HR: 16:45h
AN: V34B-04    [Abstracts]
TI: Volatile Chemistry at Lau Basin Hydrothermal Sites: Basin-Wide Trends of Slab Carbonate Influence and Suggestions of Abiotic Methane Oxidation at the Mariner Vent Site
AU: * Proskurowski, G
EM: giora@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd, Woods Hole, MA 02543, United States
AU: Seewald, J S
EM: jseewlad@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd, Woods Hole, MA 02543, United States
AU: Reeves, E
EM: ereeves@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd, Woods Hole, MA 02543, United States
AU: McCollom, T M
AF: LASP- University of Colorado, Boulder, 1234 Innovation Drive, Boulder, CO 80309, United States
AU: Lupton, J
EM: John.E.Lupton@noaa.gov
AF: NOAA/PMEL, 2115 Marine Science Drive, Newport, OR 97365, United States
AU: Sylva, S
EM: ssylva@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd, Woods Hole, MA 02543, United States
AU: Tivey, M K
EM: mktivey@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd, Woods Hole, MA 02543, United States
AB: The Lau Basin is actively spreading along three major spreading centers: the Central Lau Spreading Center (CLSC) in the north, the Eastern Lau Spreading Center (ELSC), and the Valu Fa Ridge (VFR) to the south. A southward progression along these spreading centers reveals decreasing spreading rates, decreasing distance to the arc, and a corresponding increase in the influence of the subducted Pacific plate slab (1, 2). Analysis of the d13CO2 and He data from volatile samples collected during a 2005 expedition to six hydrothermal sites along the ELSC and VFR reveals a systematic and continuous relationship between latitude (distance from the arc) and the arc-derived component of the signal. This smooth and linear transition from arc-like hydrothermal volatiles in the south to more MORB-like hydrothermal volatiles in the north contrasts the interpretation from the dredged geologic record that suggests an extremely sharp andesite-basalt transition occurring along the southern portion of the ESLC (3). The Mariner vent site, the southernmost high-temperature site visited in 2005, exhibits an arc-influenced volatile chemistry that is different from the other Lau Basin sites. The ESLC and northern VFR vents are characterized by CO2 concentrations ranging from 1-12 mmol/kg while the Mariner site has higher CO2 values, up to 60 mmol/kg. The opposite trend is seen in the methane concentrations as the northern vents range from 25-55 μmol/kg while Mariner methane values are much lower, at 5-7 μmol/kg. Isotopic results also illustrate the unique chemistry of the Mariner site: d13CO2 values are in the typical MOR-hydrothermal range of -7 to -4 per mil at northern vents and near 0 per mil at Mariner, and d13CH4 values are in the typical MOR-hydrothermal range of - 25 to -20 per mil at northern vents, and highly enriched, -7 to +0.7 per mil at Mariner. The CO2/3He ratio and the d13CO2 values at Mariner suggest that 80 percent of the CO2 at Mariner is sourced from carbonates, presumably from authigenically formed carbonates in the downgoing slab. The low CH4 concentrations and uniquely enriched d13CH4 signatures at Mariner are hypothesized to be the result of abiotic methane oxidation at hydrothermal temperatures. 1. Jacobs, A.M., A. J. Harding, G. M. Kent, Earth and Planetary Science Letters 259, 239 (2007). 2. Martinez, F., B. Taylor, E. T. Baker, J. A. Resing, S. L. Walker, Earth and Planetary Science Letters 245, 655 (2006). 3. Bezos, A., et al., Eos, Transactions, American Geophysical Union 86, Abstract V41C (2005).
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting