HR: 1340h
AN: T23C-0572    [Abstracts]
TI: Structural and Geomorphic Constraints on the Evolution of Active Thrusting in the Mackenzie Basin, South Island, New Zealand
AU: * Amos, C B
EM: cbamos@crustal.ucsb.edu
AF: Department of Earth Science, 1006 Webb Hall, University of California, Santa Barbara, CA 93106 United States
AU: Burbank, D W
EM: burbank@crustal.ucsb.edu
AF: Department of Earth Science, 1006 Webb Hall, University of California, Santa Barbara, CA 93106 United States
AU: Read, S A
EM: S.Read@gns.cri.nz
AF: Institute of Geologic and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6009 New Zealand
AB: Using geomorphic markers to quantify deformation along active thrust faults has the potential to yield critical insight into the evolution of thrust systems as well as into tectonic and surface process interactions inherent in actively deforming landscapes. Because the sequential kinematic development of ancient thrust systems is commonly hard to reconstruct, progressively deformed geomorphic features serve as indispensable records of both the incremental and integrated strain fields incurred through active thrusting. In the Mackenzie Basin of New Zealand, folded and faulted glacial outwash surfaces and fluvial terraces along the active Ostler and Irishman Creek faults provide constraints on aspects of the deformational style and subsurface fault geometry, as well as the rates, timing, and magnitude of deformation. Detailed field mapping and strike-perpendicular differential GPS surveying of deformed outwash and strath surfaces developed over each fault segment reveals folding characterized by progressively rotated backlimbs of varying wavelength and abrupt, steeply-dipping fold forelimbs. Through construction of observationally based kinematic models for fold and thrust development, we interpret progressive backtilting of fold limbs up to 6 degrees and near-fixed fold hinges as reflecting deformation over listric thrusts rooted at depth into planar, basement-involved thrust ramps. Structural mapping of Neogene strata and Mesozoic basement exposed in the hangingwall of the Ostler fault also suggests that variations in the wavelength of folding and the surface expression of deformational style primarily reflect pre-existing basin architecture and the depth of Tertiary basin fill. Results of preliminary optically stimulated luminescence dating of fluvial silts preserved in terrace fill along the Ostler fault bracket uplift rates for both faults at or below 1 mm/yr, consistent with previously reported Quaternary slip rates east of the central Southern Alps.
DE: 1824 Geomorphology: general (1625)
DE: 8005 Folds and folding
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: Fall Meeting 2005