REJUVENATION OF APPALACHIAN TOPOGRAPHY CAUSED BY SUBSIDENCE-INDUCED DIFFERENTIAL EROSION

Development of topographic relief over ancient, inactive orogens such as the Appalachians, remains an outstanding question. Climatic forcing and mantle-induced dynamic uplift could drive formation of relief, but clear evidence is lacking in the Appalachian Mountains. Here I use a numerical simulation of dynamic topography in North America, combined with reconstructions of the sedimentation history from the Gulf of Mexico, to show that rejuvenation of topographic relief in the Appalachian Mountains since the Palaeogene period could have been caused by mantle-induced dynamic subsidence associated with sinking of the subducted Farallon slab. Specifically, I show that patterns of continental erosion and the eastward migration of sediment deposition centres in the Gulf of Mexico closely follow the locus of predicted dynamic subsidence. Furthermore, pulses of rapid sediment deposition in the Gulf of Mexico and western Atlantic correlate with enhanced erosion in the Appalachians during the Miocene epoch, caused by dynamic tilting of the continent. The model suggests that such subsidence-induced differential erosion caused flexural-isostatic adjustments of Appalachian topography that led to the development of 400 m of relief and more than 200m of elevation. I therefore propose that dynamically induced continental tilting may provide a mechanism for topographic rejuvenation in ancient orogens. We are currently working on a quantitative prediction of the topographic evolution of eastern United States, with the hope of better constraining the pattern of dynamic topography, fluvial system migration, and orogenic evolution.