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

Abstract

The elastic properties of Mg_(2.12(2))Fe_(0.21(2))Ni_(0.01)Si_(1.15(1))O_6H_(2.67(8)) phase E single crystals with Fe^(3+)/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): C_(11) = 192.2(6), C_(12) = 56.4(8), C_(13) = 43.5(8), C_(14) = –4.3(3), C_(33) = 192.1(7), C_(44) = 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 ν_P = 7.60(2) and ν_S = 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.

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