DISTINCTIVE TRANSIENT RESPONSES OF ACTIVE OROGENIC WEDGES TO LONG-TERM CHANGES IN CLIMATE AND ACCRETIONARY FLUX

Active orogenic wedges are predicted to exhibit a distinctive transient response to long-term changes in either climate state or tectonic accretionary flux in each of total erosional efflux (Fe), topographic relief (R), and rock uplift ( U ) relative to the geoid. Only responses to long-term changes in climatic and tectonic are considered here because only perturbations that are sustained for timescales on the order of system response time (typically a few Myr) can significantly influence time-averaged Fe, R, and U. Glacial-interglacial and shorter climate cycles can dramatically influence short-term sediment fluxes, but can only influence average rates of erosion, rock uplift, and average topographic relief under special circumstances. Predictions here are for one- or two-sided, frictional orogenic wedges at critical taper, which is assumed invariant with changes in climate and accretionary flux. Fast isostatic response to erosional unloading and crustal thickening is assumed. The scenario considered is system response to a single step-function change in either the efficiency of erosion (climate) or tectonic accretionary flux (either convergence velocity or thickness of incoming material). Only changes in tectonic accretionary flux can produce a permanent change in the total erosional efflux (Fe) or sediment delivery to basins. Fe, R, and U each change smoothly following a step change in accretionary flux, asymptotically approaching new steady state values. Topographic relief (R) follows similar asymptotic patterns for both tectonic and climatic changes. A step change in erosional efficiency, on the other hand, causes a sudden, spiked change in both Fe and U, which then decay exponentially either back into balance with the accretionary flux, or to a new steady state value, respectively. Thus climatic and tectonic changes should lead to distinctly different records in adjacent sedimentary basins, the width of active deformation, and thermal records of rock exhumation.