The graduate program in Aqueous Geochemistry at the University of Minnesota investigates all aspects of fluid-rock interactions in terrestrial and submarine environments. The approach we use is inherently interdisciplinary and involves laboratory, field and theoretically-based studies. The figure below shows sampling of vent fluids with ROV (Remotely Operated Vehicle) Jason II at the Rainbow hydrothermal field (36°N, Mid-Atlantic Ridge) by UM scientists and students during a recent research cruise. Seafloor hydrothermal systems have played a key role in buffering ocean chemistry, while providing chemicals that have fueled microbial ecosystems, in the present and throughout geological time. Seafloor ore metal deposits (copper, zinc, gold) are also an important component of seafloor hydrothermal vents, and serve as a natural laboratory for the formation of similar deposits on land. Presently active research projects related to marine hydrothermal systems and other broader aspects of aqueous geochemistry are as follows:
Field Studies of Hydrothermal Venting in Submarine and Subaerial Settings
In addition to direct sampling and analysis of hydrothermal vent fluids (see above), the aqueous geochemistry group at UM has played a key role in the development of novel chemical sensors that can be used to monitor- directly and remotely- pH and redox of fluids issuing from hydrothermal vents on the seafloor. This work is supported by the National Science Foundation and entails submersible dives with DSV ALVIN to vents on the East Pacific Rise and Juan de Fuca Ridge. This research is being conducted in collaboration of Sr. Research Associate, Dr. Kang Ding.
Geochemical controls on the origin of dissolved gases and pH in hydrothermal vents throughout Yellowstone National Park and Yellowstone Lake, Wyoming has long been of interest to our group, especially since the overaching objectives are similar in many ways to our marine hydrothermal studies. This research is being carried out in collaboration with a highly diverse group of scientists associated with academic and federal agencies.
Lab Studies of Mineral and Fluid Reactions, Kinetics, and Isotope Exchange Processes
State of the art facilities for conducting process oriented research on chemical and isotope exchange between fluids and minerals exist in the Department of Earth Sciences at the University of Minnesota. In some cases, studies using these facilities link directly to our field programs described above, but the research represents stand alone investigations of many fundamental aspects of environmental aqueous geochemistry. Examples are as follows:
- The recent discovery that non-traditional stable isotopes can be measured accurately using state of the art analytical facilities underscores the need to experimentally calibrate the effects of temperature, pressure and composition on the partitioning of these isotopes between minerals and coexisting fluids, if these isotope systems are to fulfill their promise as process oriented tools in aqueous geochemistry. The non-traditional isotopes of Fe and S are presently being studied with support from the National Science Foundation. This research is being carried out in collaboration with Professor Shuhei Ono (MIT) and Professor David Borrok (UL-Lafayette).
- Investigations of geochemical controls on the abiotic hydrocarbon formation is an ongoing research activity in our lab. The cooling of reducing fluids in the C-H-O-S sysem with and without mineral catalysts provide contraints of the abiotic formation of organics in a wide range of geologic environments. This may have played a role in the origin of life on Earth, and may have been of importance to formation of organics on meterorites and other planetary bodies, such as Mars and Europa (moon of Jupiter).
- It has been recognized that seafloor hydrothermal vent fluids have dissolved chloride values that range from +/- 100% of the seawater source fluid. The variability in dissolved chloride provides evidence of phase separation in response to the intrusion of heat from magmatic bodies at relatively low hydrostatic pressures. The partitioning of chloride between coexisting vapor and brine gives rise to the distribution of metals and dissolved gases in ways that play a key role in hydrothermal alteration and heat and mass transfer processes. The application of flow-through hydrothermal experiments in fluid only systems, (in collaboration with Dr. Nick Pester (LBL)) has provided fundamental insight on this important problem in aqueous geochemistry. Currently, experiments are being performed to investigate the role pH, redox, pressure, and temperature on elemental partitioning between vapor and brine in fluid-mineral systems. These experiments more accurately mimic the natural system and will therefore provide solubility data to further our understanding of the chemical reactions occurring at depth at mid-ocean ridges. The solubility data also provide us the data necessary to begin to create a theoretical framework for fluids at such extreme P-T conditions.