DIFFERENTIAL MOVEMENT OF DISCRETE CRUSTAL BLOCKS DURING NEOGENE UPLIFT OF THE SOUTHERN APPALACHIAN BLUE RIDGE PROVINCE
HILL, Jesse S., Department of Geological Sciences, University of North Carolina at Chapel Hill, Mitchell Hall, Campus Box 3315, Chapel Hill, NC 27599 and STEWART, Kevin G., Department of Geological Sciences, Univ of North Carolina, 122 Mitchell Hall, CB 3315, Chapel Hill, NC 27599-3315, hilljs@live.unc.edu
The difference in elevation between the Blue Ridge province of western North Carolina and the adjacent Valley-and-Ridge and Piedmont provinces is commonly greater than 1000 meters. There is a growing body of evidence supporting the idea that this elevation difference is at least in part due to Neogene uplift of the Blue Ridge. Gently folded Oligocene rocks underlying undeformed Miocene strata near the southern extent of the Blue Ridge in Georgia and Alabama (Dennison and Stewart, 2001) and transient knickpoints of the Cullasaja River basin of southwestern North Carolina (Gallen et. al, 2013) suggest a Neogene-aged uplift event in the southern Appalachians. In Pennsylvania, knickpoints along the Susquehanna River are upstream of zones with high erosion rates and downstream of zones with low erosion rates, based on 10Be exposure ages (Miller et al., 2013). Depositional records along the US Atlantic coast (Poag and Sevon, 1989; Pazzaglia and Brandon, 1996) and the Gulf of Mexico (Galloway et al., 2011) contain four pulses of increased sedimentation in the Appalachians since the Triassic, with the last pulse occurring ~20 Ma. Gallen et. al. (2013) suggested that the Miocene uplift that affected western North Carolina was epirogenic and consistent across the region. If this is the case, the knickpoints found in the Cullasaja should exist in at similar elevations along the length of streams everywhere in region. Longitudinal profiles extracted from dozens of stream networks throughout the Blue Ridge suggest that this is not the case.
Distinct topographic styles and stream profile geometries are used as proxies for the relative timing of uplift of distinct zones of the Blue Ridge province of western North Carolina. A discretized slope map highlights areas with low elevation and low slope (these are commonly valleys and topographic lineaments), high elevation and low slope (possible pre-Miocene landscape), and high elevation and high slope (possible post-Miocene landscape). This type of map shows distinct zones of terrain, some of which are bounded by topographic lineaments. Varying degrees of disequilibrium along streams in the Blue Ridge of western North Carolina suggest that the topography was rejuvenated by motion of discrete crustal blocks rather than as broad, coherent uplift.
