HR: 0800h
AN: T31A-0478    [Abstracts]
TI: Aqueous Volatiles in Lau Basin Hydrothermal Fluids
AU: * Seewald, J
EM: jseewald@whoi.edu
AF: Dept. of Marine Chemistry and Geochemistry, WHOI, Woods Hole, MA 02543 United States
AU: McCollom, T
EM: mccollom@lasp.colorado.edu
AF: LASP, University of Colorado, Boulder, CO 80309 United States
AU: Proskurowski, G
EM: giora@whoi.edu
AF: Dept. of Marine Chemistry and Geochemistry, WHOI, Woods Hole, MA 02543 United States
AU: Reeves, E
EM: ereeves@whoi.edu
AF: Dept. of Marine Chemistry and Geochemistry, WHOI, Woods Hole, MA 02543 United States
AU: Mottl, M
EM: mmottl@soest.hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, HI 96826 United States
AU: Sharkey, J
EM: jessica_sharkey@csumb.edu
AF: MLML, MLML, Moss Landing, CA 95039 United States
AU: Wheat, C G
EM: wheat@mbari.org
AF: GURU, University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Tivey, M
EM: mktivey@whoi.edu
AF: Dept. of Marine Chemistry and Geochemistry, WHOI, Woods Hole, MA 02543 United States
AB: The Lau Basin is a back-arc spreading center characterized by widespread hydrothermal activity. High and low temperature vent fluids were collected from six vent fields along the Eastern Lau Spreading Center (ELSC) and the Valu Fa Ridge (VFR) using isobaric gas-tight samplers during R/V Melville cruise TUIM05MV. Fluids were analyzed for the abundances of H₂, H₂S, CH₄, CO₂, and CO to assess chemical environments inhabited by biological vent communities and constrain fluid-rock reactions and magmatic processes in subsurface environments. Maximum measured temperatures for focused venting in these areas varied from 309 to 363°C. Water depths decreased from ~2700m for sites sampled at the northern end of the ELSC to ~1725m for the southern most site sampled on the VFR. Endmember concentrations of dissolved H₂ at the Kilo Moana, TowCam, and ABE vent fields on the ELSC varied from 0.054 to 0.498 mmol/l and showed a systematic interfield decrease from north to south along the ridge crest. A similar spatial trend was observed for endmember H₂S concentrations that varied from 2.6 to 6.6 mmol/l. In contrast to H₂ and H₂S, aqueous CH₄ abundances that varied from 0.028 to 0.057 mmol/l increased from north to south. In general, fluids from the Tui Malila, Mariner, and Vai Lili vent fields on the VFR showed greater compositional variability than fluids venting along the ELSC and an absence of systematic along strike chemical trends. Endmember H₂, H₂S, and CH₄ abundances at VFR ranged from 0.0029 to 0.178 mmol/l, 0.010 to 9.6 mmol/l, and 0.0029 to 0.043 mmol/l, respectively. Endmember concentrations of dissolved CO at ELSC and VFR varied from 0.01 to 0.1 umol/l and showed systematic variations with dissolved H₂ and CO₂ abundances. Assessment of the CO, CO₂, and H₂ concentrations within a thermodynamic framework suggests that these species have attained equilibrium states at measured vent temperatures and pressures. The higher degree of compositional variability observed in vents fluids from VFR likely reflects the occurrence of three distinct styles of hydrothermal activity along this portion of the ridge-crest. While the Tui Malila field appears most similar to vent fields along the ELSC with fault-related hydrothermal activity, higher temperatures and abundances of magmatic CO₂ at Mariner point to a significant role for ongoing magmatic processes in regulating vent fluid chemistry. In contrast, absence of focused flow, maximum temperatures of 121°C, and low volatile abundances at Vai Lili suggests that this location may be in the waning stages of hydrothermal activity.
DE: 1020 Composition of the continental crust
DE: 3015 Heat flow (benthic)
DE: 3035 Midocean ridge processes
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
DE: 7218 Lithosphere (1236)
SC: Tectonophysics [T]
MN: Fall Meeting 2005