Electrical conductivity of silicate perovskite at lower-mantle conditions

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Geophysical models of the electrical conductivity of the Earth's mantle based on the observed variations of electric and magnetic fields at the surface of the Earth yield estimates of about 1 S m sup -1 for the conductivity of the uppermost lower mantle [1,2]. But laboratory conductivity measurements on silicate perovskite (thought to be the dominant constituent of the lower mantle) at high pressures have given conflicting estimates of mantle conductivity, ranging from less than 10-5 up to 1 S m-1[3-6]. Here we present measurements of the electrical conductivity of perovskite in a multi-anvil press at conditions appropriate for the uppermost lower mantle (pressures up to 23 GPa and temperatures up to 2,000 K). We find that the geophysical estimate of lower-mantle electrical conductivity can be well explained by the conductivity of the perovskite component of a low-oxygen-fugacity mantle composed of pyrolite [7] (the assemblage of mineral phases thought to broadly represent that of the Earth's mantle), assuming a standard geotherm. Our results also indicate that the temperature dependence of perovskite conductivity at lower-mantle temperatures and pressures is significantly larger than shown previously; extrapolations of low-temperature conductivity measurements to the higher temperatures of the lower mantle should therefore be treated with caution.

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