[S-IT19] 地球深部科学

[SIT19-P13] Elasticity of Phase H under the Mantle Temperatures and Pressures: Implications for Discontinuities and Water Transport in the Mid-Mantle

*Zijun Song¹、Zhongqing Wu¹ (1.University of Science and Technology of China)

キーワード：phase H, elasticity, water transport, discontinuities

Dense hydrous magnesium silicates (DHMSs) are considered to be the main carriers for transporting water to the Earth’s interior. Phase H (MgSiO₄H₂), as one of the deepest forms of DHMSs, contains 15.3 wt% water and plays an important role in transporting water into the mid-mantle. In this work, we investigated the thermodynamic properties and elastic properties of phase H at high P-T conditions using first-principles calculations.
The dehydration of phase H into bridgmanite, which may occur at the depth of ~1300-1700 km in cold slabs, will cause an increase of 1.0%, 2.7%, 15% at 1500 km on V_P, V_s, and density, respectively. The impedance contrast for shear wave velocity by the dehydration of phase H is ~17%. Combining our results with seismic observations, the dehydration of the moderate amount of phase H could generate the seismic discontinuities at the depth of ~1300-1700 km detected in some subduction zones. Besides, the anisotropy of phase H is remarkable at the depths where phase H could exist stably and could be observed within slabs by seismology. Our results provide evidence for water transport in the mid-mantle.