[S-IT14] Deep Earth Sciences

[SIT14-P16] The stability of CaMgSi₂O₆ cubic perovskite under high-pressure and high-temperature

*Kotaro Nakamura¹, Masayuki Nishi¹, Sho Kakizawa², GREAUX STEEVE GEORGI³, Noriyoshi Tsujino², Tadashi Kondo¹ (1.Osaka University, 2.Japan Synchrotron Radiation Research Institute, 3.Ehime University Geodynamics Research Center)

Keywords:CM-perovskite, in situ X-ray diffraction measurements, multi-anvil apparatus

The lower mantle of the Earth is known to consist of three types of minerals: bridgmanite (MgSiO₃), periclase (MgO), and davemaoite (CaSiO₃). A recent experimental study using diamond anvil cells has reported that a significant amount of Ca component can be incorporated into bridgmanite, suggesting the disappearance of davemaoite in the high-temperature and high-pressure conditions above 40 GPa and 2300 K (Ko et al., 2022, Nature). On the other hand, previous experimental studies have reported that CM-perovskite (CaMgSi₂O₆) appears temporarily as a metastable phase during the high-pressure phase transition from diopside to the equilibrium phase assemblage of bridgmanite and davemaoite under the lower mantle conditions. Here, we conducted high-temperature and high-pressure experiments using a multi-anvil apparatus to understand the conditions such as the pressure, temperature, time, and chemical compositions to form CM-perovskite. In situ X-ray diffraction measurements under high-temperature and high-pressure were performed using a multi-anvil apparatus SPEED-Mk.Ⅱ, installed at BL04B1, SPring-8. We used sintered diamond anvils to achieve pressures up to 42 GPa, and temperatures up to 2100 K. Starting materials were glasses with compositions of CaMgSi₂O₆, Ca_0.95Mg_0.95Al_0.2Si_1.9O₆ and natural diopside (below 1 wt.% Al and Fe). We obtained the XRD patterns identical to CM-perovskite under high-temperature and high-pressure conditions. In this presentation, we discuss the chemical composition and occurrence conditions of this phase based on the obtained results.