HR: 0800h
AN: T31A-0479    [Abstracts]
TI: Vent Fluid Chemistry From Six Hydrothermal Fields Along the Eastern Lau Spreading Center From 20°03'S to 22°13'S.
AU: * Sharkey, J
EM: jessica_sharkey@csumb.edu
AF: Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA 95039
AU: Wheat, C G
EM: wheat@mbari.org
AF: Univeristy of Alaska Fairbanks, PO Box 757220 , Fairbanks, AK 99775
AU: Mottl, M J
EM: mmottl@soest.hawaii.edu
AF: University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822
AU: Seewald, J
EM: jseewald@whoi.edu
AF: Woods Hole Oceanographic Institute, WHOI MS#4, Woods Hole, MA 02543
AB: As part of a series of R2K and NSF funded explorations of the Eastern Lau Spreading Center, we participated in a cruise between April and May of 2005 aboard the R/V Melville. Eighty-one fluid samples were collected from six hydrothermal fields that span from 20°03'S to 22°13'S (from north to south: Kilo Moana, TowCam, Abe, Tui Malia, Mariner, and Vai Lili) using the ROV Jason 2. Fluids samples were collected using both isobaric gas-tight and major samplers from focused and diffuse vents to determine vent fluid composition and establish the hydrogeologic and geochemical processes occurring at depth. We report here on dissolved ion concentrations from vent fluids. The maximum vent temperature and magnesium concentration from individual orifices ranged from 11 to 363 ° C and from 51.7 to 0.65mmol/kg, respectively. The Mariner site had the lowest pH of 2.5 and the greatest H2S concentration of approximately 9mmol/kg. All samples had alkalinities less than seawater. Chlorinities were both depleted and enriched relative to seawater (around 538 mmol/kg), ranging from 530 to 650mmol/kg. Fe endmember concentration is about 12mmol/kg at Mariner and 3mmol/kg at Kilo Moana, but less than 0.3mmol/kg for the other sites. Fe/Mn molar ratios range from 4.7 at Kilo Moana to 0.1 at Vai Lili. Systematic along strike variations were observed in the endmember abundance of some aqueous species. For example, values for Si and Li are greater to the north whereas concentrations of K are greater to the south. Compilations of endmember compositions for individual orifices and fields are being compiled for all major, minor and certain trace ions in seawater. Trends will be incorporated with geological and biological data to elucidate hydrothermal processes along this geologically diverse transect. We are particularly interested in assessing the response of fluid chemistry to variations in the composition and structure of the crust resulting from the increase influence of subduction related processes to the south.
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