Single-crystal elasticity of phase Egg AlSiO3OH and δ-AlOOH by Brillouin spectroscopy

Abstract

Phase Egg and δ-AlOOH are two typical hydrous phases that might exist in the wet sedimentary layer of subducted slabs under mantle conditions. They are thus regarded as potential water carriers to Earth's deep mantle. In this letter, we report the full elastic constants of both phases determined by Brillouin scattering and X-ray diffraction measurements under ambient conditions. Our results indicate that the hydrogen-bond configurations in the crystal structures of the two phases have a profound effect on their principal elastic constants. The adiabatic bulk modulus (K S ) and shear modulus (G) calculated from the obtained elastic constants using the Voigt-Reuss-Hill averaging scheme are 158.3(201) GPa and 123.0(60) GPa for phase Egg and 162.9(31) GPa and 145.2(13) GPa for δ-AlOOH, respectively. These results allow us to evaluate elastic moduli and sound velocities of hydrous minerals in the Al 2 O 3 -H 2 O-SiO 2 ternary system (simplified composition of subducted wet sedimentary layer) at ambient conditions including the contrast of the acoustic velocities V P and V S for the reaction production AlSi 3 OH=δ-AlOOH+SiO 2 (stishovite) and the evolution in the elastic moduli and sound velocities of hydrous minerals as a function of density.

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

“…The DHMS phases have a relatively high‐water content and hydrogen bonds in their crystal structures in comparison with the nominally anhydrous minerals of the constituent mantle phases. The high‐water content in the DHMS phases contributes to their unique physical properties including the sound velocities and rheology (Mookherjee & Tsuchiya, 2015; Tsuchiya & Tsuchiya, 2008; Wang et al., 2022). Thus, determining the elastic properties of the DHMS phases, particularly at the high P‒T conditions of the mantle is important to decipher the related seismic anomalies, to evaluate the potential storage sites, distribution and circulation of water in subduction zones and to deepen our understanding of the subduction‐related geochemical and geodynamic processes (Duan et al., 2018; Karato, 2011; Karato et al., 2020; Li et al., 2016; Rosa et al., 2012; Xu et al., 2020).…”