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Feedbacks among climate, erosion, and tectonics in a critical wedge orogen

^* Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195
^** School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287
^*** Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195

gerard{at}ess.washington.edu

The interactions among climate, erosion, and tectonics have long been of interest to geologists, but have not yet been united into a single theoretical framework. In this study, representations of orographic precipitation and fluvial erosion are combined with the concept of a critical wedge orogen. The idealized framework captures the basic system dynamics. It also allows for a formal analysis of the precipitation and tectonic interactions in terms of feedback factors and gains, and so permits a quantitative comparison of their relative strengths. The constraint of self-similar growth in a critical wedge orogen acts as a tectonic governor, whereby changes in orogen size are strongly damped. We determine that this negative tectonic feedback is stronger than the precipitation feedback, which may be negative or positive depending on whether precipitation increases or decreases with orogen size. For an extreme positive feedback unconstrained runaway growth is possible, ultimately leading to plateau formation. When orographic precipitation leads to a significant rain shadow, there is a strong partitioning of rock uplift rates that favors the wet, windward flank of the orogen. This flank also dominates the response of the whole orogen to changes in climate or tectonic forcing, except in the case where a large fraction of the eroded material is recycled into the wedge. Finally, it is demonstrated that the response time of the orogen depends on the feedbacks, and is proportional to the gain of the system.