[S-IT39_2PO1] Deep Earth science: Dynamics of plate, mantle, and core

[SIT39-P09] In situ X-ray observations of phase transitions in MgCr2O4 to 30 GPa using Kawai-type multianvil apparatus

*Takehiro KUNIMOTO¹, Tetsuo IRIFUNE¹, Kiyoshi FUJINO¹ (1.Ehime University)

Keywords:Magnesiochromite, in situ X-ray diffraction measurement, Kawai-type multianvil apparatus, phase transition

Phase relations in MgCr₂O₄ (magnesiochromite) have been studied up to 30 GPa and 1600℃, using a large volume Kawai-type multianvil apparatus and in situ X-ray diffraction measurements system installed at SPring-8/BL04B1. MgCr₂O₄ spinel dissociates into Mg₂Cr₂O₅ (orthorhombic type) + Cr₂O₃ (eskolate) at 9 GPa and 1200℃, and then reunion to higher pressure phase (CaTi₂O₄ type) at 22 GPa and 1200℃. Moreover, another high-pressure phase was observed above CaTi₂O₄ type structure phase, and this phase was unquenchable to ambient condition. In addition, pressure-induced phase transition in MgCr₂O₄ was confirmed without decomposition under cold compression process. In this cause, Magnesiochromite is directly transformed to high-pressure phase through the mixture of spinel and high-pressure phase. In this study, CaFe₂O₄ type and ε-phase, which reported in earlier studies in MgAl₂O₄ were not observed. The Birch-Murnaghan equation of state was used for least-squares fitting of the volume data (assuming K₀’=4). Thus, determined zero-pressure bulk modulus (K₀) of the CaTi₂O₄ type MgCr₂O₄ was 195 GPa. In this presentation, we will discuss further details of high-pressure phase relation and physical properties of high-pressure phases in MgCr₂O₄ series.