Phase equilibria in the MgO–SiO2–ZrO2 system

Resumo

The results of study of phase equilibria in the MgO–SiO₂–ZrO₂ system at 1450–1550°C are reported. The studied system contains two eutectic points and six fields: (I) MgSiO₃ + SiO₂; (II) MgSiO₃ + ZrO₂; (III) ZrSiO₄ + SiO₂; (IV) MgSiO₃ + Mg₂SiO₄; (V) ZrO₂ + MgO; (VI) ZrSiO₄ + ZrO₂. The presence of fields (II) and (III) on the diagram shows that zircon in equilibrium with olivine and pyroxene crystallizes at very low concentrations of ZrO₂ in the system. This provides a solution for one of the most important problems in zirconology of dunites: the probability of the formation and preservation of zircon in the course of the formation and evolution of dunite.