Electrical conductivity of hydrous natural basalts at high temperatures and pressures

• Electrical conductivities of hydrous natural Fe-bearing basalt were determined.
• Dominant conduction mechanism in samples is proposed to be proton conduction.
• A general conductivity formula was established as a function of water content.

The electrical conductivities of natural iron-bearing basalts, with a water content ranging from 0.62 to 4.19 wt.%, were determined for a range of pressure (0.5–2.0 GPa) and temperature (823–1173 K) conditions. A Ni–NiO solid oxygen buffer was selected to stabilize the oxygen partial pressure. Increasing pressure causes the electrical conductivity of the hydrous sample to slightly decrease, whereas the activation enthalpy increases. The activation energy and activation volume are 0.86 ± 0.14 eV and 1.43 ± 0.25 cm3/mol, respectively. At a constant pressure of 2.0 GPa, the electrical conductivity increases with increasing water content. Considering the dependence of activation enthalpy on water content for all samples at 2.0 GPa, the electrical conductivity data were fitted to the formula σ=A1+A2*Cwγ*exp−ΔH0−αCwβRT, where A1 and A2 is the pre-exponential factor, CW is the water content in sample, ΔH0 is the activation enthalpy at very low water concentrations, T is the absolute temperature, k is the Boltzmann constant, and r, α and β are constants. Furthermore, the electrical conductivity of natural hydrous basalts cannot account for the crustal high-conductivity anomaly observed in magnetotelluric results observed in the North China Craton, Axial Volcanic Ridge, and Transverse Electric models.