HR: 0800h
AN: V51C-1494    [Abstracts]
TI: Submarine Volcanoes and High-Temperature Hydrothermal Venting on the Tonga Arc, SW Pacific
AU: Stoffers, P
EM: pst@gpi.uni-kiel.de
AF: Institut fuer Geowissenschaften, Universitaet Kiel, Olshausenstr. 40, Kiel, 24098 Germany
AU: Worthington, T J
EM: tw@gpi.uni-kiel.de
AF: Institut fuer Geowissenschaften, Universitaet Kiel, Olshausenstr. 40, Kiel, 24098 Germany
AU: Hannington, M D
EM: mhanning@uottawa.ca
AF: Dept. of Earth Sciences, University of Ottawa, Ottawa, K1N 6N5 Canada
AU: Schwarz-Schampera, U
EM: u.schwarz-schampera@bgr.de
AF: Bundesanstalt fuer Geowissenschaften und Rohstoffe, Stilleweg 2, Hannover, 30655 Germany
AU: * Massoth, G J
EM: g.massoth@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, 69 Gracefield Rd, PO Box 30368, Lower Hutt, 6007 New Zealand
AU: Lundsten, L J
EM: lonny@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Rd, Moss Landing, CA 95039 United States
AB: The first submarine hydrothermal vents and associated seafloor mineralization on the Tonga arc have been found in the summit calderas of two shallow-water volcanoes, greatly extending the known areas and diversity of seafloor hydrothermal activity in the western Pacific region. The highest temperature vents (245-265 °C) occur at water depths of 385-540 m near the summit of a large volcano at 24°S. They comprise clusters of large (to 10 m high) barite, anhydrite, and sulfide chimneys surrounded by extensive deposits of Fe-oxyhydroxides. The chimneys are characterized by vigorous venting of clear fluids with temperatures on the seawater boiling curve. There is abundant evidence of phase separation, which can be seen as flame-like jets of steam (H₂O vapor) discharging from the chimney orifices. Pyrite, marcasite, sphalerite, and chalcopyrite line the interiors of the highest temperature vents, similar to black smoker chimneys on the mid-ocean ridges. A second, spatially distinct, vent field occurs at water depths of 850-985 m within a large caldera on the western side of the volcano. Venting is more diffuse and at lower temperature in this field (to 112 °C), which features large clusters of Fe-oxyhydroxide and silica chimneys at its core. Both vent fields are spatially related to basaltic dike swarms. Low-temperature venting (to 152 °C) was also found on a second volcano at 21°S. There, venting occurs at the southern end of a chain of youthful explosion craters, and is most intense in water-depths of 160-210 m. Large fields of mussels and white filamentous bacteria cover the seafloor around these craters, and the vents are characterized by voluminous gas streaming (most likely CO₂ bubbles) through sulfur-cemented ash.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 3653 Fluid flow
DE: 3665 Mineral occurrences and deposits
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005