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.
Fluids play an important role in many geologic processes, including the formation of petroleum and mineral deposits, the triggering of earthquakes and volcanic eruptions, and transporting heat through the earth's crust. In order to predict the extent to which these fluid-assisted processes influence the evolution of the earth, detailed quantitative information concerning the properties of natural fluids over the complete range of temperature, pressure and fluid composition conditions encountered in crustal environments is required. One of the best methods available to determine the role of fluids in natural environments is through the study of fluid inclusions, which are small droplets of fluid or melt that are trapped in minerals when they form at great depths in the earth (See Figure). Complete and accurate interpretation of data obtained from fluid and melt inclusions requires information on the properties of these fluids at high temperatures and pressures. Natural brines rich in sodium and calcium chloride salts are common in may sedimentary basins that occur on the continents. These basins host many of the petroleum and natural gas deposits being produced for energy, as well as mineral deposits for lead, zinc, copper and other metals. In this study we have determined the properties of H2O-NaCl-CaCl2 fluids and have developed a numerical model that can be used to interpret results obtained from fluid inclusions formed in these environments. This, in turn, allows workers to develop more accurate models to explore for resources in sedimentary basins. Sedimentary basins are also considered to be one of the best sites for the long-term storage of carbon dioxide produced by burning of fossil fuels. However, little is known about the long-term behavior of the subsurface reservoirs following CO2 injection. In this project we developed a technique to accurately determine the salinity of fluid inclusions containing brines and carbon dioxide. This method allows us to better characterize the compositions of fluids in sedimentary environments containing high salinity brines and carbon dioxide. One of the most important factors controlling the nature of volcanic eruptions is the composition and amount of gases contained in the magma body beneath a volcano. One of the best techniques to determine the gas (volatile) content of magmas is to study melt inclusions that are trapped in the magma chamber before the eruption. In this project we developed a quantitative model that describes how the volatile composition of melt inclusions evolves after the melt is trapped at depth and during the subsequent eruption. These data are critical to develop a better understanding of the mechanisms and processes associated with explosive volcanic eruptions, such as the 1980 Mt. Saint Helens eruption and the one that destroyed Pompeii in 79 AD.
