HR: 0800h
AN: V41B-1381    [Abstracts]
TI: Geochemical studies on the biodiversity and hydrothermal activity; mineralogy, chemistry, and age determination of hydrothermal chimney collected from Suiyo seamount, Izu-Bonin arc
AU: * Noguchi, T
EM: k048570@sci.u-ryukyu.ac.jp
AF: Graduate school of Engineering and Science, Univ. of the Ryukyus, Senbaru 1, Nishihara, Okiwana, 903-0213 Japan
AU: Oomori, T
EM: oomori@sci.u-ryukyu.ac.jp
AF: Faculty of Science, Univ. of the Ryukyu, Senbaru 1, Nishihara, Okinawa, 903-0213 Japan
AU: Taira, N
EM: k032316@eve.u-ryukyu.ac.jp
AF: Graduate school of Engineering and Science, Univ. of the Ryukyus, Senbaru 1, Nishihara, Okiwana, 903-0213 Japan
AU: Takada, J
EM: takada@HL.rri.kyoto-u.ac.jp
AF: Kyoto University Research Reactor Institute, Kumatori-cho Sennan-gun, Osaka, 590-0494 Japan
AU: Urabe, T
EM: urabe@eps.s.u-tokyo.ac.jp
AF: Dept. of Earth & Planetary_@Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AB: Hydrothermal chimney structure has the steep environmental gradients of temperature, redox potential, pH and chemical concentration, which will provide diverse microhabitats for microbial communities (K.Takai et al. 2001, Hermie J.M. Harmsen et al. 1997). It is important for detailed understanding of the biodiversity to determine the chimney structural environment. Suiyo seamount is located $28.57\deg$N, $140.66\deg$E, where is suitable to compare with the Mid-ocean ridge hydrothermal field, because of few influence of terrestrial sediment. It was reported that the magma chamber below the seamount was very shallow ($\sim$1 km), and high temperature hydrothermal fluid chamber was underlying just below the seafloor sealed with anhydrite and barite. Chimney samples used in this study were collected by Dive 1222-1225 of SHINKAI 2000 (JAMSTEC) in 2000. We measured the chemical composition with neutron activation analysis (NAA) and X-ray fluorescence analysis (XRF), mineral composition with X-ray diffraction analysis (XRD), and the precipitation age measurements ($\sim$200 years) of these chimneys with $\gamma$-ray spectrometry ($^{210}$Pb/Pb method, $^{228}$Th/$^{228}$Ra method, and $^{210}$Pb/$^{226}$Ra method). The mineral composition of the Suiyo seamount chimney were contained barite (BaSO$_{4}$), sphalerite ((Zn,Fe)S), pyrite (FeS$_{2}$), and chalcopyrite (CuFeS$_{2}$) as a major mineral constituents. The chemical composition shows that gold contents in the chimney collected from Suiyo seamount were much higher (maximum 166 ppm) than other hydrothermal field. The chronological study showed that the precipitation ages of sulfide chimney samples (ranged in 37.2-79.6 years before 2002 by $^{210}$Pb/Pb method) were older than barite chimney ((ranged in 2.9-8.2 years before 2002 by $^{228}$Th/$^{228}$Ra method). We will discuss about the process of chimney formation, the temporal variation of the past hydrothermal activity and the difference from other submarine hydrothermal fields (EPR, MAR, Okinawa trough, Loihi seamount).
DE: 8424 Hydrothermal systems (8135)
DE: 4832 Hydrothermal systems
DE: 4803 Bacteria
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting