China,Hefei,Anhui 230026,China)

机构地区：[1]中国地质大学(北京)科学研究院,北京100083 [2]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083 [3]中国科学技术大学地球和空间科学学院,安徽合肥230026 [4]中国科学技术大学中国科学院壳幔物质与环境重点实验室,安徽合肥230026

出　　处：《现代地质》2020年第3期532-544,共13页Geoscience

摘　　要：三叠纪华南俯冲陆壳已经延伸到华北克拉通东南缘的蚌埠地区,而该地区的俯冲陆壳是否经历超高压变质仍存在诸多争议。对华北克拉通东南缘蚌埠地区的侏罗纪花岗岩--荆山岩体中的暗色残留体、主体花岗岩以及细晶岩脉中的白云母进行岩相学观察、电子探针和拉曼光谱分析,结果表明荆山残留体和主体花岗岩中白云母颗粒较大且相对于一般花岗岩中原生的、次生的白云母具有较高的Si、Fe+Mg原子数和较低的Al原子数。拉曼光谱分析结果显示残留体和主体花岗岩中大颗粒白云母也具有相似的铝原子桥氧键(Al,O(br))的拉曼位移(421 cm-1),低于经历超高压的黄镇榴辉岩中多硅白云母的原子数和铝原子桥氧键的拉曼位移,而高于本研究中未经历超高压变质作用的奥地利Spail片岩中的白云母。残留体和花岗岩中大颗粒白云母的主量元素和拉曼位移特征指示其为变质成因的多硅白云母。因此,可以利用多硅白云母地质压力计来指示花岗岩形成的压力,并且确定荆山花岗岩发生部分熔融的压力为1.0~1.3 GPa。荆山花岗岩的源岩为华南深俯冲的陆壳碎片,华南板块俯冲到华北克拉通东南缘的深度为33~45 km,相当于华北克拉通中下地壳深度。The Triassic subduction of South China continental crust is generally considered to have extended to the Bengbu region(SE margin of the North China craton),yet whether the subduction there had caused ultra-high-pressure(UHP)metamorphism remains controversial.Primary phengite can be used as a geobarometer to estimate the pressure of rock formation.Petrographic observation,electron probe microanalysis(EPMA)and Raman spectral analysis have been performed on the muscovite in the restite,its granite host and the aplite vein from the Jurassic Jingshan granites in the SE margin of the North China Craton.The muscovite in the restite and granite host are coarser,and have higher Si and(Fe+Mg),but lower Al atomic contents than the muscovite in common granites.The muscovite in the restite and granite host also show similar Raman shift(421 cm-1)and aluminium atom bridge-bond(Al,O(br)),which are lower and higher than that of the white micas,respectively,in the UHP eclogite and non-UHP schist of this study.Therefore,major element contents and Raman shifts of the muscovite suggest that coarse-grained muscovite in the residual and granite are primary metamorphic phengite.Applying geobarometry,the melting pressure of the Jingshan granite is estimated to be 1.0 to 1.3 GPa.The source of the Jingshan granite may have been the subducted South China continental crust.The subducting depth of the South China plate beneath the NE margin of the North China Craton was at least 33 to 45 km,equivalent to the middle and lower crust there.

关 键 词：白云母 多硅白云母 残留体 俯冲陆壳 华北克拉通 

分 类 号：P534.5[天文地球—古生物学与地层学]