花岗岩—H2O—HF体系相关系及氟对花岗质熔体结构的影响

通过在0.1GPa压力下钠长花岗岩-H₂O-HF体系相关系实验获得,随体系F含量的增加,石英的温度稳定域上限升高,长石的温度稳定域上限降低;石英、碱性长石的晶-液平衡热力学计算表明,F导致花岗质熔体中组分SiO₂的活度增加,组分NaAlSi₃O₈和KAlSi₃O₈的活度减小,且NaAlSi₃O₈活度较KAlSi₃O₈活度减小幅度大。这些结果显示了F在花岗质熔体中与Si以外的阳离子Al、Na、K等产生了结合,且F与Na结合的优先性大于K,破坏了具有电荷平衡离子Na、K的AlO₂^-四面体,使熔体架状网格中Si/(Si+Al)和K/Na比值增大。通过F与H₂O对花岗岩体系相平衡的影响比较,作者认为F不与Si结合是它与OH^-在干扰熔体结构方面的最大区别。

PHASE RELATIONSHIP IN THE GRANITE-H2O-HF SYSTEM AND THE EFFECT OF F ON GRANITIC MELT STRUCTURE

Experiments carried out on the system granite-H₂O-HF at 0.1G Pa show that the upper temperature limite raises for thestability field of quartz and falls for the stability fieldof alkali-feldspar as F contents increase. The calculated results of quartz, alkali-feldspar crystal-liquid equilibriumshow that the activity of SiO₂ in melt increases and the activities of NaAlSi₃O₈ (Ab)and KAlSi₃O₈ (Or) decrease, with a greater decreasing extent for α_Ab^L than α_Or^L. These systematic changes are believed to be caused by F complexing with A1, Na, K, but not Si in melt, and are consistent with F decomposing AlO₂^- tetrahedra and preferentially forming coplexes with Al, Na rather than K. The comparison between effects of F with that of H₂O on phase equilibrium suggests that the maximum differenceaffectingmelt structure between F and OH is F complexing without Si and OH complexing with Si in granitic melt.