HR: 0800h
AN: V21D-0756    [Abstracts]
TI: Acive shallow-water submarine hydrothermal venting and occurence of chimney-like mineral deposits from Northern Kagoshima Bay, South Kyushu, Japan
AU: * Yamanaka, T
EM: toshiroy@cc.okayama-u.ac.jp
AF: Okayama University, 1-1, Naka 3-chome, Tsushima, Okayama, 700-8530, Japan
AU: Ishibashi, J
EM: ishi@geo.kyushu-u.ac.jp
AF: Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
AU: Maeto, K
EM: sc16528@cc.okayama-u.ac.jp
AF: Okayama University, 1-1, Naka 3-chome, Tsushima, Okayama, 700-8530, Japan
AU: Nakaseama, M
EM: 81-92-642-2684
AF: Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
AU: Okamura, K
EM: okamurak@cc.kochi-u.ac.jp
AF: Kochi University, B200 Monobe, Nankoku, Kochi, 783-8502, Japan
AU: Sugiyama, T
EM: b043h043m?�\s.kochi-u.ac.jp
AF: Kochi University, B200 Monobe, Nankoku, Kochi, 783-8502, Japan
AU: Fujino, K
EM: yamaikei@mine.kyushu-u.ac.jp
AF: Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
AU: Kimura, H
EM: shkimur@ipc.shizuoka.ac.jp
AF: Kochi University, B200 Monobe, Nankoku, Kochi, 783-8502, Japan
AU: Kimura, H
EM: shkimur@ipc.shizuoka.ac.jp
AF: Shizuoka University, 836 Otani, Suruga-ku, Shizuoka, 422-8529, Japan
AU: Chiba, H
EM: hchiba@cc.okayama-u.ac.jp
AF: Okayama University, 1-1, Naka 3-chome, Tsushima, Okayama, 700-8530, Japan
AB: At least three active volcanoes are located in and around Kagoshima Bay, South Kyushu, Japan. The bay has been considered a tectonic graben formed under extensional stress associated with subduction of the Philippine-sea plate sinking below the Eurasia plate and the axis of graben is extended along the volcanic front. In addition, the bay head area is a part of the Aira caldera, it is considered to form ca. 25,000 yeas ago. The Wakamiko crate (31°40'N, 130°46'E) is an active crater of the caldera and the depression of crater is buried by a thick (up to 80m) unconsolidate deposits. Therefore, the crater floor shows quite flat feature and the depth of floor is ca. 200m. In the crater hydrothermal activity has been recognized, however, active vent of hydrothermal fluid is not found except two gentle shimmering from fissure and small collapse developed on muddy floor. During the dive study of ROV/Hyper-Dolphin of JAMSTEC (R/V Natsushima, NT07-09 Cruise) in June 2007, active hydrothermal venting (T > 186°C) was found on the crater floor, and the venting as ca. 10- cm-wide jet of hot water without gas was observed atop of mineralized chimney-like structure up to 1.5 m in height. The chimney was composed mainly native sulfur, sulfate minerals, silica, and small amount of sulfides such as pyrite, stibnite, realgar and cinnabar. Chemistry of the venting fluid was almost comparable with one of the shimmering fluids obtained as pore water, which was characterized by low salinity (Cl = 300mM) and higher K concentration than seawater. Analyses of detailed chemistry and mineralogy of the fluid and chimney is under way.
DE: 3015 Heat flow (benthic)
DE: 3075 Submarine tectonics and volcanism
DE: 3665 Mineral occurrences and deposits
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting