Experimental Investigation and Optimization of Thermodynamic Properties and Phase Diagrams in the Systems CaO-SiO2, MgO-SiO2, CaMgSi2O6-SiO2 and CaMgSi2O6-Mg2SiO4 to 1{middle dot}0 GPa

Using experimental results at 1·0 GPa for the systemsCaO–SiO₂, MgO–SiO₂, CaMgSi₂O₆–SiO₂ and CaMgSi₂O₆–Mg₂SiO₄,and all the currently available phase equilibria and thermodynamicdata at 1 bar, we have optimized the thermodynamic propertiesof the liquid phase at 1·0 GPa. The new optimized thermodynamicparameters indicate that pressure has little effect on the topologyof the CaO–SiO₂, CaMgSi₂O₆–SiO₂, and CaMgSi₂O₆–Mg₂SiO₄systems but a pronounced one on the MgO–SiO₂ binary. Themost striking change concerns passage of the MgSiO₃ phase fromperitectic melting at 1 bar to eutectic melting at 1·0GPa. This transition is estimated to occur at 0·41 GPa.For the CaMgSi₂O₆–SiO₂ and CaMgSi₂O₆–Mg₂SiO₄ pseudo-binaries,the size of the field clinopyroxene + liquid increases withincreasing pressure. This change is related to the shift ofthe piercing points clinopyroxene + silica + liquid (from 0·375mol fraction SiO₂ at 1 bar to 0·414 at 1·0 GPa)and clinopyroxene + olivine + liquid (from 0·191 molfraction SiO₂ at 1 bar to 0·331 at 1·0 GPa) thatbound the clinopyroxene + liquid field in the CaMgSi₂O₆·SiO₂and CaMgSi₂O₆·Mg₂SiO₄ pseudo-binaries, respectively. KEY WORDS: CaO–SiO₂; CaMgSi₂O₆–Mg₂SiO₄; CaMgSi₂O₆–SiO₂; experiments; MgO–SiO₂