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本文系统地讨论了西藏过铝花岗岩中斜长石、钾长石、黑云母、白云母和电气石的矿物化学特征。结果表明:岩石中的斜长石均以Ab为主,占78.73%~100%,An分子为0.13%~18.93%,而Or分子仅为0.19%~3.74%;在长石的成分分类图解中多分布于更长石区内,少量分布于钠长石区。钾长石的端元组分中Or含量最高,为81%~98.48%,Ab为1.52%~19.00%,基本不含An分子,在成分分类图解中集中分布在Ab—Or线的正长石区内。斜长石中Ab>An>Or,主要属更长石,极少量为中长石;钾长石具有高Or含量,显示Or>>Ab>>An,属钾透长石。白云母在以22个氧原子计算的分子式中,Si与Al的阳离子数均较高,其中Si为6.0575~6.6412,属多硅白云母;黑云母中Si阳离子数绝大多数小于6,值介于5.3227~6.1265之间,平均为5.5718;Al离子数为1.8735~2.6464,四面体配位为Si、AlⅣ所占据,八面体配位的阳离子中AlⅥ为0.2101~1.7388,大离子位中以K为主。过铝花岗岩中黑云母的Mg/(Mg+Fe)比全岩的Mg/(Mg+Fe)比值略高,但二者具有正相关关系,说明了其成因仍以岩浆成因为主。在云母类矿物的成因图解显示,研究区内大多数黑云母均位于C区,属壳源。
This paper systematically discusses the mineralogical and chemical characteristics of plagioclase, potassium feldspar, biotite, muscovite and tourmaline from the peraluminous granites in Tibet. The results show that all the plagioclase in the rock are mainly Ab, accounting for 78.73% -100%, An molecule is 0.13% -18.93%, while Or molecule is only 0.19% -3.74%. In the compositional classification of feldspar More distributed in the longer stone area, a small amount of distribution in the albite area. The content of Or is the highest in the terminal element of K-feldspar, ranging from 81% to 98.48% for Ab and from 1.52% to 19.00% for Ab, which is almost free of An molecules. Area. In the plagioclase, Ab> An> Or is mainly a feldspar, with a very small amount of feldspar. K-feldspar has a high content of Or, which shows that Or >> Ab >> An is a potassium-feldspar. Muscovite in 22 oxygen atoms in the formula, the number of Si and Al cations are high, of which Si is 6.0575 ~ 6.6412, is a multi-silica muscovite; biotite most of the number of Si cations less than 6, the value of mediated Between 5.3227 and 6.1265, with an average of 5.5718; the number of Al ions is 1.8735 ~ 2.6464, the tetrahedral coordination is Si and the AlIV is occupied, the AlVI in the octahedral coordination cation is 0.2101 ~ 1.7388, the Lord. The ratio of Mg / (Mg + Fe) to biotite in perovskite is slightly higher than the ratio of Mg / (Mg + Fe) in whole rock, but there is a positive correlation between them. The genesis of the mica minerals shows that most of the biotite in the study area is located in the C zone, which is a source of crusts.