HR: 0800h
AN: B21A-1011    [Abstracts]
TI: Cool CO₂ Springs of the Western U.S.: Continental "Smokers"?
AU: * Crossey, L J
EM: lcrossey@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Karlstrom, K E
EM: kek1@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Newell, D L
EM: dnewell@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Kirk, M L
EM: mfkirk@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Takacs-Vesbach, C
EM: cvesbach@unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131 United States
AU: Dahm, C N
EM: cdahm@sevilleta.unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131 United States
AU: Fischer, T
EM: fischer@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Hilton, D
EM: drhilton@ucsd.edu
AF: Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0244 United States
AB: CO2 springs found in association with extensional basins of the western U.S. are often associated with extensive Quaternary travertine and lacustrine carbonate deposits, reflecting a long-lived interaction of deeply-sourced, "endogenic" fluids with the surficial hydrologic regime. These systems can be thought of as continental analogues to the rich chemolithotrophic microbial ecosystems found in oceanic extensional tectonic settings (hydrothermal systems associated with mid-ocean ridges). We use a variety of geochemical tracers (aqueous and gas) in active systems to trace the origins of the CO2-rich waters. Major ion chemistries allow for the development of regionally-consistent mixing models. Mixing models using Cl vs. Cl/Br and Sr vs. 87/86-Sr indicate only a small component of saline, radiogenic, hydrothermal fluid is needed to produce the observed spring chemistries. Analysis of dissolved gases within the spring waters also reveals a mixing trend between atmosphere/soil gas with an end-member dominated by CO2 (high CO2/N2) ; gas compositions range to over 99 volume % CO2 in some springs. Hydrogen concentrations are consistently in the 100s of nannomolar range, and methane and hydrogen sulfide are detected in several springs. Trace gas analyses shows elevated He concentrations (low N2/He) suggestive of a deep crustal or mantle origin for the gases, linking them to magmatism and extensional tectonics. Isotopes of helium and carbon in the spring gases are consistent with a significant mantle-derived component. The CO2 richness coupled with the presence of hydrogen and a suite of redox-sensitive trace components offer a chemically rich setting for a diverse microbial community. When extensional faults serving as the conduits for endogene fluids encounter typical basin fill associated with many extensional basins (e.g., Rio Grande Rift, Basin and Range, Arizona transition zone, etc.), these fluids are mixed with the shallow hydrologic system, resulting in aquifer waters with similar geochemical character to springs. We anticipate that ongoing microbial community analysis will reveal the presence of microorganisms utilizing many of the same metabolic pathways found in oceanic hydrothermal settings.
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
DE: 1051 Sedimentary geochemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005