NEW AEROMAGNETIC SURVEY ACROSS PART OF THE SOUTHERN APPALACHIANS, TENNESSEE AND NORTH CAROLINA

The U.S. Geological Survey contracted a new fixed-wing aeromagnetic survey of part of the Southern Appalachians in 2003. The aim of the survey was to fill in the gaps of the aeromagnetic coverage of flight line data spaced 1-mile or less in Tennessee and North Carolina, and to provide a tool for bedrock geologic mapping. The survey is in 3 parts, a long rectangle from –84.5^o to –81.75^o longitude between 35.5^o and 36^o latitude, and two smaller triangular areas on the north and south edges. Flight line spacing is 500 m in the major block and 1 km in the two smaller areas. The survey spans some of the highest peaks and the most rugged terrain in eastern North America, and it includes the northern part of the Great Smoky Mountains National Park, and the cities Knoxville, TN and Asheville, NC.

The broad, large-amplitude (1100 nT) anomaly near Knoxville probably has its source in Mesoproterozoic basement beneath Valley and Ridge Paleozoic cover rocks; the eastern gradient is a segment of the New York-Alabama magnetic lineament. The magnetic field indicates a nearly uniform, very low magnetization for the western Blue Ridge metasedimentary rocks of the Ocoee Supergroup, except for parts of the Anakeesta Formation, which is marked by low-amplitude anomalies, the most prominent being at Thunderhead Mountain. Short wavelength positive magnetic anomalies in the central-eastern Blue Ridge are linked with part of the exposed Mesoproterozoic basement rock. Some of these anomalies may trace basement rocks beneath the overlying Tallulah Falls-Ashe Formation thrust sheet. Anomalies of similar shape and amplitude occur southeast of Asheville and raise the possibility of basement there. A broad magnetic high at Mt Mitchell may be the expression of deep basement. The Western Inner Piedmont is characterized by many narrow, northeast-trending, linear magnetic anomalies. The Henderson Gneiss may be a source for the largest of these anomalies. In westernmost North Carolina, linear magnetic anomalies are correlated with rocks of the Murphy synclinorium, especially the Mineral Bluff Formation and parallel units in the Great Smoky Group.