ELECTRICAL-CONDUCTIVITY OF SILICATE PEROVSKITE AT LOWER-MANTLE CONDITIONS

Geophysical models of the electrical conductivity of the Earth's mantl e based on the observed variations of electric and magnetic fields at the surface of the Earth yield estimates of about 1 S m(-1) for the co nductivity of the uppermost lower mantle(1,2). But laboratory conducti vity measurements on silicate perovskite (thought to be the dominant c onstituent of the lower mantle) at high pressures have given conflicti ng estimates of mantle conductivity, ranging from less than 10(-5) up to 1 S m(-1) (refs 3-6). Here we present measurements of the electrica l conductivity of perovskite in a multi-anvil press at conditions appr opriate for the uppermost lower mantle (pressures up to 23 GPa and tem peratures up to 2,000 K). We find that the geophysical estimate of low er-mantle electrical conductivity can be well explained by the conduct ivity of the perovskite component of a low-oxygen-fugacity mantle comp osed of pyrolite(7) (the assemblage of mineral phases thought to broad ly represent that of the Earth's mantle), assuming a standard geotherm . Our results also indicate that the temperature dependence of perovsk ite conductivity at lower-mantle temperatures and pressures is signifi cantly larger than shown previously; extrapolations of low-temperature conductivity measurements to the higher temperatures of the lower man tle should therefore be treated with caution.