NEW GEOLOGIC MAPPING AND RESEARCH IN THE GEORGE WASHINGTON, JEFFERSON, CHEROKEE AND PISGAH NATIONAL FORESTS, APPALACHIAN BLUE RIDGE, VA-NC-TN

The USGS is conducting geologic mapping and research in eastern National Forests (NF) through the Appalachian Blue Ridge Project. Blue Ridge (BR) geology under investigation includes Mesoproterozoic metagranitoids, newly recognized Early Neoproterozoic paragneisses, Late Neoproterozoic sedimentary and volcanic rocks, and Early Cambrian clastic sedimentary rocks of the Laurentian passive margin. Multiple collisional and extensional orogenies are recorded by the BR during the Mesoproterozoic, Early Neoproterozoic, and middle to late Paleozoic. The study area crosses the eastern continental divide, where Miocene uplift and stream capture preserves the enigmatic Blue Ridge Plateau and escarpment. Pleistocene debris fans and colluvium are abundant in the uplands while Pliocene-Pleistocene alluvial fans mantle the west margin.

Along a 2-mile-wide corridor centered on the 218 mile-long Blue Ridge Parkway in VA, we are expanding our studies into the George Washington and Jefferson NF’s (north and south of the James River, respectively). Detailed geologic mapping separates Mesoproterozic granitoids and re-defines the stratigraphy of the Neoproterozoic and Cambrian strata. U-Pb SHRIMP analyses of Mesoproterozoic rocks have yielded one of the oldest (~1.2 Ga) and the youngest (1.0 Ga) metagranitoids of the Shenandoah massif.

Our study within the Mount Rogers National Recreation Area is within the Jefferson NF of southern VA and part of the Cherokee NF of TN and examines the Mesoproterozoic history of the French Broad massif which includes the oldest BR meta-igneous rock (1.32 Ga), the overlying sedimentary and bi-modal volcanic rocks of the ~760 Ma Mount Rogers Formation and the glaciogenic sediments of the Konnarock Formation, and the unconformably overlying Cambrian Unicoi Formation.

Detailed geologic mapping in the Roan Mountain area is within the Pisgah NF, NC-TN is separating felsic and mafic granulite gneisses and metagabbro dikes. The reported 1.8 Ga paragneisses are reinterpreted to be deposited after 900 Ma, and metamorphosed at granulite-facies, prior to intrusion of ~760 Ma metagabbro dikes, likely correlative with Mount Rogers igneous activity. Important geologic rocks and field relationships in NF lands continue to provide new insight to Appalachian geology.