CaMgSi₂O₆-CaFeAlSiO₆-CaTiAl₂O₆系におけるTiに富むファッサイト質輝石(<特集>造岩鉱物研究の現状と展望-地団研第33回総会鉱物学ミニシンポジウム-)

抄録

Phase equilibria in the join CaMgSi₂O₆-CaFe³⁺AlSiO₆-CaTiAl₂O₆ have been determined in air at 1 atm by the ordinary quenching method. At subsolidus temperatures the single phase field of clinopyroxene extends up to 19 wt. %. Even in the field of clinopyroxene + perovskite, the TiO₂ content in clinopyroxene continues to increase and attains 9.2 wt. % TiO₂ with 24.8 wt. % Al₂O₃. An interesting fact is that unusual clinopyroxenes which contain more A1IV than Silv are present in the CaFeAlSi0₆-rich region. At subliquidus temperatures the liquid is richer in Ti, Al, and Fe³⁺ than the coexisting pyroxene. The clinopyroxenes coexisting with liquid contain less TiO₂, A1₂0₃ and Fe₂0₃ than those crystallized at subsolidus temperatures. The system CaMgSi₂O₆-CaFe³⁺AlSiO₆-CaTiAl₂0₆ is relevant in evaluating the crystallization trend of clinopyroxenes in udersaturated alkalic rocks.