HR: 16:45h
AN: V54A-04    [Abstracts]
TI: Hydrothermal Mineralization Along the Volcanically Active Mariana Arc
AU: * de Ronde, C E
EM: Cornel.deRonde@gns.cri.nz
AF: Institute of Geological & Nuclear Sciences, 30 Gracefield Rd., Lower Hutt,, Box 31-312 New Zealand
AU: Hein, J R
EM: jhein@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS999, Menlo Park, CA 94025-3591 United States
AU: Embley, R W
AF: NOAA/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Stern, R J
AF: University of Texas at Dallas, Geosciences Dept., Box 830688, Richardson, TX 75083-0688 United States
AB: In March and April, 2004, ROPOS ROV dives took place from the R/V T.G. Thompson along the volcanically active Mariana arc to ground truth CTD data collected a year earlier that indicated hydrothermal activity. Dives took place on seven volcanoes, six of which showed hydrothermal activity. We present data on samples collected from NW Rota-1 ($14\deg$, 36'N, $144\deg$, 46'E), E. Diamante ($15\deg$, 56'N, $145\deg$, 41'E), and NW Eifuku ($21\deg$, 29'N, $144\deg$, 03'E), the three sites most studied. All the hydrothermal systems found are associated with volcano summits, or with resurgent domes inside a caldera. Brimstone vent at NW Rota-1 provided a dramatic display of thick, bellowing, yellow plumes that contained ash and molten sulfur. This site occurs at 500 m water depth and clearly shows closely associated magmatic-hydrothermal discharge. Sulfur was the dominant hydrothermal mineral deposited around the vent and occurs as spheres in the surrounding volcaniclastic sediment, fracture fill and veins, and massive deposits. The Black Forest vent field at E Diamante consists of a sulfide-sulfate chimney system developed at about 650 m water depth. This is the only mature system discovered and consists of numerous tall (up to 9 m) chimneys. The measured fluid temperature of $240\deg$ C produces boiling at the depth of the vents. The chimneys and mounds are composed of varying amounts of pyrite, sphalerite, chalcopyrite, barite, and anhydrite. Hydrothermal Mn oxides occur on the surface of inactive chimneys. This mineralogy contrasts with the other two systems, which deposit sulfur as the dominant hydrothermal product. The Cu-Zn-Fe-Ba mineralization is perhaps largely controlled by water/rock interaction. A unique hydrothermal field (Champagne field) was found at NW Eifuku where liquid CO$_{2}$ is discharging from focused- and diffuse-flow vents at 1600 m water depth. The focused-flow vents consist of small chimneys and mounds up to a meter high that are composed of sulfur and yet to be identified minerals. Sulfides were not recovered from this site. At Champagne, sulfur also occurs as crusts on the surface of sediment in areas of diffuse-flow venting, as fracture fill and veins, and as massive deposits. The dominant characteristics of the hydrothermal mineralization along the Mariana arc are shallow-water systems, highly permeable rocks, gas (SO$_{2}$, H$_{2}$S, CO$_{2}$)-rich discharge, and magmatic-hydrothermal systems controlled by the depth-to-boiling-point curve. These characteristics result predominantly in the subsurface deposition of sulfide mineralization, with E Diamante being the exception.
DE: 8424 Hydrothermal systems (8135)
DE: 4815 Ecosystems, structure and dynamics
DE: 4832 Hydrothermal systems
DE: 4803 Bacteria
DE: 3045 Seafloor morphology and bottom photography
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting