P-V-T properties of fluids in the system H2O CO2 NaCl: New graphical presentations and implications for fluid inclusion studies Academic Article uri icon


  • Understanding the role of fluids in geologic processes requires a knowledge of the P-V- T properties of fluids over a wide range of conditions. Comparisons of several published equations of state with available experimental data for fluids composed of H2O and CO2 lead to the conclusion that the hard-sphere modified Redlich-Kwong equation of state of Kerrick and Jacobs (1981) most accurately predicts the P-V- T properties in this binary system. To model the volumetric properties in the H2OCO2NaCl system a formulation is presented involving a linear (ideal) interpolation between a pure-CO2 isochore predicted by the equation of state of Kerrick. and Jacobs (1981) and an H2O-NaCl isochore predicted by an empirical equation derived from the regression of available P-V-T data for the H2O-NaCl system. This formulation is applicable over a wide range of temperatures (>350C) and pressures (2-10 kbars) and is especially suitable for high pressures and low-to-moderate temperatures (fluid densities 1.0 cm3). Determination of the appropriate isochore for an H2OCO2NaCl fluid inclusion requires (1) the relative salinity (NaCl/H2O + NaCl), (2) bulk density of the combined gas and liquid CO2 phases, and (3) volume percent estimate of the aqueous p the total homogenization temperature. The commonly encountered problem of estimating the volume percents of phases in inclusions may be avoided in some applications, and several new P-X(CO2) diagrams have been constructed and contoured with (a) the solvi in the mixed volatile system and (b) the measured density of the CO2 phase. The effects of H2OCO2 clathrates during microthermometric observations in the laboratory are evaluated and in most instances can be minimized or avoided. Application of these results to fluid inclusion studies have led to improved determinations of (1) pressures and temperatures of fluid entrapment in a variety of geologic settings and (2) pressures and temperatures of cooling and uplift following the peak of metamorphism. Proper interpretation of fluid inclusion data (from the literature) for two granulite fades terranes suggests that the uplift P-T-t path is more nearly initially isobaric than has sometimes been presented. 1989.

published proceedings

  • Geochimica et Cosmochimica Acta

author list (cited authors)

  • Brown, P. E., & Lamb, W. M.

publication date

  • January 1, 1989 11:11 AM