PETROFABRIC ANALYSIS OF THE GREAT SMOKY-SNOWBIRD GP. CONTACT, COVE CREEK AREA, EASTERN GREAT SMOKY MTNS., NC

The nature of the contact between the Great Smoky and Snowbird Gps. has long posed a problem for interpretation of the tectonic evolution of the southern Appalachian Blue Ridge. The contact has been interpreted as a premetamorphic fault, lithologic contact, or a faulted contact. High-grade Taconian (?) regional metamorphism and folding, and post-metamorphic (Alleghanian?) deformation complicate interpretation. Structural and petrofabric analysis of the contact provide first order constraints on the deformation history and models for assembly of the present architecture of the Great Smoky Mountain region. Detailed traverses across and along the Great Smoky-Longarm Quartzite (GS-LQ) contact were made near Cove Creek, north of Maggie, NC. The contact is tightly to isoclinally folded with S0 trending ~NE. S1 is defined macroscopically as schistosity in GSG. Individual layers of GSG and LQ are as thin as 10 cm. GSG contains Ky + Grt + Ms + Bt assemblages, consistent with regional isograds. However, GSG and LQ are mylonitic and display spectacular ductile microstructures that strongly overprint regional metamorphic assemblages and foliations. Microstructures in LQ include dynamic recrystallization of quartz, feldspar, biotite, and sphene, mica fish, and S/C fabrics; these and flattening of the foliation around Grt porphyroblasts, and extension/boudinage of kyanite porphyroblasts occur in the GSG. Sense of shear based on asymmetry of microstructures is mostly top-to-SE, but more samples are necessary before the significance of this asymmetry is determined. Retrograde breakdown of Grt is limited to Bt formation during shear. We cannot resolve any premetamorphic microstructures in either GSG or LQ; the contact appears to be lithologic. The microstructures could be related to the regional “slip cleavage” of Hadley and Goldsmith [’63]. Assuming Ky-grade metamorphism is Taconian, the fabrics imply a period of deformation along the contact during late Taconian or Alleghanian orogenesis.