RADAR CHARACTERISTICS OF SOUTHEASTWARD VERGENT FOLDS AND REVERSE FAULTS IN THE TILLERY FORMATION, CAROLINA TERRANE, NORTH CAROLINA

Ediacaran to earliest Paleozoic mixed magmatic and sedimentary assemblages in the Carolina terrane include epiclastic to tuffaceous sequences in the Tillery Formation. The terrane was deformed primarily during the Late Ordovician Cherokee orogeny, that reached greenschist facies metamorphism in the central Piedmont of NC. East of the Pee Dee River, regional inclined to overturned folds with axial planar cleavage verge southeast. Mesoscopic sympathetic folds are attenuated or truncated by ductile shear zones or contractional faults. Shear and fault zones are most abundant near highly silicified stratiform zones; these zones are also auriferous. Ground penetrating radar profiles were collected across Tillery Formation mudstones and silicified, gold-bearing zones near the historic Russell gold mine. Several GSSI SIR-3000/100 MHz GPR profiles were collected in 2D profiles as much as 260 m long. In lines processed for background removal, clusters of shallow, sigmoidal reflectors are separated by sets of parallel, northwest-dipping reflective discontinuities. In the upper 5 m of these profiles, upwardly convex reflections are interpreted to be the culminations of asymmetric folds of bedding with vergence to the southeast. Planar northwest dipping reflections may be reverse faults that stack stratigraphy, or they may indicate the long limbs of overturned folds. After migration tests with velocities of 0.035-0.105 m/ns, vertical heights of the inferred folds become attenuated but not removed, and contractional fault reflections remain prominent. A 200 MHz 3D grid of approximately 1,200 square meters produced time slices containing high amplitude reflections from what are interpreted to be antiform culminations that trend northeast and that are parallel to trends of regional folds. Combined with surface structure, the GPR data suggest that the characteristic structural style in this area is populated by asymmetric folds in multiple wavelengths, all verging southeast. A strong axial planar cleavage transects bedding in hinges of these folds. Some reports indicate that quartz veins and ore horizons follow this strong cleavage, but some outcrops show siliceous zones folded along with bedding. This suggests that the ore horizons could be locally repeated by shallow plunging, inclined to overturned folds.