LITHODEMIC AND STRUCTURAL ANALYSIS IN THE OXFORD 7.5-MINUTE QUADRANGLE, NORTHEASTERN PIEDMONT OF NORTH CAROLINA

The Oxford 7.5-minute Quadrangle is located in the northeastern Piedmont of North Carolina. It lies within the north-central portion of the Late Proterozoic to Cambrian Carolina Zone, a first-order tectonostratigraphic island-arc superterrane in the southern Appalachian orogen. Within the confines of the quadrangle, Carolina terrane metaigneous and metasedimentary rocks and clastic infill of the Durham basin, which defines the northern termination of the Deep River Triassic basin, are the focus of this study. Detailed geologic mapping as part of the NCGS STATEMAP project has delineated a number of new lithodemic units and basin bounding structures in the quadrangle.

Mapped units include greenschist facies equivalents of gabbro, diorite, quartz diorite, granodiorite, and granite lithodemes, as well as felsic pyroclastic and volcaniclastic rocks interpreted to be members of the Hyco and Aaron Formations of the 612-633 Ma Virgilina sequence. Silicified volcaniclatic rocks surrounding two topographic highs in the northwestern portion of the quadrangle are interpreted to be volcanic centers of the Hyco Formation creating two siliceous sinters. Mafic enclaves are common in metaplutonic rocks and one foliated enclave near these siliceous sinters in the northwestern portion of the quadrangle may represent Virgilina deformation. Geochemical analyses of metaplutonic rocks reveal markedly similar island-arc enrichment and depletion trends and tectonomagmatic origins as compared to metaigneous rocks of the Cary terrane to the south and Carolina terrane rocks to the west. These data strengthen the links among Carolina Zone terranes.

In the southern portion of the quadrangle, phyllonite and cataclasite of the informal Fishing Creek fault separate clastic rocks of the Durham basin from metaplutonic rocks of the Carolina terrane to the east. Ductile shear zones form an anatomizing structural grain along the entire east side of the quadrangle and as far east as the ductile dextral Alleghanian Nutbush Creek fault zone. Along the northern extent of the Fishing Creek fault 6 km north of the last outcrop of basin rocks, cataclasite and silicification progressively overprint phyllonitic and mylonitic plutons. Only local zones of cataclasite, foliation, and silicification mark the western edge of the Fishing Creek fault.