HR: 0800h
AN: V51C-1490    [Abstracts]
TI: First Submersible Dives on Brothers Volcano, Kermadec Arc, Offshore New Zealand
AU: * de Ronde, C E
EM: cornel.deronde@gns.cri.nz
AF: GNS, PO Box 31-312, Lower Hutt, 6135 New Zealand
AU: Massoth, G J
EM: g.massoth@gns.cri.nz
AF: GNS, PO Box 31-312, Lower Hutt, 6135 New Zealand
AU: Ishibashi, J
EM: ishi@geo.kyushu-u.ac.jp
AF: Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581 Japan
AU: Embley, R W
EM: robert.w.embley@noaa.gov
AF: NOAA/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AU: Lupton, J E
EM: lupton@pmel.noaa.gov
AF: NOAA/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AU: Butterfield, D A
EM: david.a.butterfield@noaa.gov
AF: NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Yamanaka, T
EM: tyama@rc.kyushu-u.ac.jp
AF: Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581 Japan
AU: Evans, L J
EM: evans@pmel.noaa.gov
AF: NOAA/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AU: Takai, K
EM: kent@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AB: Previous NZAPLUME and other cruises between 1999 and 2004 established that at least three major hydrothermal sites occur at Brothers; the NW caldera and cone sites are actively venting while the SE caldera site is extinct. In October 2004, the submersible Shinkai 6500 did 4 dives on Brothers as part of the SWEEP Vents expedition, the first dives anywhere along the 2,500 Kermadec-Tonga arc. Between April and May, 2005, an additional 5 dives were made at Brothers using the HURL submersible Pisces V as part of a New Zealand and NOAA co-sponsored expedition. In total, 6 dives have been done at the NW caldera site and 3 at the cone site. The NW caldera site is host to a significant sulfide deposit. It mainly crops out along a zone of discrete, narrow, fault bounded ledges between ~1600 and 1680 m, over strike lengths up to ~500 m. Locally, bands of active and extinct black smoker chimneys up to 7 m tall occur in this zone and strike orthogonal to the caldera walls, indicative of cross structures. Abundant sulfide talus and subcropping massive sulfides also occur at this site. The submersible dives recorded extensive alteration of the caldera walls and sampled individual chimneys, Fe-oxide crusts, and altered rocks. The cone site is hosted by ash and talus and is dominated near its summit by extensive deposition of elemental S and Fe-oxide crusts. No sulfides have been recovered from this site. Preliminary vent fluids results are from samples collected by the Shinkai 6500. They show two very different hydrothermal fluids. Those from the NW caldera site have temperatures up to 302°C, pH down to 2.8, low Mg and SO₄ values, Cl between 510 and 760 mM, elevated Si and increasing Fe and Mn values with increasing Cl concentrations, consistent with a Cl-enriched endmember. By contrast, vent fluids from the cone site are gas-rich (up to 220 mM total gas), have temperatures <70°C, pH down to 1.9, Mg values near seawater concentrations and higher, Cl <550 mM and low levels of Si, Fe and Mn, consistent with a vapor-dominated phase. Water δD values for both sites are <0 per mil. Together, these results suggest subseafloor phase separation with the NW caldera site a chronic system dominated by evolved seawater and the cone site a nascent magmatic-hydrothermal system.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 3665 Mineral occurrences and deposits
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005