HR: 1330h
AN: T32A-0920    [PDF]
TI: Hydrothermal Venting in the Southern Most Portion of the Mariana Backarc Spreading Center at 12.57 Degrees N
AU: * Wheat, C G
EM: wheat@mbari.org
AF: University of Alaska Fairbanks, 208 O'Neill Building, Global Undersea Research Unit, Fairbanks, AK 99775 United States
AU: Fryer, P
EM: pfryer@hawaii.edu
AF: University of Hawaii, HIGP 1680 East-West Road, Honolulu, HI 96822 United States
AU: Hulme, S
EM: shulme@mlml.calstate.edu
AF: Moss Landing Marine Laboratory, 8242 Moss Landing Road, Moss Landing, CA 95039 United States
AU: Becker, N
EM: nbecker@soest.hawaii.edu
AF: University of Hawaii, HIGP 1680 East-West Road, Honolulu, HI 96822 United States
AU: Curtis, A
EM: acurtis@hydro.biol.wwu.edu
AF: Western Washington University, Biology Deptartment, Bellingham, WA 98225 United States
AU: Moyer, C
EM: cmoyer@hydro.biol.wwu.edu
AF: Western Washington University, Biology Deptartment, Bellingham, WA 98225 United States
AB: The southernmost portion of the Mariana Trough is a complex zone of deformation and magmatism. The centerpiece of the trough is the Malaguana-Gadao Spreading Center Ridge, which has a morphology that is inflated relative to all of the other spreading segments in the Mariana Backarc Basin. This inflated morphology is similar to that of the EPR and is consistent with a high rate of eruption. Samples of lavas from the spreading center are island arc tholeiites, which typically contain higher concentrations of CO2 relative to MORBs. In February 2003 the NOAA VENTS program conducted two CTD tow-yos in this area, revealing a hydrothermal plume consistent with the presence of a high temperature hydrothermal site. In May 2003 we used the ROV Jason II to survey a hydrothermal site at 12 degrees 57.214'N, 143 degrees 37.147'E in a water depth of ~2860 m. Here we collected vent fluids, sulfides, basalt, microbial mats, and macrofauna. Two styles of venting were identified within an 80 m by 70 m area. Higher temperature venting was located in cracks among extinct mounds that were 2-5 m high and wide and are nearly monomineralic (sphalerite) in composition. The exterior is soft and vuggy in contrast to the interior that has crystalline layers with bladed habit lining the orifices. Maximum temperatures of 248 degrees C were recorded 30 cm into these cracks, which were covered with abundant large provannid snails, Alvinoconcha Hessleri, and crabs. In contrast, lower temperature diffuse venting (77 degrees C) emanated from mounds that have a porous structure that is composed of amorphous iron oxide and opal. These mounds are covered with microbial mats, which exhibit a high degree of biomass as detected by Cyto-13 nucleic acid epifluorescent staining. Filament and amorphous particulate morphotypes are observed in association with microbial cells, but sheaths have not been detected. These mats have a morphology that is similar to that of neutrophilic Fe-oxidizing bacteria. Fluid chemistry is consistent with a single source and with other back-arc derived hydrothermal fluids that are enriched in alkalinity relative to bottom seawater. Extrapolated concentrations per kg of seawater are 0 mmol Mg, 36.2 mmol Ca, 7.3 mmol alkalinity, 544 chlorinity, 414 mmol Na, 32.2 mmol K, 0 mmol sulfate, 165 umol Sr, and 575 umol Li. Additional analyses are ongoing.
DE: 1030 Geochemical cycles (0330)
DE: 1065 Trace elements (3670)
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 3035 Midocean ridge processes
DE: 4832 Hydrothermal systems
SC: Tectonophysics [T]
MN: 2003 Fall Meeting