The phase relations and the chemical variations of Ca-amphibole, MgFe-amphibole and Na-amphibole under low water vapor pressure.

本文在675-850 ℃的熔融温度范围内，在1和2kbar的水压和FMQ缓冲液的氧逸度下，研究了斜长岩（<50>Mg_2）-阳起石（Mg<50>_2）-斜长石（An_0，An_<20>2，An_3<40>）-石英-水体系的相关系。实验在标准冷封压力容器（Koatsu-Kagaku MR 01 -10）中进行，在钙镁闪石-阳起石-斜长石（An_0）-石英体系中，钙镁闪石（Cum）与钙角闪石以液相和气相共存。钙闪石与钙镁闪石之间存在较宽的混溶性间隙。在725 ° C时，存在具有高达4.1wt% CaO的本体系统组合物，并且随着本体Ca含量的增加，在cummingtonite中的Ca含量系统地增加。钙铝榴石稳定场向富含阳起石端员方向移动。在角闪石-阳起石-斜长石（An_<20>或An_<40>）-石英体系中，角闪石（Cum）常与阳起石或阳起石角闪石伴生。相关系与含An_0的体系相似，但钙角闪石的稳定性随着钙斜长石组分的增加而逐渐增加，从而使各自的稳定场向富钙铝榴石端员方向移动。在这些体系（An_<20>或An_<40>）中，在1 kbar和5 kbar下的稳定场相似。与在5 kbar下合成的cummingtonite相比，在1 kbar下合成的cummingtonite具有较低的蓝闪石含量。三个体系中角闪石的化学组成反映了它们相对于变质条件的高平衡温度，单相角闪石位于公认的“混溶间隙”内，或共存的组合物显示出广泛的相互固溶体。

Phase relations in the systems cummingtonite(Mg_<50>)-actinolite(Mg_<50>)- plagioclase (An_0,An_<20>,An_<40>)-quartz-water have been studied within the melting range 675-850ﾟC under water pressures of 1 and 2 kbar and oxygen fugacities of the FMQ buffer. The experiments were performed in standard 'cold seal' pressure vessels (Koatsu-Kagaku MR01-10).In the system cummingtonite-actinolite-plagioclase(An_0)-quartz, cummingtonite (Cum) coexists with Ca-amphibole, liquid and vapor. Cummingtonite is separated from Ca-amphibole by a wide miscability gap. At 725ﾟC cummingtonite is present is present for bulk system compositions with up to 4.1 wt % CaO, and Ca-content in cummingtonite increases systematically with increasing bulk Ca content. The cummingtonite stability field is shifted toward the actinolite-rich end member. As compared to Ca-amphibole and cummingtonite synthesized at 5 kbar, they have the lower Na content at 1 kbar.In the system cummingtonite-actinolite-plagioclase(An_<20> or An_<40>)-quartz, cummingtonite (Cum) is always accompanied by actinolite or actinolitic hornblende. The phase relations are otherwise similar to those in the system with An_0 but Ca-amphiboles stability progressively increases with more calcic plagioclase component, so that the respective stability fields are shifted toward the cummingtonite-rich end member. In these systems(An_<20> or An_<40>) the stability field of cummingtonite at 1 kbar is similar to that at 5 kbar. As compared to cummingtonite synthesized at 5 kbar, it has the lower glaucophane content at 1 kbar.Chemical compositions of amphiboles in the three systems reflect their high temperature of equilibration relative to metamorphic conditions, with either single-phase amphiboles lying within accepted "miscability gaps" or coexisting compositions showing extensive mutual solid solution.