GEOLOGIC MAP OF THE SOUTHWESTERNMOST SECTION OF THE BLUE RIDGE PARKWAY IN VIRGINIA: MEADOWS OF DAN, PATRICK COUNTY, VA TO CUMBERLAND KNOB, SURRY COUNTY, NC

Detailed geologic mapping on seven 7.5-minute quadrangles within a 2-mile wide corridor centered on the Blue Ridge Parkway concludes a 4-year project that links with detailed mapping along the NC portion of the Parkway by the North Carolina Geological Survey. The completed map of the 469 mi Blue Ridge Parkway links the existing geologic maps of the Shenandoah National Park and Great Smoky Mountains National Park, providing a unique geologic transect of the Blue Ridge.

Rocks along this section of the Parkway consist mostly of Alligator Back Formation (ABF), comprised of a sequence of biotite-muscovite gneiss, schist and amphibolite (with minor ultramafic rock, and rare graphitic schist and marble). These eastern Blue Ridge strata are in the core of the Ararat River synclinorium and are considered to be late Neoproterozoic to early Paleozoic in age. The gneiss and amphibolite have distinctive pin-striped foliation, consisting of 1- to 5-mm thick alternating layers of quartz-feldspar and phyllosilicate (biotite-muscovite gneiss), or quartz-feldspar and chlorite-biotite-amphibole (amphibolite). Schist characteristically contains porphyroblastic garnet (and locally staurolite) as much as several cm in diameter, in a matrix of chlorite-biotite-muscovite.

ABF rocks are distinguished from structurally lower rocks to the west; ABF contains little graphitic schist, few ultramafic rocks, and rare marble, and is polydeformed and likely polymetamorphosed. The ABF occurs above rocks assigned to the Ashe Formation (AF) and Lynchburg Group (LG), but the contact is faulted and syn- to post-metamorphic. ~3.8 km north of Meadows of Dan, top-to-NW thrust faults (Rock Castle Creek fault system) juxtaposed staurolite-grade ABF rocks on garnet-grade AF-LG rocks, but ~1.4 km NW of Fancy Gap, mineral lineations support a component of sinistral motion along the contact, with lower grade ABF rocks juxtaposed against higher-grade rocks to the west.