Contributions to Mineralogy and Petrology

, Volume 146, Issue 4, pp 450–462 | Cite as

An experimental study of phase equilibria in the systems H2O–CO2–CaCl2 and H2O–CO2–NaCl at high pressures and temperatures (500–800 °C, 0.5–0.9 GPa): geological and geophysical applications

  • Kirill I. Shmulovich
  • Colin M. GrahamEmail author
Original Paper


Phase equilibria in the ternary systems H2O–CO2–NaCl and H2O–CO2–CaCl2 have been determined from the study of synthetic fluid inclusions in quartz at 500 and 800 °C, 0.5 and 0.9 GPa. The crystallographic control on rates of quartz overgrowth on synthetic quartz crystals was exploited to prevent trapping of fluid inclusions prior to attainment of run conditions. Two types of fluid inclusion were found with different density or CO2 homogenisation temperature (Th(CO2)): a CO2-rich phase with low Th(CO2), and a brine with relatively high Th(CO2). The density of CO2 was calibrated using inclusions in the binary system H2O–CO2. Mass balance calculations constrain tie lines and the miscibility gap between brines and CO2-rich fluids in the H2O–CO2–NaCl and H2O–CO2–CaCl2 systems at 500 and 800 °C, and 0.5 and 0.9 GPa. The miscibility gap in the CaCl2 system is larger than in the NaCl system, and solubilities of CO2 are smaller. CaCl2 demonstrates a larger salting-out effect than NaCl at the same P–T conditions. In ternary systems, homogeneous fluids are H2O-rich and of extremely low salinity, but at medium to high concentrations of salts and non-polar gases fluids are unlikely to be homogeneous. The two-phase state of crustal fluids should be common. For low fluid-rock ratios the cation compositions of crustal fluids are buffered by major crustal minerals: feldspars and micas in pelites and granitic rocks, calcite (dolomite) in carbonates, and pyroxenes and amphiboles in metabasites. Fluids in pelitic and granitic rocks are Na-K rich, while for carbonate and metabasic rocks fluids are Ca-Mg-Fe rich. On lithological boundaries between silicate and carbonate rocks, or between pelites and metabasites, diffusive cation exchange of the salt components of the fluid will cause the surfaces of immiscibility to intersect, leading to unmixing in the fluid phase. Dispersion of acoustic energy at critical conditions of the fluid may amplify seismic reflections that result from different fluid densities on lithological boundaries.


Fluid Inclusion Quartz Overgrowth Lithological Boundary Oxalic Acid Dihydrate Silver Oxalate 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We thank Bruce Yardley for regular discussions and the use of heating–freezing stage facilities at the University of Leeds; Steve Elphick and Bob Brown for laboratory and workshop support and advice; Sergei Zatsepin for discussion of the interpretation of mechanisms of seismic reflection. Helpful reviews by John Holloway and Ian Parsons are gratefully acknowledged. This study was supported by NERC Research Grant GR3/12910.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.School of Geo SciencesUniversity of EdinburghEdinburgh UK
  2. 2.Institute of Experimental MineralogyRussian Academy of SciencesMoscowRussia

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