HR: 17:45h
AN: V54A-08    [Abstracts]
TI: A Systematic Reconnaissance of Submarine Hydrothermal Venting Along the South Tonga (Tofua) Intra-oceanic arc
AU: * Massoth, G J
EM: g.massoth@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, 30 Gracefield Road, Lower Hutt, 6009 New Zealand
AU: Baker, E T
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-6319 United States
AU: Lupton, J E
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 2115 Marine Science Drive, Newport, OR 97365-5258 United States
AU: de Ronde, C E
AF: Institute of Geological and Nuclear Sciences, 30 Gracefield Road, Lower Hutt, 6009 New Zealand
AU: Walker, S L
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-6319 United States
AU: Ishibashi, J
AF: Kyushu University, Faculty of Science, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 000000 Japan
AU: Worthington, T J
AF: University of Kiel, Olshausenstr. 40, Kiel, D-24118 Germany
AU: Arculus, R J
AF: Australian National University, Department of Geology, Canberra, ACT 0200 Australia
AU: Resing, J A
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-6319 United States
AU: Greene, R R
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 2115 Marine Science Drive, Newport, OR 97365-5258 United States
AU: Lebon, G T
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-6319 United States
AU: Nakamura, K
AF: National Institute of Advanced Industrial Sciene and Technology, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki Japan
AU: Stoffers, P
AF: University of Kiel, Olshausenstr. 40, Kiel, D-24118 Germany
AB: The Tonga-Eastern Lau Vents Expedition (TELVE) of March-April 2003 provided the first survey of hydrothermal plumes along 425 km of the south Tonga (Tofua) arc, between $\sim$$21\deg$S and $25\deg$S. The volcanic front in this arc section lies $\sim$180 km west of the deepest point in the southern hemisphere (Horizon Deep in the Tonga Trench), $\sim$55 km west of the Tonga ridge, and $\sim$40 km east at closest approach to the Valu Fa and Eastern Lau back-arc spreading complex. Twenty-four of the 25 volcanic centers that comprise this arc section are submarine. We used conventional hydrothermal plume reconnaissance protocols (towed CTDO-Eh sensors + discrete water sampling for helium abundance and isotopic ratios, methane, pH, hydrogen sulphide, and total dissolvable Mn and Fe) to systematically survey 19 submarine volcanoes of the south Tonga arc for magmatic-hydrothermal fluid emissions. We found about one-third of the volcanoes (seven) to be hydrothermally active, with four venting at dual, spatially discrete sites and depths, for a total of eleven venting sites. While the deepest plume was sampled at $\sim$1400 m depth, plumes at nine sites were $<$1000 m deep and at six sites $<$500 m deep. This site frequency for venting is intermediate to that found during recent surveys along other Western Pacific intra-oceanic arcs (Kermadec higher, Mariana lower) and the relatively shallow depth regime for discharge, compared to most MOR venting sites, is similar. The compositions of the south Tonga arc plumes were chemically diverse: Fe/Mn varied from $<$1 to $>$50, total dissolved Fe concentrations ranged from $<$10 nM to $>$300 nM, only one site provided a large negative anomaly in pH (an indicator for ultra-high volatile content), and the presence of hydrogen sulphide was never detected, contrary to our experience at other submarine arcs. While high $\delta$$^{3}$He values were observed (74% maximum), sources located deeper than the arc sites appear to be volumetrically more important to the regional depth distribution of $^{3}$He. We place these results within the contexts of regional and global submarine hydrothermal emissions to assess their significance.
DE: 8424 Hydrothermal systems (8135)
DE: 8135 Hydrothermal systems (8424)
DE: 4825 Geochemistry
DE: 3035 Midocean ridge processes
DE: 1050 Marine geochemistry (4835, 4850)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting