STRATIGRAPHIC RELATIONSHIPS IN THE MURPHY BELT OF NORTH GEORGIA AND WESTERN NORTH CAROLINA AND THEIR IMPLICATIONS FOR THE TECTONIC DEVELOPMENT OF THE WESTERN BLUE RIDGE, SOUTHERN APPALACHIANS

Metasedimentary units and related metaigneous rocks in the Murphy belt of N. Georgia and W. North Carolina comprise three distinct sequences that document, in part, the tectonic history of the western Blue Ridge (WBR) in the Southern Appalachian. These sequences include (from oldest to youngest): 1) Rocks of the Ocoee Supergroup (OS), an immature meta-clastic sequence deposited along the rifted edge of the ancient North American Continent. 2) The Hiwassee River Group (HRG), a mature metasedimentary package including continental shelf facies siliciclastics and a carbonate bank sequence. 3) The Mineral Bluff Group (MBG), a diverse clastic sequence that includes metamorphosed olistostromes, metaconglomerates, metasandstones, metapelites, and interbedded metavolcanic units that record the post-drift history in the western Blue Ridge. A single crinoid stem recovered from the lower MBG indicates that the MBG is post-Cambrian. Well-documented exposures of 1.1 b.y. Greenville basement (GB) rocks occur in the WBR and underlie the younger metasedimentary cover units. These GB units in concert with other correlations support links between the WBR and Laurentia. The OS rests nonconformably on older Greenville-age rocks. The OS-HRG contact has been studied by a number of workers, most of whom interpret it to be a gradational contact. The MBG is underlain by an unconformity. The pre-MBG unconformity places the younger MBG sequence in contact with older rocks of the HRG and OS. Mafic metavolcanic units in the MBG, along with the diverse coarse clastics in the MBG, indicate that a significant change in tectonic environment, specifically a change from passive continental margin to active continental margin, must have occurred sometime prior to the deposition of the MBG rocks. Additionally, correlations between rocks of the MBG and rocks of the Talladega Group in the Talladega belt to the southwest indicate a middle or late Paleozoic metamorphic event in the WBR. This interpretation is supported by recent radiometric dating studies. These findings contribute greatly to our understanding of the middle to late Paleozoic history of the WBR.