THE INTERSECTION OF TECTONICS, CLIMATE AND WEATHERING IN OROGENIC SYSTEMS

Tectonic and surficial processes have important but under-explored relationships with global climate and geochemical cycles, particularly through accelerated weathering in orogenic regions. Quantifying these relationships has proven difficult due to the dynamic feedbacks between weathering rates, local and regional climate, topography and geomorphology. However, in the basic constant-topography case where uplift is balanced by erosion, some headway can be made by considering a profile of weathered material in an essentially steady state. Here we present an analytical model for landscape-scale chemical weathering with an emphasis on the effect of uplift on the total rate of alteration in a weathering profile. Ultimately, it is uplift that exposes fresh continental rock to weathering and so determines the total amount of weatherable primary material on the earth’s surface. The model is parameterized in terms of the ‘effective surface age,’ a time-scale on which weathering processes can occur in a given environment, which allows comparisons of disparate tectonic regimes. The analysis of weathering regimes across tectonic environments addresses questions concerning the balance of chemical and physical alteration, the geochemical impact of mountain-building events, and when a landscape might be considered to be in steady state with respect to a process of interest. Our results suggest that it is tectonically active areas that will have the strongest influence on climate, especially through the release of plant nutrients and the drawdown of atmospheric carbon dioxide.