The influence of pressure on the hydrogen-assisted electrical conductivity in olivine has been studied under conditions of 4-10 GPa and 873-1273 K. Synthetic polycrystalline olivine samples with the water content of 160 ppm wt (Paterson calibration) were used and the electrical conductivity was determined from the results of the impedance spectroscopy. We found that the pressure reduces the hydrogen-assisted electrical conductivity, but its magnitude is small: between 4 and 10 GPa, the difference is a factor of similar to 2.5 for the same water content and temperature. The pressure dependence is characterized by a negative activation volume and the negative dependence of the pre-exponential factor on pressure. Such anomalous behavior is explained by a model where hydrogen-related defect is considered as a weak inclusion in a strong matrix.

We use these new data to calculate the electrical conductivity contrast at the 410-km discontinuity. We found that if the water content of the mantle does not change with depth, there should be a large (a factor of similar to 10) drop in conductivity from above to below the 410-km discontinuity. In contrast, geophysically inferred electrical conductivity increases at 410-km suggesting the increase in water content from above to below the 410-km discontinuity.

The present results are used to compare several previous results obtained at different pressures. It was shown that our results agree well with most of previous studies but not with (Yoshino et al., 2009). Possible causes for this discrepancy are discussed. (C) 2014 Elsevier B.V. All rights reserved.