STRATIGRAPHY AND STRUCTURE OF THE EASTERN BLUE RIDGE: VIRGINIA AND NORTH CAROLINA

Recent detailed mapping along the Blue Ridge Parkway and vicinity in southern VA and NW NC provided the opportunity to evaluate existing stratigraphic and structural models, and formulate new ideas for regional correlations of EBR geology.

Recent mapping demonstrates that Lynchburg Group (LG) rocks in central VA – metagraywacke, quartzite, graphitic schist, and mafic-ultramafic rocks – continue southwestward along strike and transition into the Wills Ridge (WRF), Ashe (AF) and Alligator Back (ABF) formations. The structurally lowest WRF consists of graphitic schist, metagraywacke, and metaconglomerate. Along the Parkway in southern VA, the AF consists of K-feldspar-bearing metaconglomerate; in NW NC mica gneiss and schist, and mafic-ultramafic rocks comprise the AF. Overlying rocks of the ABF show characteristic compositional pin-striped layers in mica gneiss, schist and amphibolite, and contain trace tourmaline.

The contact between Mesoproterozoic basement and overlying EBR stratified rocks is considered to be a fault (Gossan Lead and Red Valley). The cryptic Callaway fault juxtaposes AF and LG rocks above WRF, but more recognizable faults to the SE break the EBR into distinct belts differing in lithology, deformation and metamorphism. ABF rocks overlie AF and LG rocks along the syn- to post-metamorphic Rock Castle Creek fault system (RCCF), which juxtaposes rocks of different metamorphic grades. The RCCF separates major structural domains: bedded siliciclastic rocks of the LG and AF with one penetrative foliation and abundant ultramafic rock bodies occur in the footwall, and compositional layering, superposed penetrative foliations and cleavage characterize ABF rocks in the hanging wall. RCCF kinematic indicators (mineral lineations and fold axes) in southern VA are mostly top-to-NW; tectonic stacking along the RCCF inverted the regional metamorphic gradient. These structural relationships are unresolved to the SW in NW NC where AF and ABF rocks are recrystallized at higher metamorphic grades.