HR: 1340h
AN: V43D-1440    [Abstracts]
TI: Multi-Sensor Mapping of Diffuse Degassing of C-O-H Compounds in Terrestrial Hydrothermal Systems
AU: * Schwandner, F M
EM: fschwandner@asu.edu
AF: Arizona State University, Dept. Geological Sciences, P.O. Box 871404, Tempe, AZ 85287-1404 United States
AU: Shock, E L
EM: eshock@asu.edu
AF: Arizona State University, Dept. Geological Sciences, P.O. Box 871404, Tempe, AZ 85287-1404 United States
AB: In-situ single-sensor detection and mapping of diffuse degassing phenomena in hydrothermal and volcanic areas can be used to elucidate subsurface tectonic structures, assess emission rates, and to monitor emission variability (Williams 1985; Chiodini et al. 1996, Werner et al., 2003). More than one technique has been deployed to measure several gas species simultaneously (e.g., Crenshaw et al. 1982), and correlations of one gas species (usually CO$_{2}$) with physical parameters like heat flux (Brombach et al., 2001), or with one other gas species (Rn, He) have been demonstrated (Barberi & Carapezza 1994; Williams-Jones et al., 2000). Recently, correlations of multiple gas species with one another were reported (Schwandner et al., 2004), leading to the possibility of quantitative mapping of subsurface hydrothermal chemical processes by simultaneous measurement of reaction partners and products that continuously and diffusely degas. In the present study, we joined a fully-quantitative multi-sensor instrument (Draeger Multiwarn II) to a modified accumulation-chamber sensing method (Chiodini et al., 1996) and measured diffuse degassing of CH$_{4}$, H$_{2}$, CO$_{2}$, CO, and H$_{2}$S. In this approach, each batch of gas that is recirculated through the detector is simultaneously analyzed by all sensors. To test this approach we chose two magmatically influenced, hydrothermally active areas at Yellowstone National Park (USA): Sylvan Springs and the Greater Obsidian Pool Area. The area near Obsidian Pool was previously studied during a diffuse CO$_{2}$ degassing campaign (Werner & Brantley, 2004). Preliminary results show that elevated reduced gas emissions appear to be most prominent near hydrothermal pools, whereas CO$_{2}$-dominated degassing anomalies highlight subsurface tectonic structures. This multimodal distribution allows us to distinguish deep degassing sources (CO$_{2}$ anomalies) from shallow localized hydrothermal processes (reduced gas anomalies). The results permit us to positively identify and partially map a previously-inferred active lineament in the Obsidian Pool area. In addition, reduced gas data are yielding areal ratio distributions of CO/CO$_{2}$, H$_{2}$/CH$_{4}$, and CO/CH$_{4}$, that may be indicative of reactions such as the catalytic hydrogenation of CO$_{2}$ (Sabatier-Process) and of CO (Fischer-Tropsch-Process) within the shallow hydrothermal system. Barberi & Carapezza (1994). Bull. Volcanol. 56(5): 335-342. Brombach, et al. (2001). Geophys. Res. Lett. 28(1): 69-72. Crenshaw et al. (1982). Nature 300: 345-346. Chiodini et al. (1996). Bull. Volcanol. 58(1): 41-50. Schwandner et al. (2004). JGR D 109: D04301, doi:10.1029/2003JD003890. Werner & Brantley (2004) JGR B 105: 10,831-10,846. Werner et al. (2003). Earth Planet. Sci. Lett. 210: 561-577. Williams (1985). Science 229(4713): 551-553. Williams-Jones et al. (2000). Bull. Volcanol. 62: 130-142.
UR: http://geopig.asu.edu
DE: 8424 Hydrothermal systems (8135)
DE: 8494 Instruments and techniques
DE: 1094 Instruments and techniques
DE: 0400 Biogeosciences
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting