The electrical conductivity of aqueous fluids containing 0.01, 0.1, and 1 M NaCl was measured in a piston‐cylinder apparatus up to 900 °C and 5 GPa. The conductivity generally increases with NaCl concentration, while the pressure and temperature effects are more complex. At 1–2 GPa, the effect of temperature on conductivity is small, while at higher pressures, conductivity increases with temperature. Pressure also enhances conductivity, but only above 300–400 °C. This effect may be due to enhanced ion dissociation in response to an increasing dielectric constant. However, at lower temperatures, conductivity decreases with pressure, probably due to an increase in fluid viscosity. The measured conductivities of NaCl‐H2O fluids up to 900 °C and 5 GPa are reproduced (R2 = 0.953) by a numerical model with log σ = −0.919 − 872.5/T + 7.61 log ρ + 0.852 log c + log Λ0, where σ is the conductivity in S/m, T is temperature in K, c is NaCl concentration in wt%, ρ is the density of pure water (in g/cm3) at given pressure and temperature, and Λ0 is the molar conductivity of NaCl in water at infinite dilution (in S·cm2·mol−1), Λ0 = 1,573 − 1,212 ρ + 537,062/T – 208,122,721/T2. We use our data to model the elevated electrical conductivity in the mantle wedge above subducted slabs. We find that due to the strong conductivity enhancement, in most cases less than one volume percent of aqueous fluid with moderate salinity is sufficient to explain the observed conductivity anomalies.

No abstract

No abstract