KINEMATICS AND TIMING OF THE GOLD HILL SHEAR ZONE, SOUTH-CENTRAL NORTH CAROLINA: IMPLICATIONS FOR SINISTRAL TRANSPRESSION IN THE SOUTHERN APPALACHIANS

The Gold Hill shear zone (GHsz) is a first-order structure in the Carolina Zone (CZ) of the southern Appalachians that separates medium-grade, ductiley deformed rocks of the Charlotte terrane (Cht) from low-grade, mildly deformed rocks of the Carolina terrane (Ct). Based on circumstantial evidence, the GHsz has traditionally been viewed as an Acadian dextral shear zone. However, at the western boundary of the Ct, Late Ordovician, NE trending, en echelon regional folds are truncated by the NNE trending GHsz. The orientation of these folds relative to the trace of the GHsz suggests previously undocumented early sinistral shear along this major structure.

At the western boundary of the Ct in the vicinity of High Rock Lake, North Carolina, rocks of the Albemarle Group (AG) are folded about the SW plunging axis of the Silver Valley syncline (SVs) and imprinted by a steep NE striking axial planar cleavage. In this area, the GHsz truncates structures associated with the SVs and consists of two distinct structural domains. The southern domain is characterized by AG units deformed by upright, SW trending, outcrop-scale folds that contain a steep, NNE to NE striking axial planar cleavage. The folds and cleavage in this domain are similar in geometry and style to the SVs and are interpreted to be genetically related to regional folds in the CT. The northern domain consists of phyllite, chlorite schist, and felsic meta-volcanic rock of uncertain vintage. Foliation surfaces in this domain, which strike NNE and dip steeply, contain a consistent down-dip stretching lineation, as well as a heterogeneously distributed subhorizontal stretching lineation. Asymmetric foliations indicate that motion on the GHsz involved thrusting of the Cht over the Ct coupled with sinistral strike-slip motion. These new structural and kinematic relationships suggest Late Ordovician or younger sinistral transpression that may be related to the accretion of the CZ to Laurentia. 40Ar/39Ar dating of white mica associated with the shear zone fabrics and U-Pb zircon dating of magmatic rocks related to the shear zone is currently in progress in order to constrain the timing of movement along this significant structure in the southern Appalachians.