HR: 0800h
AN: T31A-0482    [Abstracts]
TI: Geochemical and Morphological Characteristics of Metalliferous Deposits at the Endeavour Segment, Juan de Fuca Ridge
AU: * Hrischeva, E
EM: hrischeva@geology.utoronto.ca
AF: Department of Geology, University of Toronto , 22 Russell Street, Toronto, ON M5S 3B1 Canada
AU: Scott, S
EM: scottsd@geology.utoronto.ca
AF: Department of Geology, University of Toronto , 22 Russell Street, Toronto, ON M5S 3B1 Canada
AB: Metalliferous sediments of the Endeavour Segment, Juan de Fuca Ridge originating from fallout of particles from a hydrothermal plume and wasting of sulfide chimneys and their oxidation products, as well as deposits of primary Fe-Si-rich oxyhydroxides, were collected during Keck supported expeditions in 2003 and 2004. The analysis of sediment deposited within 35 m of an actively venting high-temperature chimney at the Main Endeavour Field and containing hydrothermal material derived from a plume fallout indicates that Fe, Cu and Zn settled as sulfides, constituting about 3% of the sediment, and as amorphous phases. The amorphous material is represented by Fe-Si-S phases and black aggregates of variable Fe-Mn-Si-S-P-Ca-Mg-Cu-Zn composition. The association of the amorphous material with biogenic debris and bacteria suggests that microorganisms have enhanced the scavenging of the metals and their settlement near the vents. Fine-grained sulfides, barite and other mineral particles may have been deposited near the vents as zooplankton fecal pellets. Barite and Fe-Mn oxyhydroxides are the hydrothermal phases in the sediments along 1.8 km of the axial valley. The sediments also contain Fe-rich montmorillonite of authigenic origin, illite, chlorite, quartz, feldspar and calcite. The study of a mound of old oxidized sulfides at the Main Endeavour Field shows that patchy accumulations of Fe oxyhydroxides are associated with increased concentrations of Si. It is suggested that the oxidation of sulfides was accompanied by precipitation of primary Fe-Si oxyhydroxides from diffuse low-temperature sources. At the Mothra Field, low-temperature solutions have deposited amorphous Fe-Si-Mn oxyhydroxides containing minor Ca, P, Mg, S, Zn and Cu as well as amorphous material of Fe-Mn-Si-S-P-Zn-Pb composition that are found as an external crust on the wall of an extinct chimney. In the oxyhydroxide deposits, the amorphous material is associated with a variety of mineralized microorganisms, which served as a substrate for its chemical precipitation or in some cases may have mediated the mineralization process. A diversity of unique filamentous, rod-shaped and coccoid microbes was observed in the oxyhydroxides at Mothra.
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460)
DE: 4832 Hydrothermal systems (0450, 1034, 3017, 3616, 8135, 8424)
DE: 4835 Marine inorganic chemistry (1050)
DE: 4863 Sedimentation (1861)
SC: Tectonophysics [T]
MN: Fall Meeting 2005