HR: 1330h
AN: T52B-0274    [PDF]
TI: Diagenetic Phase Boundary at the Nankai Trough, SW Japan: Relationship to the Decollement/ Proto-Decollement
AU: * Zscheile, G
EM: genez@es.ucsc.edu
AF: Earth Sciences, UC Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Moore, J C
AF: Earth Sciences, UC Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Bangs, N
AF: Institute for Geophysics, University of Texas, Austin, TX 78759 United States
AU: Gulick, S
AF: Institute for Geophysics, University of Texas, Austin, TX 78759 United States
AU: Moore, G
AF: SOEST, University of Hawaii, Honolulu, HI 96822 United States
AB: In the subduction environment, phase changes within sediments may affect their subsequent deformation during the accretion process. At the Nankai trough, off Cape Muroto, southwest Japan, a phase change from cristobalite to quartz occurs near the depth of the decollement zone, with a prominent seismic reflector marking this diagenetic boundary between the upper and lower Shikoku Basin facies. Outboard of the trench this reflector is initially at greater depth than the projected proto-decollement but migrates upward to transgress it before reaching Ocean Drilling Program Site 1173 in the landward direction. This effectively encases the entirety of the decollement in a lithology depleted in cristobalite and enriched in quartz. Creation of a depth section within a three-dimensional seismic reflection volume enabled this diagenetic reflector to be mapped relative to the oceanic basement reflector, the seafloor reflector, and intervening stratigraphic reflectors. Within areas of recent sedimentation in the trench the diagenetic reflector diverges from the basement reflector and rises vertically in the section. This upward migration of the diagenetic reflector follows a similar upward migration of the isotherms. Thermal gradients in the Muroto region are increased by proximity to the Shikoku Basin paleo-spreading center axis. At subduction regions with lower thermal gradients the cristobalite zone could be expanded to greater depths, allowing sediments untransformed by this diagenetic process to be incorporated into the toe of the prism and potentially altering initial accretionary structures.
DE: 3099 General or miscellaneous
SC: Tectonophysics [T]
MN: 2003 Fall Meeting