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Electrical Conductivity of NaCl‐Bearing Aqueous Fluids to 900 °C and 5 GPa
Author(s) -
Guo Haihao,
Keppler Hans
Publication year - 2019
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2018jb016658
Subject(s) - conductivity , electrical resistivity and conductivity , aqueous solution , analytical chemistry (journal) , dilution , molar conductivity , dissociation (chemistry) , dielectric , chemistry , materials science , thermodynamics , ion , chromatography , optoelectronics , electrical engineering , engineering , physics , organic chemistry
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‐H 2 O fluids up to 900 °C and 5 GPa are reproduced ( R 2 = 0.953) by a numerical model with log σ = −0.919 − 872.5/ T + 7.61 log ρ + 0.852 log c + log Λ 0 , 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/cm 3 ) at given pressure and temperature, and Λ 0 is the molar conductivity of NaCl in water at infinite dilution (in S·cm 2 ·mol −1 ), Λ 0 = 1,573 − 1,212 ρ + 537,062/ T – 208,122,721/ T 2 . 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.