HR: 16:45h
AN: T44A-04    [Abstracts]
TI: Constraints on the Timing and Kinematics of Deformation Within a Thick-skinned, Inner Forearc Thrust System, Northeastern Japan Margin
AU: * Regalla, C
EM: cregalla@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802, United States
AU: Fisher, D
EM: fisher@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802, United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802, United States
AU: Morell, K
EM: kmorell@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802, United States
AB: New structural and chronologic data from the inner forearc of the northeastern Japan erosive subduction margin provide evidence for Neogene to Quaternary thick-skinned deformation accommodated largely by a high-angle, near-coastal, margin-parallel reverse fault. This structure, the Futaba fault, bounds the exhumed Abukuma massif on the east and places Cretaceous granites in fault contact with Miocene to Pliocene near-shore to terrestrial, tephra-rich sands and silts. Recent exhumation of the massif by slip along the Futaba fault is implied by a regionally extensive footwall syncline, the absence of Neogene sediments in the hanging wall, and high relief on the eastern margin of the massif. New structural data from three transects across deformed footwall units in the central and southern segments of the Futaba fault are used as inputs for forward trishear kinematic modeling. The footwall of the central segment of the Futaba fault is characterized by an open syncline with a steeply dipping to overturned western limb. Toward the south, displacement on the Futaba fault diminishes and dissipates into a gently south-plunging fold within the cover sequence where steeply dipping Miocene units are unconformably overlain by Pliocene growth strata. Dated tephra beds within the pre-growth and growth section at this location bracket the onset of deformation between middle Miocene and early Pliocene. Our results show that these structures are best modeled as the result of deformation associated with the propagation of a steep, west- dipping reverse fault. This interpretation is supported by the orientation of Riedel shears within the fault zone, which are consistent with stress orientations that favor reverse fault motion. The kinematics and time of onset of deformation associated with the exhumation of the Abukuma massif imply a transition to compressive stresses in the inner forearc during the middle Miocene to early Piocene, which may be linked to changes in plate boundary tractions related to Neogene subduction erosion. Thus subduction erosion processes can result in uplift of the inner forearc as a consequence of out-of-sequence thrusting near the margin of the extinct arc.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting