HR: 17:15h
AN: V34B-06    [Abstracts]
TI: Vapor-rich Hydrothermal Fluid Migration Within Pumiceous Sediment in the Iheya North Knoll, Okinawa Trough
AU: * Ishibashi, J
EM: ishi@geo.kyushu-u.ac.jp
AF: Dept. Earth Planet. Sci., Faculty Science, Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 8128581, Japan
AU: Suzuki, R
EM: rsuzu@geo.kyushu-u.ac.jp
AF: Dept. Earth Planet. Sci., Faculty Science, Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 8128581, Japan
AU: Hamasaki, H
EM: hamasaki@geo.kyushu-u.ac.jp
AF: Dept. Earth Planet. Sci., Faculty Science, Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 8128581, Japan
AU: Yamanaka, T
EM: toshiroy@cc.okayama-u.ac.jp
AF: Faculty Science, Okayama Univ., 3-1-1 Tsushima-naka, Okayama, 7008530, Japan
AU: Chiba, H
EM: hchiba@cc.okayama-u.ac.jp
AF: Faculty Science, Okayama Univ., 3-1-1 Tsushima-naka, Okayama, 7008530, Japan
AU: Tsunogai, U
EM: urumu@ep.sci.hokudai.ac.jp
AF: Faculty Science, Hokkaido Univ., N10W6, Sapporo, 0600810, Japan
AU: Ijiri, A
EM: ijiri@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima, Yokosuka, 2370061, Japan
AU: Nakagawa, S
EM: nakagawas@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima, Yokosuka, 2370061, Japan
AU: Nunoura, T
EM: takuron@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima, Yokosuka, 2370061, Japan
AU: Takai, K
EM: kent@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima, Yokosuka, 2370061, Japan
AU: Kinoshita, M
EM: masa@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima, Yokosuka, 2370061, Japan
AU: Ashi, J
EM: ashi@ori.u-tokyo.ac.jp
AF: Ocean Res. Inst., Univ. Tokyo, 1-15-1 Minami-dai Nakano-ku, Tokyo, 1648639, Japan
AB: The newly developed ROV NSS (Navigable Sampling System) enabled pin-point piston core sampling from the active hydrothermal field. In the Iheya North hydrothermal field in the mid-Okinawa Trough (27°47.5'N, 126°53.8'E, depth = 1000m), animal colonies are observed not only around the central mound structure (named as NBC) which discharges vigrously high temperature (T=311°C) clear fluid, but also as Calyptogena colony at 200m east from the NBC mound and as tube-worm colony at 250m southeast from the NBC mound. During Leg 3 of KY05-14 cruise (R/V Kaiyo of JAMSTEC) in Jan. 2005, fourn piston cores were successfully recovered with length from 65cm to 250cm. Surface sediments from the Calyptogena colony and the tube-worm colony were revealed as mainly composed of pumiceous sediment. Pore fluids from the Calyptogena Field showed unusual chemistry characterized as very low salinity (Cl=420mM), low Mg concentration, significantly lower Na/Cl ratio than seawater and high methane concentration, which suggests contribution of a vapor-rich hydrothermal component migrating within the pumice layer from the activity center. Moreover, decrease of SO₄ accompanied by increase of alkalinity is notable even less than one meter depth below the seafloor. In situ sulfate reduction in the surface sediment caused by entrainment of the hydrothermal component would be a source of hydrogen sulfide that supports Calyptogena colony.
DE: 3004 Gas and hydrate systems
DE: 3021 Marine hydrogeology
DE: 4825 Geochemistry
DE: 8404 Volcanoclastic deposits
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting