Accomplishment Based Renewal: Experimental Studies of the PTX Properties of Immiscible Fluids at Crustal PT Conditions

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Intellectual merit: Immiscibility (boiling) in fluids approximated by the H2O-CO2-NaCl-KCl- CaCl2 system is common in many crustal environments, including epithermal precious metals deposits, porphyry copper-gold-molybdenum deposits, metamorphic lode gold deposits and other crustal igneous and metamorphic environments. Fluid immiscibility is an effective mechanism for partitioning and concentrating certain elements into one or the other of the two coexisting phases and thus plays an important role in crustal geochemical processes. Fluid inclusions provide the best evidence for the occurrence of fluid immiscibility in these environments, but our ability to interpret microthermometric and microanalytical data from natural inclusions is limited by the lack of experimental PTX data on compositions of coexisting fluids at crustal pressure-temperature (P-T) conditions. Experiments will be conducted using the synthetic fluid inclusion technique to determine compositions of coexisting fluids in the H2O-CO2-NaCl, H2O-NaCl-KCl and H2O-NaCl-CaCl2 ternary subsystems. The P-T limits of immiscibility will be defined based on observations of synthetic fluid inclusions trapped at known conditions. Fluid inclusions trapped in the one-phase fluid field all show identical room temperature phase relations and microthermometric behavior. Those trapped in the two-phase field show a bimodal distribution of phase behavior, indicative of the liquid and vapor phases that were present at elevated temperature and pressure. Compositions of the coexisting liquid and vapor phases will be determined from microthermometric analyses, interpreted using previously determined data for the appropriate fluid system, and supplemented by Raman spectroscopy to identify daughter minerals and to determine the H2O/CO2 ratio of CO2-bearing inclusions. The proposed research represents a continuation of ongoing experimental efforts designed to provide fundamental PVTX data on geologically-relevant fluids so that we may better understand the critical role that fluids play in the geochemical and rheological evolution of the crust and upper mantle. Broader impact: Funding provided by this grant will provide training for graduate students and help prepare them for successful careers in the earth sciences. This project will also support one or more undergraduate students each year to provide a meaningful research experience. The broader impacts also include lectures and workshops on Fluids in the Earth that the PI offers to students and professionals worldwide, as well as teaching introductory earth sciences courses to non-science majors at Virginia Tech. These activities reflect the broader impacts of the PI's research and the important role that quality undergraduate education plays in developing a scientifically literate society.