The graduate program in Aqueous Geochemistry at the University of Minnesota investigates all aspects of fluid-rock interaction and hydro-geochemistry in terrestrial and submarine environments. The approach we use is highly interdisciplinary and involves laboratory, field and theoretically-based studies of the effects of inorganic and organic processes on the chemical evolution of aqueous fluids in natural systems. Importantly, the linkage between geochemical, geophysical, hydrological, and microbiological processes has been a long standing area of interest and represents a common theme in all of our research. 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, links directly to our field programs, but the research represents stand-alone investigations of many fundamental aspects of environmental aqueous geochemistry. Presently active field and lab-based research projects in aqueous geochemistry at the University of Minnesota are briefly described as follows:
Field Studies of Hydrothermal Venting in Submarine and Subaerial Settings
Seafloor hydrothermal systems have played a key role in controlling the chemistry of seawater in the modern and ancient ocean, while providing chemicals that fuel microbial ecosystems at deep sea vents. The figure to the left shows sampling of hydrothermal vent fluids with ROV (Remotely Operated Vehicle) Jason II at the Rainbow hydrothermal field (36°N, Mid-Atlantic Ridge) by University of Minnesota scientists and students. This research is being carried out in collaboration with a highly diverse group of scientists associated with academic and federal agencies. In addition to direct sampling and analysis of hydrothermal vent fluids (see above), the aqueous geochemistry group 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.
Continental hydrothermal systems have immense scientific and practical significance and are critically important to the Earth’s thermal budget and geochemical cycles. They are of great interest because they are a primary source of economically important metal deposits, constitute geothermal resources, and support exotic ecosystems that have only recently been discovered. However, the subsurface conditions and processes that control these systems are poorly understood because they entail the flow of multi-phase and multi-component fluids through rocks with highly transient and heterogeneous permeabilities, and are perturbed by a multitude of geological and environmental processes. Our research in this area is focused on understanding controls on heat and mass transfer processes responsible for hydrothermal venting on from the floor of Yellowstone Lake. Yellowstone Lake is the is the largest high altitude lake in North America. Although Yellowstone National Park is famous for abundant and spectacular hydrothermal activity, recent geochemical and geophysical studies indicate the existence of hundreds of hydrothermal vents on the lake floor, issuing fluids with high concentrations of elements including: As, B, Li, Hg, Mo, CO2, and H2S. Our investigation of Yellowstone Lake vents is part of the NSF funded Hydrothermal Dynamics of Yellowstone Lake (HD-YLake) project. This interdisciplinary project uses geophysical and geochemical instrumentation to study how the lake floor hydrothermal vents respond to tectonic, magmatic, and climatic processes.
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, Zn, and S are presently being studied with support from the National Science Foundation.
- 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 system with and without mineral catalysts provide constraints 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 meteorites 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 and fluid-mineral systems 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, funded by the National Science Foundation, more accurately simulate the natural system and therefore provide solubility data to further our understanding of the chemical reactions occurring at depth at mid-ocean ridges, as well as in subareal hydrothermal systems. The solubility data also provide us the data necessary to begin to create a theoretical framework for fluids at such extreme P-T conditions.