HR: 1340h
AN: T23C-1545    [Abstracts]
TI: Climatic and lithologic influences on erosional efficiency in Fiordland, New Zealand
AU: * Clarke, B A
EM: brian@crustal.ucsb.edu
AF: University of California Santa Barbara, Dept of Earth Science, Santa Barbara, CA 93106,
AU: * Clarke, B A
EM: brian@crustal.ucsb.edu
AF: Institute for Crustal Studies, UCSB, Santa Barbara, CA 93106,
AU: Burbank, D W
EM: burbank@crustal.ucsb.edu
AF: University of California Santa Barbara, Dept of Earth Science, Santa Barbara, CA 93106,
AU: Burbank, D W
EM: burbank@crustal.ucsb.edu
AF: Institute for Crustal Studies, UCSB, Santa Barbara, CA 93106,
AB: Landscape evolution in collisional orogens is predominantly driven by spatial and temporal patterns of climatically induced differential erosion in concert with tectonic forcing. Here we investigate the influence of climate, lithology, topography and the primary erosive processes on the landscape morphology of Fiordland, South Island, New Zealand. Spatial patterns of differential erosion, derived from detrital cosmogenic radionuclides (CRNs), across the width of Fiordland reveal an inverse relationship with rainfall gradients. Erosion rates appear highest in the east and decrease towards the rain-soaked west coast. This decoupling of basin averaged erosion rates and modern rainfall gradients suggest that Fiordland morphology is not controlled by stream-power styled river incision. We suggest instead, that glacial and peri-glacial processes are the primary erosive agents governing landscape morphology of the region. Correlation of topographic swath profiles and paleo-ELA gradients, determined from cirque outlets, indicate that the elevation of the mean and maximum topography may be controlled by long-term average gradients in the paleo-ELA. Hypsometric analysis of the range indicates that the amount of landmass diminishes significantly above the paleo-ELA. Slope-altitude distributions reveal that hillslopes steepen with elevation to reach and maintain threshold slopes above the paleo-ELA. The correlation of topographic profiles, hypsometry, and slope distributions with paleo-ELA gradients suggests that topographic limits and the spatial distribution of threshold hillslopes may be controlled by a glacial- or peri-glacial buzzsaw process. The lithologic influence on morphology and erosional efficiency is dominated by the degree of fracturing within underlying bedrock. Initial measurements of bedrock fracture densities in the shallow subsurface appear to follow broad patterns of catchment averaged erosion rates across the range. Additionally, bedrock fracture densities show an altitudinal dependence, with increased fracturing above modern snowline. The eastward verging topographic asymmetry of the range and the similarity in spatial patterns of erosion derived from detrital CRNs and long-term denudation patterns from thermochronologic data suggest that spatial patterns of erosion and the resulting orogenic geometry are controlled by differential patterns of surface uplift raising high peaks into an altitude dependant zone of enhanced erosional efficiency.
DE: 1105 Quaternary geochronology
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 1824 Geomorphology: general (1625)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting