Shear fault-bend folding

Author(s): Suppe, John; Connors, Christopher D.; Zhang, Yikun
Author Affiliation(s): Primary:
Princeton University, Department of Geosciences, Princeton, NJ, United States
Washington and Lee University, United States
Volume Title: Thrust tectonics and hydrocarbon systems
Volume Author(s): McClay, Ken R., editor
Source: AAPG Memoir, Vol.82, p.303-323; International conference on Thrust tectonics, Egham, United Kingdom, April 1999, edited by Ken R. McClay. Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States. ISSN: 0271-8529. ISBN: 0-89181-363-2
Note: In English. Includes appendices. 39 refs.; illus., incl. sects.
Summary: Shear fault-bend folding produces ramp anticlines with very distinctive shapes. They are characterized by long, gentle backlimbs that dip less than the fault ramp, in contrast with classical fault-bend folding. Backlimb dips and limb lengths increase progressively with fault slip, by a combination of limb rotation and kink-band migration. We summarize and apply two simple end-member theories of shear fault-bend folding involving a weak decollement layer of finite thickness at the base of ramp: (1) simple-shear fault-bend folding, in which the layer undergoes an externally imposed bedding-parallel simple shear with no basal fault, and (2) pure-shear fault-bend folding in which this basal layer slides above a basal fault and shortens and thickens above the ramp, with no externally applied bed-parallel simple shear. In the limit of large displacement, the fold geometry in pregrowth strata approaches the geometry of classical fault-bend folding, with a backlimb dip that approaches the ramp dip. However, even in these cases, growth strata may record the history of limb rotation that is characteristic of a shear fault-bend fold heritage. We demonstrate that these theories are in agreement with well-imaged seismic examples from the Nankai Trough and Cascadia accretionary wedges, which show substantial shears (40-65°) over stratigraphic intervals of a few hundred meters.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 16 Structural Geology; 20 Geophysics, Applied; Accretionary wedges; Anticlines; Cascadia Basin; Case studies; Cores; Decollement; Deformation; East Pacific; Faults; Fold and thrust belts; Folds; Geometry; Geophysical methods; Geophysical profiles; Geophysical surveys; Kinematics; Mathematical models; Nankai Trough; North Pacific; Northeast Pacific; Northwest Pacific; ODP Site 808; Ocean Drilling Program; Pacific Ocean; Ramps; Seismic methods; Seismic profiles; Shear; Surveys; Tectonics; Thrust faults; Thrust sheets; West Pacific
Coordinates: N322105 N322111 E1345646 E1345634
Record ID: 2005028969
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.