HR: 1340h
AN: T13B-0466    [Abstracts]
TI: Composition and Dehydration of Clay Minerals from Hemipelagic Sediments at Hydrate Ridge, Cascadia Subduction Zone
AU: * Basu, N
EM: nbf78@mizzou.edu
AF: University of Missouri, Department of Geological Sciences, Columbia, MO 65211 United States
AU: Underwood, M B
EM: UnderwoodM@missouri.edu
AF: University of Missouri, Department of Geological Sciences, Columbia, MO 65211 United States
AU: Torres, M
EM: mtorres@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvalis, OR 97331 United States
AU: Slaughter, S A
T13B-0466 AF: University of Missouri, Department of Geological Sciences, Columbia, MO 65211 United States
AU: Slaughter, J B
T13B-0466 AF: University of Missouri, Department of Geological Sciences, Columbia, MO 65211 United States
AB: Among the significant results of shipboard pore-water analyses during ODP Leg 204 (Hydrate Ridge) are chloride concentration profiles from Site 1252 to Site 1245. The profiles show progressive depletions of chloride at depth (relative to ocean bottom water), which is consistent with diffusion from a deeper-seated fluid source within the accretionary complex. As the distance from and depth beneath the prism toe increase, temperature and reaction time should promote progressive smectite dehydration within the postulated fluid source. To test this idea, we completed semi-quantitative analyses of clay-mineral composition by X-ray diffraction. Oriented aggregates of the clay-sized fractions (<2 microns) were used to estimate relative percentages of smectite, illite, and chlorite (+kaolinite). For the most part, stratigraphic variations in clay-mineral composition are modest, and there are no significant differences among the seven sites that were included in the study. On average, early Pleistocene to Holocene trench-slope and slope-basin deposits contain 29% smectite, 31% illite, and 40% chlorite (+kaolinite). Late Pliocene to early Pleistocene strata from the underlying accretionary prism contain moderately larger amounts of smectite, with average values of 38% smectite, 27% illite, and 35% chlorite (+kaolinite). There is no evidence of clay mineral diagenesis. The expandability of smectite is, on average, equal to 64%, and there are no systematic variations in expandability as a function of burial depth or depositional age. The absence of shallow clay-mineral diagenesis is consistent with the sample depths, where maximum temperatures are only 24° C to 33° C.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3004 Gas and hydrate systems
DE: 3022 Marine sediments: processes and transport
DE: 3036 Ocean drilling
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005