2006 Philadelphia Annual Meeting (22–25 October 2006)
Paper No. 192-5
Presentation Time: 9:25 AM-9:40 AM

CO2-RICH SPRINGS AND TRAVERTINES OF THE ROCKY MOUNTAIN REGION: MANTLE HELIUM ASSOCIATED WITH THE ASPEN ANOMALY AND GEOMICROBIOLOGY OF "CONTINENTAL SMOKERS”

CROSSEY, Laura J.1, KARLSTROM, Karl E.2, HILTON, David R.3, FISCHER, Tobias P.4, MITCHELL, Euan1, TAKACS-VESBACH, Cristina5, DAHM, Clifford N.6, and JACKSON-WEAVER, Olan6, (1) Earth & Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131, lcrossey@unm.edu, (2) Dept. of Earth & Planetary Sciences, Univ of New Mexico, Northrop Hall, Albuquerque, NM 87131, (3) Geosciences Research Div, Scripps Inst. of Oceanography, La Jolla, CA 92037, (4) Earth and Planetary Sciences, Univ of New Mexico, 200 Yale Blvd NE, Northrop Hall, Albuquerque, NM 87131, (5) Biology, University of New Mexico, Castetter Hall, Albuquerque, NM 87131, (6) Biology, University of New Mexico, Albuquerque, NM 87131

We report geochemical and microbial results from a suite of hot and cold springs, and CO2 geysers in traverses across the Aspen anomaly.  The Aspen anomaly is a low-velocity mantle domain coinciding with the intersection of the Rio Grande rift and the Colorado Mineral belt.  Quaternary travertine and active CO2-rich springs in the study region reflect a long-lived interaction of neotectonics, deeply-sourced (endogenic) fluids and the surficial hydrologic regime.  He isotope and water chemistry data show mixing between surface water recharge and inputs from deep crustal and mantle sources. Endogenic components have high 3He/4He, high CO2, and high salinity compared to recharge waters; they also exhibit elevated trace element concentrations (e.g., F, Li, As, U). Spatial correlation of helium isotope data with mantle velocity structure determined from tomographic studies suggest heterogeneous mantle degassing, with highest 3He/4He in surface waters (hence highest mantle helium contribution) corresponding to regions of lowest mantle velocity. Gas compositions are dominated by CO2 (up to 99 %).  Aqueous geochemical modeling indicates that considerable external carbon is present (up to 0.02 mol/L; external carbon = HCO3-(Ca+Mg) with an adjustment for possible gypsum contribution to the calcium term). Hydrogen and reduced sulfur are present, as well as elevated He (low N2/He) and helium isotope values as high as 2.17 RA (RA= air 3He/4He) indicating a mantle input. CO2/3He ranges from 107 to 1012, and d13C values range from -2 to -10‰. These springs represent a flux of deeply-sourced carbon to the atmosphere (at 1800 l/s, Glenwood Springs emits 109 mol C/yr). High CO2 abundance, hydrogen, and a suite of redox-sensitive trace components offer a chemically-rich setting for a diverse microbial community. These systems are geochemically analogous to the chemolithotrophic microbial ecosystems associated with mid-ocean ridges (hence “continental smokers”).  Analysis of microbial community small sub-unit ribosomal RNA genes by DNA sequencing is underway to test for differences among the sites and the presence of microorganisms utilizing similar metabolic pathways to those found in oceanic hydrothermal settings.

2006 Philadelphia Annual Meeting (22–25 October 2006)
General Information for this Meeting
Session No. 192
Geochemical and Hydrologic Linkages Between Shallow and Deep Groundwaters
Pennsylvania Convention Center: 104 A
8:00 AM-12:00 PM, Wednesday, 25 October 2006

Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 465

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