Single-crystal elasticity of iron-bearing phase E and seismic detection of water in Earth's upper mantle

Abstract

The elastic properties of Mg2.12(2)Fe0.21(2)Ni0.01Si1.15(1)O6H2.67(8) phase E single crystals with Fe3+/ΣFe = 0.25(3) have been determined by Brillouin spectroscopy at ambient conditions. We find that that the elasticity of iron-bearing phase E is described by the six independent stiffness tensor components (all in units of GPa): C11 = 192.2(6), C12 = 56.4(8), C13 = 43.5(8), C14 = –4.3(3), C33 = 192.1(7), C44 = 46.4(3). The Voigt-Reuss-Hill averages of bulk and shear moduli are 95.9(4) and 59.6(2) GPa, respectively. The aggregate velocities of iron-bearing phase E are νP = 7.60(2) and νS = 4.43(1) km/s, markedly lower than those of major mantle minerals at ambient conditions. Modeling based on our results suggests that the presence of iron-bearing phase E may reduce the sound wave velocities in upper mantle and transition zone rocks, making it a possible target for future seismological investigations aiming to map hydration in subducting slabs.

Low Thermal Conductivity of Hydrous Phase D Leads to a Self‐Preservation Effect Within a Subducting Slab

“…Hsieh et al., 2018). Given the fact that the elastic moduli of other DHMSs, including phase A (Sanchez‐Valle et al., 2008), phase E (Satta et al., 2019; Shieh et al., 2000), and superhydrous phase B (D. Yang et al., 2017), are smaller or comparable to those of phase D (Y. Chang et al., 2013; Litasov et al., 2008), their thermal conductivities would follow such trend. This will strengthen our findings that the presence of poorly thermally‐conductive DHMSs would help maintain a low temperature condition within a subducting slab, forming a self‐protection mechanism for slab minerals to be transported to the deeper mantle.…”

“…Thermal conductivity of a material is positively correlated with its elastic moduli (Ashcroft & Mermin, 1976;W.-P. Hsieh et al, 2018). Given the fact that the elastic moduli of other DHMSs, including phase A (Sanchez-Valle et al, 2008), phase E (Satta et al, 2019;Shieh et al, 2000), and superhydrous phase B (D. Yang et al, 2017), are smaller or comparable to those of phase D (Y. Chang et al, 2013;Litasov et al, 2008), their thermal conductivities would follow such trend.…”

Topaz, a Potential Volatile-Carrier in Cold Subduction Zone: Constraint from Synchrotron X-ray Diffraction and Raman Spectroscopy at High Temperature and High Pressure

“…Furthermore, the dehydration occurs in the crust and the subducting lithosphere of the deep mantle, and it is mainly dependent on the stability of hydrous minerals in subduction zones [7][8][9][10]. Therefore, the structural stability and thermoelastic properties of hydrous minerals at high-pressure and high-temperature (high P-T) conditions are the keys to understanding the geodynamic processes in subduction zones [10][11][12][13][14][15][16].…”

Localized Anisotropy in the Mantle Transition Zone Due to Flow Through Slab Gaps

“…Atypical anisotropic minerals formed near or within the subducted slab may contribute to anisotropy. At relatively low mantle temperatures, two strongly anisotropic minerals, phase E and akimotoite, could form at transition zone depths (Hao et al., 2019; Satta et al., 2019). Phase E is a reaction product between olivine and water at upper transition zone depths (Satta et al., 2019).…”