Elasticity and Anisotropy of the Pyrite-Type FeO2H-FeO2 System in Earth’s Lowermost Mantle
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The pyrite-type FeO2H-FeO2 system has been experimentally confirmed to be stable in Earth’s lowermost mantle but there is limited information about its physical properties at high pressures constraining our understanding of its potential geophysical implications for the deep Earth. Here, static calculations demonstrate that the pyrite-type FeO2H-FeO2 system has a high density and Poisson’s ratio and ultra-low seismic velocities at conditions of Earth’s lowermost mantle. It provides a plausible mechanism for the origin of ultra-low velocity zones at Earth’s D″ layer. The incorporation of hydrogen in the pyrite-type FeO2H-FeO2 system tends to decrease the S wave velocity (VS) but increase the bulk sound velocity (VΦ), and can potentially explain the observed anti-correlation of VS and VΦ in the lowermost mantle. Additionally, FeO2H exhibits nearly isotropic whereas FeO2 is highly anisotropic, which may help understand some seismic anisotropies at the core-mantle boundary.
Key WordsFeO2H FeO2 ultra-low velocity zones D″ layer anisotropy
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Xiang Wu and Shan Qin acknowledge financial support from the National Natural Science Foundation of China (Nos. 41473056 and 41472037). Thanks go to the reviewers and the editors for their helpful suggestions. The final publication is available at Springer via https://doi.org/10.1007/s12583-018-0836-y.
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