Rejuvenation of Appalachian topography caused by subsidence-induced differential erosion

Abstract

Topographic relief continued to develop in the Appalachian Mountains, eastern USA, long after the tectonic forces that created the range had become inactive. Numerical modelling and reconstructions of sediment deposition in the Gulf of Mexico suggest that the topographic relief was rejuvenated by subsidence-induced differential erosion caused by sinking of the subducted Farallon slab in the underlying mantle. In ancient orogens, such as the Appalachian Mountains in the eastern United States, the difference between the high and low points—topographic relief—can continue to increase long after the tectonic forces that created the range have become inactive. Climatic forcing1 and mantle-induced dynamic uplift2,3 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 Mexico4, 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 Mexico4 and western Atlantic5 correlate with enhanced erosion in the Appalachian Mountains during the Miocene epoch, caused by dynamic tilting of the continent. The model predicts 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 200 m of elevation. I propose that dynamically induced continental tilting may provide a mechanism for topographic rejuvenation in ancient orogens.