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


Clinopyroxenes and Spinels in the System CaMgSi2O6-CaAl2SiO6-CaCrAlSiO6 : A Preliminary Report

Onuma, Kosuke;Tohara, Tatsuhide

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The system CaMgSi2O6-CaAl2SiO6-CaCrAlSiO6 has a wide liquidus field for spinel at 1 atm. In the CaMgSi2O6-rich portion, however, clinopyroxene appears as second phase and then spinel disappears to react with liquid and the phase assemblage at subsolidus temperatures becomes clinopyroxene single phase and clinopyroxene + spinel + anorthite, indicating in congruent melting of chromian pyroxene into spinel + liquid. Clinopyroxenes and spinels in the assemblage of clinopyroxene + spinel + liquid at 1 atm and higher pressure were analysed. The Cr2O3 contents of clinopyroxenes and spinels increase with increasing those of bulk compositions and attain 3.16 wt% and 48.99 wt% respectively, at the bulk composition containing 1.86 wt% Cr2O3. The Cr/Al ratios of spinels are higher than those of the bulk compositions and increase with an increase of Cr/AI ratios of the bulk compositions. Spinels and clinopyroxenes crystallizing from a composition containing 1.86 wt% Cr2O3 at 8 kbar and 1300℃ with over-saturated water contain about 70 wt% and 0.1 wt% Cr2O3, respectively. Spinels coexisting with clinopyroxene in the present system have higher Cr/Al ratios than the clinopyroxene.