Phases and electrical conductivity of a hydrous silicate assemblage at lower-mantle conditions

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Abstract

THE presence of a small amount of water in the lower mantle might affect in a significant way the geophysical and geochemical properties of its host mineral assemblage1–5. Here we present experimental observations of the phase behaviour and the electrical conductivity of a hydrous silicate assemblage synthesized from a mixture of (Mg0.88Fe0.12)SiO3 pyroxene and water under the pressure and temperature conditions of the lower mantle. Previous studies have shown that anhydrous (Mg, Fe)SiO3 pyroxene transforms to a perovskite structure under these conditions6–9. We find that, although the hydrous assemblage is also dominated by the (Mg, Fe)SiO3 perovskite phase, it coexists with the so-called hydrous phase D, of estimated composition (Mg, Fe)SiH2O4. Our measurements show that the inclusion of small amounts of water in the silicates can enhance the electrical conductivity of the lower-mantle assemblage by more than three orders of magnitude at these temperatures and pressures.

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Li, X., Jeanloz, R. Phases and electrical conductivity of a hydrous silicate assemblage at lower-mantle conditions. Nature 350, 332–334 (1991) doi:10.1038/350332a0

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