Preliminary geologic map of the Great Smoky Mountains National Park within the Fontana Dam and Tuskeegee quadrangles, Swain County, North Carolina

Southworth, Scott

The geology of the Great Smoky Mountains National Park (GSMNP) portion of the Fontana Dam and Tuskeegee quadrangles was mapped in 1993 and 1994 under a cooperative agreement between the National Park Service (NFS), National Biological Service (NBS), and the U.S. Geological Survey (USGS). Approximately 27 days were spent mapping in the months of May, June, and October; approximately nine days were spent mapping the north shore of Fontana Lake in November, 1993, when more than 60 vertical feet of steep exposure was provided by seasonal drawn down for flood control. Keith (1907) first mapped the geology of the area at 1:125,000-scale and part of the area was mapped in 1943 by Espenshade (1963) at l:24,000-scale. Portland P. Fox mapped the geology of the Fontana Lake region in 1944; this unpublished Tennessee Valley Authority (TVA) map is on file with the North Carolina Geological Survey in Asheville (L.S. Wiener, 1995, written comm.). The creation of Fontana Lake in 1944 by the TVA made the area inaccessible for the 1946 to 1954 USGS mapping project (King, 1964; King and others, 1968). Subsequent regional geologic maps at l:250,000-scale contain this map area (Hadley and Nelson, 1971; Robinson and others, 1992; Wiener and Merschat, 1992). Some of the most detailed work performed in the region is by Mohr (1972; 1975) in the adjacent (east) Noland Creek quadrangle. The Fontana Dam and Tuskeegee quadrangles are predominantly underlain by metamorphosed clastic sedimentary rocks of the Ocoee Supergroup (fig. 1). The rocks bear no known fossils and are interpreted to be Late Proterozoic in age. Late Proterozoic, as presently used, ranges from 1000 Million years ago (Ma) to the base of the Cambrian (Plumb, 1991), which is considered to be approximately 545 Ma (Bowring and others, 1993; Landing, 1994). The clastic rocks are dominantly metasandstone, metagraywacke, and metaconglomerate, with lesser graphitic metasiltstone and quartz-muscovite schist. The rocks are interpreted to be turbidites deposited in a deep-water basin (King and others, 1968) during continental rifting. They were presumably derived from the weathering of Middle Proterozoic granitic gneiss similar to that exposed to the east at Bryson City (King and others, 1968). The metasedimentary rocks contain minor bodies of mafic and felsic igneous rocks and vein quartz. Mafic metaigneous rocks include porphyritic metadiabase and fine-grained greenstone that are interpreted to have been intrusive dikes. Minor metamorphosed felsic pyroclastic volcanic rocks interpreted to represent explosion breccia are spatially associated with the greenstone. The mafic and felsic metaigneous rocks are the first recognized evidence of bimodal volcanism associated with Late Proterozoic continental rifting during Ocoee sedimentation in this region (Rankin and others, 1989). Carbonate-chlorite schist and vein quartz are interpreted to be related to deformation and metamorphic alteration in shear zones near the metaigneous rocks. The massive sulfide deposits of the Fontana Copper mine, as discussed in a later section, are spatially associated with and interpreted to be genetically related to the igneous rocks within the Eagle Creek shear zone.

Preliminary geologic map of the Great Smoky Mountains National Park within the Fontana Dam and Tuskeegee quadrangles, Swain County, North Carolina

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