HR: 13:40h
AN: T33D-01    [Abstracts]
TI: Timescale of Orogen Response to Tectonic and Climatic Forcing
AU: * Whipple, K X
EM: kxw@mit.edu
AF: Dept. Earth, Atmospheric, and Planetary Science, MIT, Cambridge, MA 02139 United States
AU: Meade, B J
EM: meade@rupture.harvard.edu
AF: Dept. of Earth and Planetary Science, Harvard, Cambridge, MA 02139 United States
AB: We have recently published an analytical solution that quantifies the strength of coupling among climate, topography, erosion, and deformation in frictional orogenic wedges at mass flux steady state. Here we extend this work to address the transient evolution of frictional orogenic wedges in response to changes in climatically controlled erosional efficiency and tectonically driven accretionary flux. Interestingly, the coupling between climate and tectonics is shown to be stronger during transients than at steady state. Significant, potentially diagnostic, differences are seen in orogen response to climatic versus tectonic perturbations. By assuming that wedge geometry, during growth and decay, is self-similar, and that response time is controlled by mass balance not drainage basin rearrangement, we derive an approximate analytical solution for orogen response time. Following a step-function change in either erosional efficiency or accretionary flux, wedge cross-sectional area asymptotically approaches a new steady state condition. The transient evolution of wedge cross-sectional area is approximately exponential, such that orogen response time can be characterized by a half-life. Remarkably, the transient response time is determined primarily by the erosional efficiency associated with the final climate state, and only weakly influenced by the initial conditions, the magnitude of the climatic or tectonic perturbation, and the accretionary flux. A robust implication is that, for a given set of initial conditions, orogen response to an increase in the erosional efficiency will be faster than that to a change in accretionary flux, which, in turn, will be faster than that to a decrease in erosional efficiency. The transient response time is determined to have a sub-linear dependence on the details of the erosion rule and the rheology of the orogenic wedge, varying by less than a factor of two for a wide range of model parameters.
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 8122 Dynamics, gravity and tectonics
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting