Rejuvenation of Appalachian topography due to subsidence induced differential erosion

Thursday, 18 December 2014: 2:40 PM
Lijun Liu, University of Illinois at Urbana-Champaign, Champaign, IL, United States
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 forcing and mantle-induced dynamic uplift are proposed to 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 Appalachian Mountains during the Miocene epoch, caused by dynamic tilting of the continent. Calculations show that such subsidence-induced differential erosion caused flexural-isostatic adjustments of Appalachian topography that led to the development of both relief and elevation. I propose that dynamically induced continental tilting may provide a mechanism for topographic rejuvenation in ancient orogens.