RELATING LIDAR LINEAMENTS TO BEDROCK STRUCTURES IN THE PANTHERTOWN VALLEY AND HICKORY NUT GORGE AREAS OF THE SOUTHWESTERN NORTH CAROLINA BLUE RIDGE

Several hypotheses link major topographic lineaments and brittle structures in the southern Appalachians with geologically young uplift. Kinematic analyses are needed to test these hypotheses, but can be hampered by poor exposure and/or bedrock that behaved heterogeneously during brittle deformation. “Bare earth” images derived from high-resolution airborne LiDAR reveal abundant evidence of fracture sets in the Blue Ridge of southwestern North Carolina, but their relationships to structural, geologic, and geomorphologic domains are as yet poorly understood.

Lineaments (fracture traces) identified in ground model images derived from NC statewide airborne LiDAR (2005, 2013) have been compared with geomorphologic domains and results of targeted detailed geologic mapping (lithology, m-scale brittle and ductile structures) in two regions where 0.5 km-wide NW linear valleys intersect ~NE-trending, 100 km-long, E-facing escarpments. Both study areas have similar bedrock lithologies and relatively simple km-scale ductile structures. The valley lineaments are not observed to correspond with lithology, grain size/distribution, or ductile structures, so the preferential weathering is interpreted to indicate zones of intense fracturing. In the Panthertown Valley area, felsic gneiss overlain by biotite gneiss form a km-scale, refolded, open, upright antiform. Foliation intensity weakens towards the fold axis. Km-long NW, NNW, and NE linear valleys incise felsic gneiss in the core of the fold, but narrow or fade across the transitional lithologic contact. Fractures other than exfoliation are rarely observed, and dip steeply. In the Hickory Nut gorge area, felsic gneiss overlain by interlayered biotite and amphibolite gneiss exhibit foliation, of varying intensity, dipping gently SE-SSE. Major, 10s km-long, topographic valleys trend NW and NE. Fractures in outcrop are often steep and strike NW, NE, and ESE. Ongoing work in both field areas indicates that orientation sets of LiDAR lineaments (fracture traces) are overall consistent with those of overall outcrop fracture and topographic lineaments. However, km-scale variations in LiDAR lineament orientation frequencies are cryptic unless closely spaced fractures inferred from the valley lineaments are included.­