HR: 15:10h
AN: T33D-07    [Abstracts]
TI: Rocks, Rivers, and Rain: Controls on Exhumation in Orogenic Belts?
AU: * Stolar, D B
EM: dstolar@u.washington.edu
AF: Department of Earth and Space Sciences University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Roe, G H
EM: gerard@ess.washington.edu
AF: Department of Earth and Space Sciences University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Willett, S D
EM: swillett@u.washington.edu
AF: Department of Earth and Space Sciences University of Washington, Box 351310, Seattle, WA 98195 United States
AB: Coupling between tectonics, erosion and climate is evident in many aspects of orogen evolution, including the pattern of exhumation observed at the Earth's surface. Indeed, there is strong evidence from numerical modeling studies that the distribution of precipitation is a primary control of the pattern of tectonic deformation. Further, because the exhumation pattern integrates information about the internal mechanisms of orogenesis, it is a useful tool for examining the manner and magnitude of the linkages between tectonics, erosion and climate. Currently lacking from analyses of natural orogens, however, is a sound theoretical understanding of how the components of the coupled system are expected to control the pattern of exhumation. We investigate this question with analytical and numerical models in which critical wedge theory describes the behavior of the tectonic system (e.g., fold-and-thrust belts and small accretionary orogens such as the Olympic mountains of Washington state). Critical wedge theory is arguably the simplest framework in which to consider this question; it predicts that the mean topographic slope in the direction of convergence maintains a critical taper angle and that perturbations are compensated by tectonic deformation. The analytical and numerical models contain different but self-consistent descriptions of surface erosion and tectonic deformation. In the analytical model, critical wedge theory constrains the mean topographic slope, and the stream-power law is used to simulate fluvial erosion. In the numerical model, a planform landscape evolution model, incorporating fluvial erosion and landsliding, is coupled with a model that simulates deformation of a Coulomb-plastic material. The most important difference between the two models is that ridge-valley relief is not allowed to develop in the former, whereas it arises naturally in the latter. With each model, we explore two scenarios: uniform precipitation and non-uniform precipitation with a boxcar increase above a background value. In the first scenario, we find that, 1) the erosion law determines the first-order form of uplift pattern, 2) non-uniform uplift is a natural response to uniform precipitation, and 3) uplift rate correlates well with ridge-valley relief in the numerical experiments. In the case of non-uniform precipitation, the analytical model predicts that the uplift rate increases both within and downstream of the precipitation increase, whereas the numerical model predicts that the uplift response matches the precipitation increase in both form and extent. From these results, we conclude that the uplift pattern in this tectonic framework is controlled primarily by erosion and the distribution of precipitation and that the development of ridge-valley relief has important implications for the form of the uplift and exhumation patterns.
DE: 8100 TECTONOPHYSICS
DE: 8159 Rheology--crust and lithosphere
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting