Preliminary geologic map of the Lunenburg and Fort Mitchell 7.5' quadrangles, Virginia

Abstract

The Lunenburg and Fort Mitchell 7.5' quadrangles have been mapped as part of the Geology of the South-Central Virginia Piedmont Project, a regional geologic mapping project of the U.S. Geological Survey. The two quadrangles include parts of Lunenburg, Mecklenburg, and Charlotte counties, and are located in the east-central part of the South Boston 30'x60' quadrangle (Figure 1). A preliminary geologic map of this quadrangle has been published (Norton and others, 1993), and a reconnaissance map by Laney (1917) includes the western Fort Mitchell quadrangle. Aeromagnetic and aeroradioactivity maps that include the field area have been published by the U.S. Geological Survey (1978a, 1978b). The Lunenburg and Fort Mitchell quadrangles are adjacent to the north and northwest, respectively, to the previously mapped Wightman 7.5' quadrangle (Burton, 1993; Figure 1). With respect to geologic provinces, the Lunenburg and Fort Mitchell quadrangles are located within the Carolina slate belt of the Carolina Terrane (Figure 1) and have not been previously mapped in detail. The Carolina slate belt in this area consists of volcanic and sedimentary rocks and associated intrusive igneous rocks that possess a regional slatey cleavage and have been subjected to lower greenschistfacies metamorphism. An earlier, pre-cleavage deformation and low-grade metamorphism may have occurred in the Late Proterozoic (Glover and Sinha, 1973). The rocks are locally poorly dated but probably are Late Proterozoic and Early Cambrian in age (Butler and Secor, 1991, and references therein). The Carolina slate belt may represent a subduction-related volcanic arc (Butler and Secor, 1991), or riftedarc complex (Feiss and others, 1993). Geochemical analysis and radioisotopic dating (U-Pb and 40 Ar/ 39 Ar) of slate belt rocks in the South Boston 30 x 60' quadrangle by the U.S.G.S. are in progress.