[S-IT03] Structure and dynamics of Earth and Planetary deep interiors

[SIT03-11] First principles study on the phase stability and elasticity of potassium-host hexagonal aluminous phases

*河合 研志¹、土屋 卓久² (1.Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, University of Tokyo、2.Geodynamics Research Center, Ehime University)

キーワード：High pressure, Pottasium, Lower mantle, Aluminous phase

In order to understand the fate of the potassium-bearing phase subducted into the deep Earth's interior, we have studied the high-pressure stability and elasticity of KMg2Al5SiO12 hexagonal aluminous phase (K-Hex) by means of the density functional computation method. The K-Hex phase is found to be mechanically stable up to 150 GPa and also energetically more stable than the calcium-ferrite (K-CF) type structure up to 150 GPa. In addition, calculations indicate that when the spinel composition coexists with the K-hollandite (K-Hol) phase, the K-Hex phase becomes more stable than the K-Hol phase at pressures above ~27 GPa. This suggests that the hexagonal aluminous phase be a potential host of the incompatible large-ion elements such as potassium in the lower mantle, especially in the subducted basaltic Mg and Al rich composition. Finally, seismic velocities of the K-Hex phase are found slower than Mg-perovskite (pv) in the lower mantle pressures, while its density is larger than Mg-pv over 70 GPa.