[S-IT39_2PO1] 地球深部ダイナミクス：プレート・マントル・核の相互作用

[SIT39-P09] 放射光X線その場観察と川井式マルチアンビル装置を用いた30 GPaまでのクロム苦土鉱の相関係の解明

*國本 健広¹、入舩 徹男¹、藤野 清志¹ (1.愛媛大学)

キーワード：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.