AN EXTENSIVE TWO-PYROXENE DIABASE DIKE IN THE EASTERN PIEDMONT OF NORTH CAROLINA

A coarse-grained, two-pyroxene, granophyre- and locally olivine-bearing diabase dike has been mapped and studied in the eastern Piedmont of North Carolina. This dike is texturally and mineralogically distinct from the common olivine diabase dikes of the region. It has been mapped, primarily in the course of STATEMAP quadrangle mapping, from central Johnston County to the Virginia border, a distance of about 120 km. It may be an extension of the Farmville, VA dike described by Dudás and Rogan (1999), and if so its strike length may exceed 250 km. In the southern part of its outcrop area near Flowers, North Carolina, the dike trends about N15°W, curving to a N-S direction near Rolesville, and then to approximately N10°E north of Henderson. Where we have mapped it, the dike appears to be between 32 and 40 meters in width; field evidence and magnetic modeling suggests that it dips eastward 75-80° near Middleburg. Where we have mapped it, the dike intrudes granitoid country rocks of the late Paleozoic Rolesville batholith and older metamorphic rocks of the Spring Hope and Raleigh terranes. The dike also intrudes rocks that have been ductilely deformed within the late Paleozoic Nutbush Creek fault zone, but the diabase shows no evidence of ductile deformation. In several places, the dike is transected by brittle faults at a high angle, and in at least one location the dike is clearly cut and offset along a north-dipping normal fault. In the only outcrop we have found exposing the dike's contact, a chill zone is present; away from the contact the diabase is unusually coarse grained, with plagioclase up to two cm. Changes in texture and modal mineralogy across the dike in several places suggest the possibility of crystal fractionation or some other magmatic process(es) during intrusion and crystallization of the dike. Field mapping and laboratory work, including whole-rock and mineral analyses, are underway in order to document the dike and model its evolution.