Experimental Determination of Phase Equilibria and Thermodynamic Properties of the System H2O-CO2-NaCl

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Anovitz and LabotkaEAR-0106990Aqueous fluids in the Earth's crust participate in nearly all geologic processes, including partial melting, heat and solute transport, reaction and alteration of host country rock, deposition of insoluble minerals in fractures, and rock deformation. The extent to which fluid participates in these processes depends on its chemical and transport properties. The H2O-CO2-NaCl system is a close approximation to real crustal fluids. An understanding of the p-V-T-x properties of this system is critical, and an experimental determination of the thermophysical properties at high temperatures and pressures is clearly required to be able to understand the fluid-rock interaction in crustal geologic processes. We, in collaboration with J. Blencoe, propose to determine experimentally the phase relations and thermodynamic properties of the H2O-CO2-NaCl system at pressures ranging from 100 to 300 MPa and temperatures from 500 to 800 degrees C. These conditions lie above the critical curve of the H2O-CO2 binary, span the critical curve in the H2O-NaCl binary, and are appropriate for many crustal fluid-rock processes. We will determine the halite saturation surface and the activities of H2O on the surface with the use of an internally heated pressure vessel equipped with hydrogen service. With these data, we will be able to determine the phase equilibria and the activity-composition relations for the ternary system. The results will be complementary to studies of the system that use synthetic fluid inclusions and will provide the basic input necessary to construct mathematical models of the thermodynamics of the H2O-CO2-NaCl system at conditions appropriate for crustal geothermal, metamorphic, and deformation systems.