Earth and Planetary Sciences Faculty and Staff Publications

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Eclogite, constituting the subducted crust, is one of the most important geochemical and geophysical heterogeneities in the Earth’s mantle. As the dominant anisotropic phase in eclogite, precise high pressure-temperature single-crystal elastic properties of omphacite provides the basis for detecting eclogite in the Earth’s upper mantle. In this study, we measured the single-crystal elastic moduli of omphacite up to 18 GPa and 700 K using Brillouin spectroscopy. A least-squares fit to a third-order finite strain equation of state yields KS0’=4.5(1), G0’=1.53(5), ∂KS0/∂T=-0.029(5) GPa/K, ∂G0/∂T=-0.013(5) GPa/K, with ρ0=3.34(1) g/cm3, KS0=123(3) GPa, and G0=74(2) GPa. We found that the seismic velocities of eclogite are similar to pyrolite at the depths of 200-300 and 410-500 km, thus eclogite is seismically invisible at these depths. Combined with the lattice-preferred orientations of the omphacite in naturally deformed eclogites, we also modeled seismic anisotropy of eclogite at various pressure-temperature conditions.