COMBINING AIRBORNE LIGHT DETECTING AND RANGING (LIDAR) AND OUTCROP DATA TO CHARACTERIZE M- TO KM-SCALE FRACTURE CHARACTERISTICS IN HETEROGENEOUS BEDROCK: PANTHERTOWN VALLEY (PV) AND LOWER HICKORY NUT GORGE (HNG) AREAS, NC

Natural fracture networks can vary within rocks despite having shared recent tectonic and uplift history, which can affect shallow fracture propagation and interaction. Combining high-resolution LiDAR DEMs (NC QL2, 2019) with outcrop analyses allows examination of the relationship between bedrock and fracture network characteristics at a range of scales.

In PV, felsic gneiss overlain by biotite gneiss form an open, upright antiform. Grain shape foliation parallel to compositional layering in the biotite gneiss weakens in felsic gneiss towards the fold axis. Km-scale NW, NNW, and NE linear valleys bounded by exfoliation “shoulders” occur in the felsic gneiss. In outcrop, fractures dip steeply, define NW, NNW, E, orientations, and are more common in the biotite gneiss. LiDAR lineaments interpreted to represent edges of steep bedrock fractures, twice as abundant in the biotite gneiss, define NW, NE, and E sets.

Overall, HNG foliation dips gently SE-SSE. The lower unit is dominantly an “augen” gneiss. The upper unit contains 1-10 m-thickness scale compositional layering. Penetrative grain shape foliation is parallel to compositional layering where present, but foliation intensity varies in the lower unit. Fractures dip steeply and define WNW, NW, N, and NE orientations. LiDAR lineaments in the steeper slopes define similar sets, but in the valleys are dominated by the NE set and are rare in the upper unit.

Ongoing work suggests that bedrock characteristics influenced fracture patterns: the PV valleys formed along fracture clusters in poorly foliated gneiss and fracture height in HNG is inversely related to intensity of compositional layering.