THE MORPHOLOGY AND HISTORY OF EXFOLIATION ON PLUTONIC DOMES IN THE SOUTHEASTERN UNITED STATES

Granite 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, 2011). However, there is currently limited, if any, field data regarding the morphology of granite 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 plutonic 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 Escarpment (Rock Face, NC), and in the interior Blue Ridge mountains (Stone Mountain, NC). All generations of exfoliation slabs (e.g. S1=youngest slab) were mapped at five sites, with different aspects, 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 compression strength (via Schmidt Hammer) were measured within ten 20x20cm boxes along a transect at each site. Overall, slab morphologic characteristics were similar for all three domes, with three generations of slabs evident in almost all cases. Although slab thicknesses varied between slab generations and domes, the average slab thickness was generally in the range 5-15 cm (maximum thickness of 166 cm). Compression strength was progressively lower with increasing slab age at all domes. In addition, 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 topographically, and presumably, long-term exhumation history.