花岗岩中原生与次生白云母的鉴别特征及其地质意义--以赣南富城强过铝质花岗岩体为例  

Petrological discrimination between primary and secondary muscovites and its geological implications:A case study of Fucheng peraluminous granite pluton in southern Jiangxi

作　　者：章邦桐[1] 吴俊奇[1] 凌洪飞[1] 陈培荣[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,江苏南京210093

出　　处：《岩石矿物学杂志》2010年第3期225-234,共10页Acta Petrologica et Mineralogica

基　　金：中国核工业地质局十一五基础科研项目(YK08);内生金属矿床成矿机制研究国家重点实验室研究项目(2008CI-04);教育部科学研究重大资助项目(306007)

摘　　要：通过显微镜下观察和电子探针成分分析,发现赣南富城强过铝质花岗岩中存在3种类型白云母,即原生白云母、交代型白云母和次生白云母,其平均晶体化学式分别为:K1.62Na0.06Fe0.32Mg0.39Ti0.02Al4.89Si6.54O10(OH)4(原生白云母)、K1.55Na0.07Fe0.43Mg0.24Ti0.03Al4.96Si6.50O10(OH)4(交代型白云母)、K1.51Na0.07Fe0.27Mg0.21Ti0.00Al4.98Si6.65O10(OH)4(次生白云母)。根据富城花岗岩主要造岩矿物的结晶顺序(斜长石→钾长石→黑云母→白云母→石英),结合白云母、黑云母稳定曲线及合成花岗岩初融曲线对比分析,富城强过铝质花岗岩中交代型白云母是在花岗岩结晶过程中交代较早晶出的黑云母形成的,其形成温度高于花岗岩熔体的固相线温度(～650℃),故应归属于原生白云母。本文提出根据岩石学宏观特征、岩石化学特征及岩相学微观特征区分花岗岩中原生白云母与次生白云母的综合鉴别方法。The Fucheng composite pluton is exposed in an area of about 850 km2 and intruded into Sinian-Cambrian strata with a distinctive thermometamorphic aureole of hornstone.The first stage major phase granite is coarse-medium-grained porphyritic biotite granite,whose major minerals are quartz,K-feldspars,plagioclase and lesser biotite and muscovite,and whose accessory minerals are zircon,apatite,topaz,tourmaline etc.The second stage additional phase granite is medium-fine-grained two-mica granite in the form of a small stock,whose major rock-forming minerals are quartz,K-feldspars,plagioclase,muscovite and biotite.As for petrochemistry,the indices of alumina saturation [ACNK=Al2O3/（CaO＋Na2O＋K2O）] of Fucheng pluton are higher than 1.0 （ACNK=1.22 on average）,indicating that the Fucheng pluton belongs to strongly peraluminous granite.The whole rock Rb-Sr isochron ages of the first main-stage granite are 226～203 Ma,whereas the zircon U-Pb ages are 231～239 Ma,implying that the granite is an intrusive product of late Indosinian magmatic cycle.Based on microscopic observation and electron microprobe analyses,the authors recognized three kinds of muscovites,namely primary,metasomatic and secondary muscovites,in the Fucheng strongly peraluminous granite pluton,and their average crystallochemical formulas are respectively as follows：K1.62Na0.06Fe0.32Mg0.39Ti0.02Al4.89Si6.54O10（OH）4 （primary muscovite）,K1.55Na0.07Fe0.43Mg0.24Ti0.03Al4.96Si6.50O10（OH）4 （metasomatic muscovite）,K1.51Na0.07Fe0.27Mg0.21Ti0.00Al4.98Si6.65O10（OH）4 （secondary muscovite）.According to the crystallizing sequence of main rock-forming minerals （plagioclase→K-feldspar→biotite→muscovite→quartz） in combination with an analysis of muscovite and biotite stability curves and syntectic granite solidus,it is considered that the metasomatic muscovite was formed by the replacement of early crystallized biotite in the crystallization process of the granite melt.Moreover,as uhe crystallization temperature of the musco

关 键 词：原生白云母 次生白云母 强过铝质花岗岩 富城岩体 

分 类 号：P588.121[天文地球—岩石学] P578.959[天文地球—地质学]