HR: 17:00h
AN: V44A-05    [Abstracts]
TI: Geochemistry of Hydrothermal Fluids in South Mariana Backarc Spreading Center
AU: * Ishibashi, J
EM: ishi@geo.kyushu-u.ac.jp
AF: Faculty of Science, Kyushu Univ., 6-10-1 Hakozaki Higashi-ku, Fukuoka, 812-8581 Japan
AU: Yamanaka, T
EM: tyama@rc.kyushu-u.ac.jp
AF: School of Social & Cultural Studies, Kyushu Univ., 4-2-1 Ropponmatsu Chuo-ku, Fukuoka, 810-8560 Japan
AU: Kimura, H
EM: shkimur@ipc.shizuoka.ac.jp
AF: Inst. Biological Research & Function, AIST, 1-1-1 Higashi, Tsukuba, 305-8566 Japan
AU: Hirota, A
EM: hirota-akinari@aist.go.jp
AF: School of Science, Hokkaido Univ., N10W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Toki, T
EM: toki@ori.u-tokyo.ac.jp
AF: School of Science, Hokkaido Univ., N10W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Tsunogai, U
EM: urumu@ep.sci.hokudai.ac.jp
AF: School of Science, Hokkaido Univ., N10W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Gamo, T
EM: gamo@ori.u-tokyo.ac.jp
AF: School of Science, Hokkaido Univ., N10W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Utsumi, M
EM: utsumi@bsys.tsukuba.ac.jp
AF: School of Life & Environmental Sciences, Tsukuba Univ., 1-1-1 Tennodai, Tsukuba, 305-8577 Japan
AU: Roe, K
EM: kevin.roe@.noaa.gov
AF: NOAA, Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Miyabe, S
EM: miyabe@misasa.okayama-u.ac.jp
AF: Inst. Study of Earth's Interior, Okayama Univ., 827 Yamada, Misasa, 682-0193 Japan
AU: Okamura, K
EM: okamurak@scl.kyoto-u.ac.jp
AF: Inst. Chemical Research, Kyoto Univ., Gokasho, Uji, 611-0011 Japan
AB: Fluid samples were collected from active hydrothermal sites along the south Mariana backarc spreading center, during dive programs with SHINKAI6500 (JAMSTEC) / {\it Yokosuka} (YK03-09 cruise) in Oct. 2003, and with ROPOS (CSSF) / {\it Thomas G. Thompson} (TN167A cruise) in March 2004. Fluid geochemistry shows diversity among three sites, probably reflecting their geological settings. High temperature fluid (T=$315\deg$C) from black smokers at the top of an off-axis seamount (Pika site: 12$\deg$55.1'N, 143$\deg$38.9'E, depth=2830m) shows metal-rich signature and high Cl concentration (=600mM). Modest high temperature fluid (T=$213\deg$C) from giant sulfide structure of a few ten meters high (Archaean Site: 12$\deg$56.3'N, 143$\deg$38.0'E, depth=2990m) shows slight K-rich from ridge-type fluids and low Cl concentration (=470mM). On the other hand, along the spreading axis, only shimmering venting directly from basaltic seafloor was observed (Fryer site: 12$\deg$57.2'N, 143$\deg$37.2'E, depth=2880m). Although temperature of the venting fluid were reported as $240\deg$C when this site was discovered at May 2003, it has decreased to $110\deg$C at Oct. 2003, and to $70\deg$C at March 2004. Based on fluid chemistry composition, the shimmering fluid is considered as formed by mixing between hydrothermal fluid endmember (Mg=0) with seawater, and hydrothermal contribution has diminished for this one year. We also successfully collected fluid samples venting from the casing pipes which had been drilled by BMS at January 2004. The fluid (T=$30\deg$C) from APM01 located in the vicinity of Fryer site showed chemistry well explained by mixing of the same hydrothermal fluid endmember with seawater. Under the framework of Achaean Park Project, samples for microbiological studies were collected simultaneously, and these geochemical data provides basic information for them.
DE: 8424 Hydrothermal systems (8135)
DE: 9355 Pacific Ocean
DE: 4832 Hydrothermal systems
DE: 1050 Marine geochemistry (4835, 4850)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting