HR: 1330h
AN: T22A-0493    [PDF]
TI: Oblique Strike-Slip Faults and Structural Geomorphology: new Insights From the Plate Boundary Transfer Zone, NE South Island, New Zealand
AU: * Pettinga, J R
EM: jarg.pettinga@canterbury.ac.nz
AF: Geological Sciences,, University of Canterbury, P.B. 4800,, Christchurch, Ct 8004 New Zealand
AB: Temporal and spatial variations in topographic loading directly affect near-surface stress field perturbations controlling fracture propagation and orientation, as well as fault zone behaviour and evolution. While some end-member styles of transpressional deformation are well documented by laboratory modelling and from field examples, fault-slip is often complex, and invariably accompanied by progressive uplift and mountain building. There are few field studies documenting the critical interdependence of fault zone evolution and tectonically-driven mountain building. Under transpressive conditions a combination of compressive loads generated by the regional stress field coupled with the asymmetric additional loading created by the uplifted topography tends to extrude a wedge of material out of range front shear zones producing an anomalous sense of normal surface displacement. The combination of footwall splays and partitioning of strike-slip on the steep hanging wall side of the whole fault zone, creates a wedge of weakened rock dominated by inclined shear zones dipping into the hillside. Conversely if conditions give rise to a relaxation and a change to extension, the pre-existing steep reverse faults are optimally oriented to reverse slip and act as normal faults so that the whole wedge slides in under the hanging wall. The development of an inclined wedge on non-vertical faults is specific to this mode of deformation. Integration of structural geometry and geomorphic evolution in the analysis of tectonically active regions has pragmatic implications for paleoseismic studies, where surface displacements are only indirectly related to actual slip components at seismogenic levels. A further question is how does geomorphic evolution of a fault-driven landscape (e.g. valley incision, large deep-seated landsliding) influence upper crustal fault zone architecture and visa versa. Detailed field observations from the plate boundary transfer zone in NE South Island has formed the basis of related structural models. These illustrate the way in which slip along range front fault zones is distributed in complex 3D deformation both within segments and at segment boundaries, and the way topography influences these processes.
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8020 Mechanics
DE: 8107 Continental neotectonics
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting