HR: 10:35h
AN: U32A-02    [Abstracts]
TI: Old transient landscapes and surface processes: Multiple cosmogenic nuclide and sediment yield data from the Central Andes of northern Chile
AU: * Kober, F
EM: kober@erdw.ethz.ch
AF: Institute of Geology & Institute of Isotope Geology, ETH Zurich, Sonneggstr. 5, Zurich, 8092
AU: Ivy-Ochs, S
EM: ivy@phys.ethz.ch
AF: Institute of Particle Physics, ETH Zurich, Honggerberg, Zurich, 8093
AU: Ivy-Ochs, S
EM: ivy@phys.ethz.ch
AF: Institute of Geography, Universitaet Zurich-Irchel , Zurich, 8057
AU: Schlunegger, F
EM: schluneg@geo.unibe.ch
AF: Institute of Geology, University of Bern, Baltzerstr. 1, Bern, 3012
AU: Zeilinger, G
EM: zeilinger@consulting-geologists.com
AF: Institute of Geosciences, University of Potsdam, Postfach 60 15 53 , Potsdam, 14415
AU: Kubik, P W
EM: kubik@phys.ethz.ch
AF: PSI/ c/o Institute of Particle Physics, ETH Zurich, Honggerberg, Zurich, 8093
AU: Baur, H
EM: baur@erdw.ethz.ch
AF: Institute of Isotope Geology, ETH Zurich, Sonneggstr. 5, Zurich, 8092
AU: Wieler, R
EM: wieler@erdw.ethz.ch
AF: Institute of Isotope Geology, ETH Zurich, Sonneggstr. 5, Zurich, 8092
AB: The desert parts of the Andes of northern Chile are regarded as being one of the oldest landscapes on Earth and hence landscape forming processes must act at very slow rates. These slow rates have promoted controversial ideas on the evolution of the Andean mountain chain and discussions whether climatic or tectonic forces predominate the geodynamic evolution of the Andes. Here we present erosion rates of hillslope interfluves across the slope of the western Central Andes (Arica area, northern Chile) derived from several long-lived terrestrial cosmogenic nuclides (¹⁰Be, ²¹Ne, ²⁶Al). Erosion rates positively correlate with elevation and the historical precipitation record, suggesting a coupling between climate and erosion. In addition, it is suggested that the very old landscapes could be preserved in the western Central Andes thanks to low tectonic activity and the prevailing dry climate. Erosion rates estimated back into the middle to late Miocene are on the order of 10-100cm/My at the hyperarid Western Escarpment (Atacama Desert) and the Costal Cordillera. In contrast, erosion rates for the semiarid Western Cordillera are up to >3000cm/My, at least back into the Holocene/late Pleistocene. Here sediment yield data obtained on a decadal scale indicate denudation rates of a similar order of magnitude. In comparison, erosion rates obtained from long-lived cosmogenic nuclides on hillsope interfluves for the Western Cordillera and those derived from preliminary data (²¹Ne) on catchment wide erosion rates of the Lluta-drainage system yield similar orders of magnitudes. Additionally, catchment wide erosion rates remain largely constant throughout the entire catchment. The analyses of multiple terrestrial cosmogenic nuclides and the use of various "erosion-island" diagrams allowed the identification of system states and of possible complex exposure histories. Complex exposure was identified for non-bedrock samples, such as boulders or amalgamated clast samples. Cosmogenic nuclide concentrations from bedrock samples of the lower Western Escarpment, however, imply near steady-state or transient states over million year timescales likely caused by processes such as episodic bedrock spalling in the cm-scale. Although the surfaces have demonstrably exposed since the Miocene, timescales to achieve cosmogenic nuclide saturation (dynamic equilibrium) and landscape steady states may not be necessarily the same. Nevertheless, landscape forming processes act on very low rates and relief modification is therefore almost negligible.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 4918 Cosmogenic isotopes (1150)
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
SC: Union [U]
MN: Fall Meeting 2005