Single‐Crystal Elasticity of Phase E at High Pressure and Temperature: Implications for the Low‐Velocity Layer Atop the 410‐km Depth

Dense hydrous magnesium silicate (DHMS) phase E is a potential water carrier in subducting slabs that can transport to the Earth's deep mantle between bottom of upper and uppermost transition zone. Therefore, knowledge on high pressure‒temperature (P‒T) full elastic moduli at relevant conditions important deciphering existence DHMS phases their influences seismic profiles region; however, P‒T elasticity data still remains lacking. In this work, we determined combined effect single-crystal up 24 GPa 900 K by situ X-ray diffraction Brillouin scattering measurements externally-heated diamond anvil cells. The aggregate compressional-wave (VP) shear-wave (VS) velocities are then derived analyzing density using third-order finite-strain equations. We found exhibits much lower bulk shear acoustic than most abundant constituent minerals zone, such as olivine, clinopyroxene, garnet, wadsleyite. modeled results obtained show hydrated pyrolite model result relatively Vp Vs negative velocity anomalies observations. with could be possible origin low-velocity layers atop 410-km discontinuity some cold highly-hydrated regions.