4. System CaO–MgO–SiO₂

The main focus in this chapter is on the enstatite-diopside join, which includes petrologically most important compositions in the CMS system, and is, undoubtedly, the most thoroughly investigated binary join in the experimental petrology. The earlier investigations concentrated mainly on the subsolidus phase relations since the data of Davis and Boyd [155] suggested that the compositions of the coexisting orthopyroxene and clinopyroxene are primarily temperature dependent and thus suitable as a geothermometer. The first experimental data at 1 atm were reported by Atlas [91], Boyd and Shairer [118], Kushiro [287], Yang and Foster [469], and Yang [468]. Later studies at 1 atm were conducted to elucidate the stability of the second field of orthopyroxene found at high temperatures [99, 172, 253, 305]. First subsolidus data at high pressures were reported by Warner and Luth [439], Mori and Green [329], and Lindsley and Dixon [296]. A good summary of these studies was given by Carlson [132] and Carlson and Lindsley [134].