Structure and Kinematics of the Gold Hill fault zone in the vicinity of Waxhaw, North Carolina

Abstract

The Gold Hill fault zone is a first-order structure within the peri-Gondwanan Carolina zone that separates Neoproterozoic metavolcanic rocks of the Charlotte and Carolina terranes. Previous work suggests that a north-south trending ductile shear zone, the Davis Branch shear zone, merges with the Gold Hill fault zone (s.s.) in the vicinity of Waxhaw, North Carolina. This region of the Carolina zone was chosen to investigate the relationship between the Davis Branch shear zone and the Gold Hill fault zone, and to delineate the structural relationship between the Gold Hill fault zone and surrounding volcaniclastic terranes. The results of this study may shed new light on the tectonic history of the southern Appalachian Carolina zone.

Geologic mapping identified low-grade volcanic sequences on each side of the Gold Hill fault zone. Northwest of the Gold Hill fault zone lies the Marvin sequence, which is composed of dacitic quartz tuffs, porphyries, and minor amounts of mafic-derived sedimentary rock and schist. Southeast of the Gold Hill fault zone lies the Twelve Mile sequence, which consists of a suite of rhyolitic volcaniclastic lapilli and lithic tuffs and an overlying sedimentary package of fine-grained siliciclastic sediments and minor conglomerate. Deformed rocks in the Twelve Mile sequence make up the bulk of the Gold Hill fault zone. Intruding the Twelve Mile sequence is granitic Waxhaw pluton that has thermally metamorphosed portions of the volcanic sequence.

Both the Marvin and Twelve Mile sequences exhibit geologic features that are similar to the other volcaniclastic sequences in the Carolina terrane. These observations question early interpretations that the Gold Hill fault zone represents a terrane boundary between the Carolina and Charlotte terranes. Moreover, detailed geologic mapping and strain analysis also indicate the Davis Branch shear zone, originally reported as a north-south trending ductile shear zone, is not present within the Waxhaw, NC study area.

Structural analysis of the Gold Hill fault zone suggests it is a steeply dipping zone of dextral wrench-dominated transpression defined by a wide footwall damage zone in the Twelve Mile sequence and narrow hanging wall damage zone in the Marvin sequence. Structures within the Gold Hill fault zone are attributed to deformation along the Gold Hill fault, which is a right lateral reverse fault with southeast vergence that thrusts the Marvin sequence over the Twelve Mile sequence. Strata in both volcanic sequences are folded into upright, northeast-plunging, folds imprinted by a steeply dipping axial planar cleavage that strikes sub-parallel to the trace of the Gold Hill fault zone. Metamorphic and microtextural data suggests that the Waxhaw granite, which intrudes the Twelve Mile seqeucne, is synkinematic to deformation within the fault zone, and support the interpretation that Gold Hill fault thrusts the Marvin sequence over the Twelve Mile sequence.