Equilibrium and metastable phase relations of the CaSiO 3 –MgSiO 3 system: formation and stability of CM-perovskite

We investigated phase relations in the CaSiO3–MgSiO₃ system through multi-anvil phase-equilibrium experiments and time-resolved in-situ X-ray diffraction measurements on diopside and related compositions. Under equilibrium conditions at 23–25 GPa and 2100 K, all starting materials decomposed into MgSiO₃ bridgmanite and CaSiO3 davemaoite. However, a (Ca,Mg)SiO3 CM-perovskite appeared transiently during the rapid decomposition of diopside in the in-situ XRD measurements. Its kinetic stability increased markedly at lower temperatures and higher pressures, and the phase was observed up to 2100 K at ∼40 GPa, indicating strong kinetic stabilization under high-pressure conditions. These results suggest that preservation of CM-perovskite found in a shocked meteorite requires extremely rapid quenching during the shock event. It also stresses that phase-equilibrium experiments – particularly at higher pressures than 40 GPa – must be interpreted carefully, as metastable perovskite compositions can readily appear during transformation processes.