赣杭构造带灵山花岗岩体黑云母的矿物化学特征及其对岩石成因的指示意义  

Mineral chemistry of biotite and its petrogenesis implication in Lingshan granite pluton,Gan-Hang Belt,SE China

作　　者：叶茂[1] 赵赫[2] 赵沔 舒珣 张若曦[1] 杨水源[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 [2]成都理工大学地球科学学院,成都610059

出　　处：《岩石学报》2017年第3期896-906,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41403022);中央高校基本科研业务费专项资金资助项目(CUGL150401)联合资助

摘　　要：灵山花岗岩体在平面上为一环状分布的侵入体,中心为角闪石黑云母花岗岩,外围为黑云母花岗岩。在角闪石黑云母花岗岩中分布有大量的暗色镁铁质微粒包体。黑云母是大多数中酸性火成岩中比较重要的一种镁铁质矿物,它能很好地反映寄主岩浆的属性和成岩时的物理、化学条件,因此,本文对这两种花岗岩及镁铁质微粒包体中的黑云母开展了系统的岩相学观察和电子探针化学组成研究,探讨灵山岩体的物质来源、成岩条件和岩浆的混合作用过程。研究结果表明两种花岗岩体的黑云母具有不同化学成分,而暗色镁铁质微粒包体中黑云母的化学成分则变化较大。三种黑云母均在低氧逸度条件下晶出。两种花岗岩中的黑云母均富Fe贫Mg,属于铁质黑云母,含铁系数[(Fe^(3+)+Fe^(2+))/(Fe^(3+)+Fe^(2+)+Mg^(2+))]分别为0.65~0.70,0.72~0.78,FeOT/MgO均接近7.04。MF值[2×Mg/(Fe^(2+)+Mg+Mn)]分别为0.64~0.76和0.48~0.60,指示两种花岗岩的物质来源都是以壳源为主。镁铁质微粒包体中黑云母的MF值变化范围比较大,为0.63~1.06,为铁质黑云母到镁质黑云母,暗示包体岩浆经历过不同程度的岩浆混合作用。镁铁质微粒包体中部分黑云母与角闪石黑云母花岗岩中黑云母的结晶条件相似,而部分则有明显差异,推测是由于基性的镁铁质包体岩浆注入到酸性的花岗岩浆是一个连续多阶段的过程。The Lingshan composite granite pluton is composed of an outer zone of biotite granite,and a central part of amphibolebiotite granite which contains many mafic microgranular enclaves（ MME）. Biotite is an important ferromagnesian mineral in most of intermediate-felsic igneous rocks, and its mineral chemistry data can record the properties of magma and the petrogenetic physicochemical conditions. In this study,we carried out a detailed petrographic study together with electric micro-probe analysis on biotites for the biotite granite,the amphibole-biotite granite and the MME,to discuss the source,physicochemical conditions,and the magma mingling/mixing processes in the Lingshan composite granite pluton. The results show significantly different chemical compositions for biotites from the biotite granite and the amphibole-biotite granite,while chemical compositions of biotites in the MME are variable. The crystallization of these biotites was all in a low oxygen fugacity. The biotites in amphibole-biotite granite and biotite granite are both rich in Fe,poor in Mg,and belong to ferri-biotite. The ratio of（ Fe^3＋＋ Fe^2＋）/（Fe^3＋＋ Fe^2＋＋ Mg^2＋） are 0. 65 -0. 70 and 0. 72 - 0. 78,respectively. The ratios of FeOT/MgO of biotites in both granites are close to 7. 04. The MF values [2 × Mg/（Fe^2＋＋ Mg ＋ Mn）] are 0. 64 to 0. 76 for biotite from the amphibole-biotite granite,0. 48 to 0. 60 for the biotite from the biotite granite,suggesting these tow granites are both derived from crustal source rocks. The biotites in MME vary from ferri-biotite to magnesio-biotite,and their MF values range between 0. 63 and 1. 06,which imply that magma of MME experienced magma mixing/mingling in various degrees. Amphibole-biotite granite and parts of MME have a similar crystallization condition,while other MME are obviously different with amphibole-biotite granite. The contrast between amphibole-biotite granite and MME may be a consequence of continuous and multistage interaction between felsic and mafic mag

关 键 词：黑云母 矿物化学 结晶条件 岩浆混合作用 灵山花岗岩 

分 类 号：P578.959[天文地球—矿物学]