GEOLOGY OF THE VICKSBORO QUADRANGLE, NC: IMPLICATIONS FOR EASTERN PIEDMONT PLUTONS, FAULT ZONES, AND TERRANES

Granitic plutons in the eastern NC Piedmont along the US Highway 1 corridor are dissected or sandwiched by and intruded along dextral fault zones of the Eastern Piedmont fault system (EPFS). In the Middleburg 1:24K Quadrangle, a swath of variably deformed granitic rocks lies between two high-strain strands of the EPFS - the Nutbush Creek fault zone (NCFZ) on the west, and the Lake Gordon fault zone (LGFZ) on the east. The greenschist-facies suprastructural Carolina terrane, with Neoproterozoic to Cambrian magmatic and volcanogenic sedimentary rocks, sits west of the NCFZ. Amphibolite-facies infrastructural metaigneous and metasedimentary rocks lie east of the LGFZ and have been assigned to the Raleigh terrane.

During the past 30 years, the Rolesville granite batholith has been mapped northward, quadrangle by quadrangle, through Franklin and Vance Counties, under the National Cooperative Geologic Mapping Program. The Vicksboro Quadrangle (VQ) lies between the Middleburg and Ingleside Quadrangles and constitutes the sole remaining gap. We have identified several distinct granitoid facies, using the approach Speer (1994) applied in the Raleigh 1:100K sheet, by differences in textures, mineral assemblages, enclaves, and overprinting fabric elements. These granitoid facies likely are nested plutons.

The NCFZ passes through the Henderson Quadrangle, west of the VQ, and overprints granitoid rocks south of the syntectonic Buggs Island pluton in the Henderson 1:100K sheet. New mapping indicates that undeformed Rolesville batholith granite in the south-central portion of the VQ truncates LGFZ mylonitic ortho- and paragneiss, implying that at least some granite post-dates dextral slip along the LGFZ. The western, sheared portion of the Rolesville batholith may be a southward extension of the Buggs Island pluton. Regionally, strands of the EPFS appear to serve as deep conduits for intrusion of mid-crustal melts. Most plutons are inferred to be Pennsylvanian-Permian in age. However, recent Petersburg granite data in VA indicate some foliated facies are Early Devonian plutons (Carter et al., 2019). These data may indicate that some eastern NC Piedmont plutons are of a similar age, especially given the recent reports of Early Devonian magmatic ages from the Raleigh terrane (Peach et al., 2017; Finnerty et al., 2019).