Effect of iron content on electrical conductivity of ringwoodite, with implications for electrical structure in the transition zone

摘要: Abstract Electrical conductivity of ringwoodite with various iron contents [Fe/(Fe + Mg) = 0.09, 0.2 and 0.3] was measured at pressure (20 GPa) temperature (up to 1900 K) conditions the lower part mantle transition zone in a Kawai-type multi-anvil apparatus. The increased increasing total content. All electrical data were fitted formula σ = σ0 XFe exp(−H/kT), where σ0 is pre-exponential term, XFe mole fraction content Mg site, H activation enthalpy, k Boltzmann constant T absolute temperature. enthalpy becomes higher certain At high temperatures, decreased from 1.44 0.92 eV Fe low temperatures less than 1000 K, also decreases 1.15 0.74 eV Dependence on suggests that dominant mechanism charge transport Fe2+–Fe3+ hopping (small polaron). Recent conductivity-depth profiles beneath Pacific Ocean obtained electromagnetic induction study shows values between 520 660 km depths may be explained by Fe/(Fe + Mg) = 0.10. On other hand, assuming normal geotherm, continent or stable craton are considerably those Taking into consideration results global seismic tomographic studies, relatively these regions can existence cooler region compared surrounding mantle, rather presence iron-poor ringwoodite, combination both.