HR: 0830h
AN: T21C-0462    [PDF]
TI: Rates of Fault Growth and Landscape Development in Central Otago, New Zealand
AU: * Bennett, E R
EM: bennett@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Bullard Laboratories, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Youngson, J H
EM: john.youngson@stonebow.otago.ac.nz
AF: Department of Geology, University of Otago, P.O.Box 56, Dunedin, 9001 New Zealand
AU: Jackson, J
EM: jackson@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Bullard Laboratories, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Norris, R J
EM: richard.norris@stonebow.otago.ac.nz
AF: Department of Geology, University of Otago, P.O.Box 56, Dunedin, 9001 New Zealand
AU: Raisbeck, G
EM: raisbeck@csnsm-in2p3.fr
AF: Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, IN2P3-CNRS, Batiment 108, Orsay, 91405 France
AU: Yiou, F
AF: Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, IN2P3-CNRS, Batiment 108, Orsay, 91405 France
AB: Central Otago is a region dominated by NE trending anticlinal ridges which form above buried reverse faults. Slow average velocities (3-5 mm ${\rm yr}^{-1}$ from GPS), coupled with low erosion rates due to the aridity of the region make this an ideal area to study landscape forming processes over unusually long time periods. DEM and drainage pattern analysis of the Rough Ridge system shows that South Rough Ridge has propagated northwards, pushing the Oliverburn stream to the north as it does so. This stream has cut strath terraces, which record the history of the progressive movement of the stream. After abandonment, these terraces are uplifted and warped by the continuing growth of the ridge. Quartzite boulders on the terrace surfaces were analysed for cosmogenic $^{10}$Be and $^{26}$Al in order to gain an approximate age for the abandonment of each terrace. Whilst the exact time at which a river cuts down and begins to create a new strath terrace may depend on many variables, such as a change in climatic regime, the relative timing of abandonment of all of the terraces must be a proxy for the growth of the ridge, as it is controlled by the movement of the stream northwards. The progressive warping of higher terrace surfaces and the lack of terrace surfaces of a similar height in the basin to the east of the range indicates that local, rather than regional, base level changes are the controlling factor of terrace formation. The qualitative interpretation of the geomorphology of this region is confirmed by the cosmogenic results. On the tip of South Rough Ridge we obtain an average uplift rate of 0.10-0.15 mm ${\rm yr}^{-1}$ and a lateral propagation rate of 1.0-2.0 mm ${\rm yr}^{-1}$ averaged over the last 450,000 years. On neighbouring Rough Ridge, we also obtain minimum $^{10}$Be ages of 1 Myr, indicating extremely low erosion rates in this area.
DE: 5415 Erosion and weathering
DE: 8005 Folds and folding
DE: 8040 Remote sensing
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting