HR: 11:20h
AN: T12B-05    [Abstracts]
TI: Nankai Stress History and Implications for an Overpressured D‚collement
AU: * Moran, K
EM: kate.moran@uri.edu
AF: Graduate School of Oceanography and Dept. of Ocean Engineering, University of Rhode Island, Narragansett, RI 02882 United States
AU: O'Regan, M
EM: oregan@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882 United States
AB: The Nankai Trough, formed from the subduction of the Shikoku Basin beneath the island arc of southwestern Japan, is a relatively young accretionary complex converging at a rate of ~4 cm/yr [Shipboard Scientific Party, 2001a]. The region was studied during the Deep Sea Drilling Project and on three Ocean Drilling Program (ODP) Legs-131, 190 and 196. Three sites visited during these Legs form a single cross-margin transect (dubbed the Muroto Transect) that traverses the leading edge of the Nankai accretionary prism, from seaward of the deformation front at Site 1173, to close to the deformation front (Site 1174), and landward to the first frontal thrust (Site 808). The d‚collement, which forms the major boundary between the converging plates, occurs within the Lower Shikoku Basin stratigraphic unit. The ODP sites were drilled and cored to depths below the d‚collement (Sites 808 and 1174) and the proto-d‚collement (Site 1173). Here we present consolidation test results [Moran et al., 1993] that are consistent with porosity-depth functions from core and log measurements for the Lower Shikoku Basin sediments, assuming that the d‚collement is an overpressured seal. At 1173, where a true d‚collement has not yet formed, moderate fluid overpressures occur that can be fully attributed to high turbiditic sedimentation rates. Forward modeling of this site into the deformation front over a period of ~300 ky shows that the present 1173 porosity-depth function matches the porosity-depth function at 1174. These results suggest that the young d‚collement on the Muroto Transect at the deformation front and landward is highly overpressured and forms a seal to sediments below that can be classically modeled as a one-dimensional consolidation system.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 5114 Permeability and porosity
DE: 8168 Stresses: general
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005