The Effect of Water on Ionic Conductivity in Olivine

High-temperature ionic conductivity in olivine single crystals has been measured in the [100], [010], and [001] crystallographic orientations as a function of pressure from 2 to 10 GPa, temperature from 1450 to 2180 K, and H2O content from 20 to 580 wt. ppm using multianvil presses with in situ impedance analyses. The experimental results yield an activation energy, activation volume, and H2O content exponent of 250-405 kJ/mol, 3.2-5.3 cm(3)/mol, and 1.3 +/- 0.2, respectively, for the high-temperature ionic conduction regime. Olivine ionic conductivity has negative pressure and positive temperature dependences and is significantly enhanced by H2O incorporation. The [001] direction is more conductive than the [100] and [010] directions. The H2O-enhanced ionic conductivity may contribute significantly to the electrical conductivity profile in the asthenosphere, especially in the regions under relatively high-temperature and low-pressure conditions.