1989 Fiscal Year Final Research Report Summary
The phase relations and the chemical variations of Ca-amphibole, MgFe-amphibole and Na-amphibole under low water vapor pressure.
| Project/Area Number |
63540646
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Joetsu University of Education |
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Principal Investigator |
OBA Takanobu Joetsu Univ. Education, Assistant, 学校教育学部, 助手 (30194278)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Ca-amphibole / Mg-Fe amphibole / Cummingtonite / Na-amphibole / low water vapor pressure |
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| Research Abstract |
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.
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