LITHODEMIC AND TECTONOTHERMAL CHARACTERIZATION OF THE RALEIGH TERRANE IN THE MIDDLEBURG AND JOHN H. KERR DAM 7.5-MINUTE QUADRANGLES, NORTHEASTERN NORTH CAROLINA PIEDMONT

In the northeastern North Carolina Piedmont, the northern Raleigh terrane exposed within the Middleburg and John H. Kerr Dam 7.5-minute quadrangles contains garnet-sillimanite zone metamorphism that overprints mixed igneous and sedimentary protoliths. The Raleigh terrane may be part of the peri-Gondwanan Carolina Zone, an amalgamation of Late Proterozoic to early Paleozoic island arc terranes accreted to Laurentia and now exposed along the eastern flank of the southern Appalachian orogen. Alternatively, the Raleigh terrane may be a southern extension of the Goochland Zone of Virginia, the easternmost exposure of Grenville-age rocks in the orogen. As part of the NCGS STATEMAP mapping project in the Henderson 30x60-minute quadrangle, this study evaluates the correlation between rocks of the northern and southern Raleigh terrane currently considered to be separated by the Rolesville batholith.

This study focused on tectonothermal relationships in the Raleigh terrane between the Nutbush Creek and Lake Gordon fault zones. These two fundamental Alleghanian ductile dextral strands of the Eastern Piedmont fault system are exposed along the eastern and western boundaries of the two quadrangles. From west to east, mapped units include the Vance County pluton of the Carolina terrane, Alleghanian granitoids, and a suite of schist and gneiss. The western rocks exhibit ductile deformation related to Nutbush Creek displacement, including dextral porphyroclasts and mica fish, S-C foliation, C' shear bands, thrust faults, and fold vergence. Mylonitic gneiss east of the deformed Vance County pluton is granitoid melt injection correlated with the emplacement of the Alleghanian Buggs Island pluton. However, east of the mylonitic granitoid gneiss, garnet-sillimanite schist and fine-grained biotite gneiss lying within and east of the Lake Gordon fault zone may have sedimentary protoliths. Metasedimentary bulk compositions and mineral assemblages are not observed around Raleigh, the type locality of the Raleigh terrane. The Lake Gordon fault zone and Alleghanian plutons separate northern Raleigh terrane metasedimentary rocks and mineral assemblages from southern Raleigh terrane metaigneous rocks. As a consequence, all rocks currently grouped as “Raleigh terrane” may actually be two separate tectonic entities.