The diopside-kyanite join at high pressures and temperatures

Abstract

Initial mixes of composition (molecular proportions) 2 anorthite: 2 enstatite: diopside have been crystallized at 1200°C over a pressure range of 13.5–36 kb. The stable mineral assemblage changes from anorthite+clinopyroxene solid solution+orthopyroxene at 13.5 kb to clinopyroxene solid solution+garnet+minor quartz at 18 kb to clinopyroxene solid solution+garnet+minor quartz+minor kyanite at 22.5–36 kb. The proportion of garnet and its grossular content increases with increasing pressure. On addition of 1/2, 1 and 2 moles of jadeite to the initial mix, crystallization of garnet is markedly inhibited and the grossular content decreases. This study has application to the relative stability of clinopyroxene-kyanite or garnet-quartz assemblages in natural rocks such as eclogites and grospydites from kimberlite pipes.