FOLD KINEMATICS IN A PERICLINAL ANTICLINE, CAROLINA TERRANE, NORTH CAROLINA

The Neoproterozoic to Cambrian Albemarle arc accreted to the eastern margin of Laurentia during the Late Ordovician to Early Silurian Cherokee orogeny as part of the Carolina terrane. In North Carolina, the arc infrastructure deformed under greenschist facies into fold groups with wavelengths of tens of kilometers that trend northeast-southwest and verge southeast. Some folds are doubly-plunging adjacent to the multiphase Gold Hill shear zone (GHsz). They are interpreted as transpressional structures.

We have investigated fold relationships in a periclinal antiform (wavelength ~ 5 km) between the New London synclinorium and Uwharrie anticlinorium in the footwall of the GHsz by mapping turbidites and rhyolite in the Cambrian Tillery Formation. Slaty cleavage in argillites is continuous and axial planar to crenulations at rheological boundaries like base layers in turbidite cycles. The cleavage is represented by dimensional alignment of equilibrated quartz grains in siltstone layers. Crenulations mimic the geometry of lower order folds within the pericline.

Argillites are phyllitic near rhyolite contacts because of mechanical contrasts and/or mobilization of silica during folding and metamorphism. Anastomosing, spaced cleavage is strong within rhyolite near the contacts. In turbidite siltstones, axial planar cleavage is domainal and contains quartz or calcite veins in extensional zones within those stiffer layers. Near sedimentary-volcanic layer boundaries a syngenetic silicified and locally gold-bearing zone contains folded and altered argillite, pre-tectonic quartz veins, thin altered rhyolite lenses, and hydrothermal minerals.

Kinematically, higher order folds are congruent with horizontal shortening by folding during accretion of the Carolina terrane. Microfaults in bedding are common but no larger faults are documented within the study area. Axial planar cleavage morphology is consistent with layer boundary contrasts down to the microscopic scale. We have also documented post-collisional kink bands, some with axial microfaults or veins, that trend northerly. Deviations in site-wide axial planar cleavage and bedding attitudes weakly reflect rotation by this late phase folding. The kinks are likely connected to Late Devonian or Mississippian deformation of the terrane.