HR: 1330h
AN: OS32A-0234    [PDF]
TI: Hydrothermal deposits in the Southern Trough of Guaymas Basin, Gulf of California: Observations and Preliminary Results from the 2003 MBARI Dive Program
AU: * Stakes, D S
EM: debra@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholt Road, Moss Landing, CA 95039-9644 United States
AU: Tivey, M K
EM: mktivey@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Koski, R A
EM: rkoski@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Ortego-Osorio, A
EM: alexo2@imp.mx
AF: Instituto Mexicano del Petroleo, Eje Central Lazaro Cardena 152 Col. San Bartolo Atepehuacan,, Mexico, D.F 07730 Mexico
AU: Preston, C M
EM: preston@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholt Road, Moss Landing, CA 95039-9644 United States
AU: McCulloch, M T
EM: Malcolm.McCulloch@anu.edu.au
AF: The Australian National University, Research School of Earth Sciences, Canberra, ACT 0200 Australia
AU: Nakamura, K
EM: koichi.nakamura@aist.go.jp
AF: AIST, Institute for Marine Resources and Environment, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8567 Japan
AU: Seewald, J
EM: jseewald@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Wheat, C G
EM: wheat@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholt Road, Moss Landing, CA 95039-9644 United States
AU: Wheat, C G
EM: wheat@mbari.org
AF: University of Alaska, Institute of Ocean Sciences PO Box 757520, Fairbanks, AK 99775 United States
AB: During Leg 2 of the 2003 MBARI expedition to the Gulf of California, the ROV Tiburon completed eight dives to active vent fields in the Southern Trough of Guaymas Basin. Six venting areas were investigated in detail. Tiburon operations included (1) sampling mineral deposits that range from mini-chimneys a few centimeters high to 10-meter-tall sulfide-carbonate structures with wide flanges; (2) collection of 90C to 303C methane, carbon dioxide, and hydrogen-rich vent fluids in gas-tight samplers and plume-laden particulates in Niskin samplers; 3) collection of warm (up to 83C) hydrocarbon-rich sediment push cores; 4) long-term monitoring of three vent sites using thermocouple arrays (see adjacent Tivey et al poster) and osmotically-driven fluid samplers. Seventy days later, the ROV returned to recover the thermocouple arrays and ingrown chimneys. At the lowest temperature sites, fluid (up to 90C) discharged from orifices in sediment surrounded by white to yellow microbial mats. Combined Eh-ISUS (InSitu Ultraviolet Spectrophotometer) sensors mounted on Tiburon identified local increases in bisulfide and decreases in the oxidation/reduction potential (a proxy for methane and hydrogen sulfide) associated with these sites. Massive barite chimneys recovered from the margins of moderate-temperature vent sites are permeated with oil. Chimneys from higher temperature sites, in contrast, lack the liquid hydrocarbon component, and are largely composed of calcium carbonate with lesser anhydrite, amorphous silica, barite, pyrrhotite, Mg-silicate, galena, sphalerite, and chalcopyrite. Mineral precipitation at the southernmost site (Toadstool) is characterized by the formation of carbonate-rich flanges directly above a substrate of altered diatomaceous sediment. The upper sediment crust lies above a stockwork of calcite veins. High-temperature structures at Rebecca's Roost and Broken Mushroom have pagoda-like carbonate-rich flanges trapping pools of hydrothermal fluids that facilitate the growth of centimeter-thick layers of euhedral carbonate and pyrrhotite. Rapidly formed, anhydrite-rich chimneys are present at the summit of the pagoda structures. In-situ laser ablation Sr isotopic analyses of calcite and anhydrite indicate that minerals within flanges precipitate from vent fluids with less than 5% seawater dilution, whereas minerals within the more permeable anhydrite-dominant chimneys precipitate from mixtures of vent fluid with up to 70% seawater.
UR: http://www.mbari.org/expeditions/GOC/Mission/leg2.htm
DE: 3035 Midocean ridge processes
DE: 4832 Hydrothermal systems
DE: 8135 Hydrothermal systems (8424)
DE: 8424 Hydrothermal systems (8135)
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting