STRATIGRAPHIC AND STRUCTURAL SETTING OF BASEMENT MASSIFS IN THE BLUE RIDGE OF NORTH GEORGIA

Numerous allochthonous Grenvillian (~1.1 Ga) basement massifs in the Appalachian orogen occur in fault juxtaposition with Paleozoic rocks along the southeastern margin of the foreland from Newfoundland to Georgia. In the central and southern Appalachians, these external basement massifs occur as anticlinorial culminations within the western Blue Ridge that have been detached with their metamorphosed and polydeformed cover rocks and thrust large distances north westward above adjacent rocks of the foreland during latest Paleozoic thrusting. The three southernmost external massifs in the orogen (Corbin, Salem Church, and Fort Mountain) occur in north Georgia within the cores of a series of northwest-verging, steeply inclined to recumbant, isoclinal anticlines, immediately above the frontal thrust of the western Blue Ridge. These basement-cored anticlines, formed under greenschist facies conditions, were later detached and thrust northwest across a Lower Cambrian Rome Formation footwall flat in the immediately adjacent foreland. The dominantly metaplutonic basement rocks are overlain directly by two rift facies cover sequences of late Proterozoic age (Snowbird and Great Smoky Groups) that represent two distinct stages of rift basin evolution. The older sequence (Snowbird Group) rests nonconformably on basement and consists of shallow-water arkosic metasandstone and metawacke, and minor metapelite. The younger sequence (Great Smoky Group) consists of deeper water, metadiamictite, metaturbidite, metawacke, and metapelite, and lies unconformably upon the first, locally cutting entirely through it to also rest nonconformably upon basement. Regional distribution of the two sequences suggests that they were separated in time by a period of significant extensional (rift-related), down-to-the-southeast, faulting. One of these major pre-metamorphic faults is now located in the core of the Fort Mountain anticline, where it is cut by the unconformity at the base of the Great Smoky Group. Northwest of the trace of this fault, Snowbird Group rocks are absent.