HR: 1330h
AN: T42D-0966
TI: Spatial Variability of Deformation Front Structures in the Nankai Accretionary Prism
AU: * Heffernan, A S
EM: adam@es.ucsc.edu
AF: Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Moore, C
AF: Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Bangs, N
EM: nathan@utig.ig.utexas.edu
AF: Institure of Geophysics, University of Texas, Austin, TX 78759
AU: Moore, G F
EM: gmoore@Hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, HI 96822 United States
AU: Shipley, T H
EM: tom@utig.ig.utexas.edu
AF: Institure of Geophysics, University of Texas, Austin, TX 78759
AB: The Nankai margin off southwest Japan is characterized by active convergence, a large accretionary prism, and a thick sequence of incoming hemipelagic sediments. In the Moroto area, a 3-D seismic volume images the undeformed stratigraphy of the Shikoku Basin, landward through a protothrust zone, across the frontal thrust, through several prominent imbricate thrusts, and into a zone of large out-of-sequence thrusts. Interpretation of reflectors in the protothrust zone reveals a high degree of structural complexity, as well as along-strike structural variability. In addition to a prominent protothrust, the protothrust zone contains several smaller incipient thrusts oriented parallel to the frontal thrust, conjugate back thrusts, and numerous small normal faults. Seismic data also reveal complex oceanic crust morphology underlying the incoming sedimentary package. This ocean crust is characterized by a linear, trench-normal structural low, which is likely a remnant of its formative spreading process. The high degree of relief in this basement surface suggests that differential compaction may be responsible for similarly oriented normal faults in the overlying Shikoku Basin sequence. Trench-parallel normal faults, however, are more likely the result of flexure of the downgoing plate as it begins to subduct. The linear basement structural low also coincides spatially with a prominent bend in both the frontal thrust and main protothrust. This prominent bend may be part of a regional landward stepping of the frontal thrust to the north. The protothrust zone marks the transition from an undeformed sedimentary sequence to an accretionary prism exhibiting fold and thrust belt structure controlled by an underlying decollement. Reflectors in the Shikoku Basin sequence, seaward of the main protothrust, show subtle signs of compressional deformation and better constrain the location of the onset of slip on the decollement.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8155 Plate motions--general
SC: T
MN: 2001 AGU Fall Meeting