Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XVIII, No.3


Study of the System CaMgSi2O6-CaFe^[3+]AlSiO6-CaAl2SiO6-CaTiAl2O6 : III. The Join CaMgSi2O6-CaFe^[3+]AlSiO6-CaTiAl2O6 at 1 atm

Akasaka, Masahide;Onuma, Kosuke

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The join CaMgSi2O6-CaFe^[3+]AlSiO6-CaTiAl2O6 was studied in air at 1 atm by the ordinary quenching method. Clinopyroxene(ss), forsterite, perovskite, magnetite(ss), spinel(ss), anorthite, melilite, unknown phase X and hibonite were encountered. Phase X was analysed by EPMA. At liquidus temperatures the following assemblages are confirmed: clinopyroxene(ss) + forsterite + spinel(ss) + liquid, clinopyroxene(ss) + magnetite(ss) + spinel(ss) + liquid, forsterite + perovskite + spinel(ss) + liquid, and magnetite(ss) + spinel(ss) + phase X + liquid. At subsolidus temperatures clinopyroxene(ss) single phase field extends up to 18 wt.% CaTiAl2O6, showing that the content of TiO2 in clinopyroxene(ss) increases with increasing CaFe3+ AlSiO6. Following phase assemblages were confirmed in the subsolidus regions: clinopyroxene(ss) + perovskite, clinopyroxene(ss) + perovskite + spinel(ss), clinopyroxene(ss) + perovskite + melilite (+ anorthite), clinopyroxene(ss) + perovskite + spinel(ss) + melilite + anorthite, clinopyroxene(ss) + perovskite + anorthite + spinel(ss), and clinopyroxene(ss) + perovskite + hibonite + anorthite. Even in the field of clinopyroxene(ss) + perovskite, TiO2 content in clinopyroxene(ss) continues to increase and attains up to 9.20% TiO2 and 18.57% Al2O3. An implication of the join to Ti-rich fassaitic pyroxene from the alkalic rocks is discussed.