View article

NaCl is the most common solute in aqueous fluids in many geological settings but the thermodynamic properties of binary NaCl–H₂O solutions have remained understudied at pressures above 0.5 GPa. We report the first high-pressure (>0.5 GPa) density data for NaCl–H₂O fluids derived from acoustic velocity measurements in 1m and 3m NaCl solutions in diamond anvil cells to 673 K and 4.5 GPa using Brillouin scattering spectroscopy. An empirical equation of state (EoS) for NaCl–H₂O fluids has been generated fitting the new density data together with literature data for water, and used for extrapolation of thermodynamic data to 1073 K and 4.8m NaCl at 0.5–4.5 GPa, spanning the conditions for fluids expelled by subducted slabs. The EoS yields densities for binary NaCl–H₂O solutions with uncertainty lower than 0.3–0.5% below 673 K and lower than 2–4% in the extrapolation region. The EoS may allow …