| Rock domes and associated surface-parallel exfoliation joints are evident in all tectonic and climatic settings, including the Blue Ridge and Piedmont provinces of the southeastern United States. Although large-scale dome exfoliation is traditionally attributed to pressure release via erosional unloading, alternative hypotheses exist for its formation; e.g. tectonic or insolation-driven deformation (e.g. Martel 2006; Collins and Stock 2016). However, there are currently limited, if any, field data regarding the morphology of such domes and their associated exfoliation slabs that might serve to test these hypotheses. The purpose of this study is to characterize the morphologic, topographic, and mechanical weathering characteristics of exfoliation slabs on three domes in the southeastern United States. The domes are located in a roughly linear transect across the Blue Ridge Escarpment (~36° latitude), including locations in the Piedmont (40 Acre Rock, SC), within the foothills (Rock Face, NC), and the in the Blue Ridge mountains (Stone Mountain, NC). All generations of exfoliation slabs (e.g. S1=most recently exposed, lowest, S2= the next overlying slab) were mapped at five sites, each characterized by a different aspect, for each dome. Slab thickness measurements were obtained for each slab generation at each site at each dome. To characterize the relative age of each slab generation, weathering characteristics including crack morphology and slab surface compressional strength (via Schmidt Hammer) were measured within ten 20x20cm boxes along a transect at each site. Overall, slab morphological characteristics are similar for all three domes, with three generations of slabs present at the majority of sites. Although slab thicknesses vary somewhat between slab generations and domes, the average slab thicknesses are similar, in the range 15.58cm to 23.82cm (maximum thickness of 166 cm). Compressional strength is progressively lower with increasingly older slab generations at all domes, indicating a higher degree of weathering, with increasing slab generation. This result and other weathering characteristics provide evidence that the formation of each slab generation occurred at distinct, separate intervals. Overall, these preliminary analyses provide evidence that dome exfoliation processes are similar spatially and temporally for the three domes, despite their distinct differences in topography, and presumably, long-term exhumation history. |
