In situ complex impedance spectroscopy of mantle minerals measured at 20 GPa and 1400 degrees C

Electrical conductivities of mantle silicate minerals (Mg0.9Fe0.1)(2)SiO4 o livine, wadsleyite and ringwoodite were determined at pressures up to 20 GP a and temperatures up to 1400 degrees C using complex impedance spectroscop y in a high pressure multianvil apparatus. All samples were polycrystalline , synthesized in separate high pressure experiments prior to the electrical measurements. Olivine conductivities up to 10 GPa are very close to values determined at ambient pressure under controlled oxygen fugacities in previ ous studies indicating a very small pressure dependence. The conductivities of wadsleyite at 15 GPa and ringwoodite at 20 GPa are similar, and both ab out 100 times greater than for olivine. When compared to conductivity model s of Earth's mantle, these results suggest that the steep increase in condu ctivity near the transition zone is mainly due to the olivine to wadsleyite phase transformation at 410 km depth, with only minor changes in conductiv ity occurring over the wadsleyite to ringwoodite transformation near 520 km depth.