27 Structural Geology, Metamorphism, and Geochronology of the Southern Appalachian Blue Ridge

Friday, 30 March 2007
8:00 AM - 12:20 PM

DETAILED GEOLOGIC MAPPING OF THE CENTRAL AND EASTERN BLUE RIDGE CONTACT IN THE GREAT BALSAM MOUNTAINS, WESTERN NORTH CAROLINA

Paper number: 27-2
Program: THEME SESSIONS
Time: 8:20 AM – 8:40 AM

Authors

Abstract

Detailed geologic mapping of the Waynesville and Sam Knob 7.5-minute quadrangles (~340 km2) in the central and eastern Blue Ridge of western North Carolina recognizes the Dahlonega gold belt (DGB), Cartoogechayee (CRT), and Tugaloo (TG) terranes exposed as three separate thrust sheets framing the Great Balsam Mountains window (GBMW). The lowest thrust sheet (DGB) exposed in the GBMW extends from near Sylva to Canton, NC, with several smaller windows along its NW flank. Sillimanite-biotite -muscovite schist and metagraywacke, correlated with DGB Otto Formation dominate. Rare mafic and ultramafic rocks occur as small lenticular bodies. The Soque River-Hayesville fault transported migmatitic rocks of the CRT above the DGB. CRT rocks are pervasively migmatitic, and include amphibolite, felsic gneiss (Grenville basement?), and dominant biotite gneiss. No ultramafic rocks were observed here, despite common occurrences throughout the CRT. The TG, the highest thrust sheet juxtaposes Tallulah Falls Formation (TF) against DGB rocks, and CRT further to the NE and SW by the Chattahoochee-Holland Mountain fault. TF rocks are migmatitic and consist of lower metagraywacke and amphibolite and upper metagraywacke and schist members separated by aluminous schist. Magnetite-bearing muscovite schist unit and magnetite-bearing muscovite-biotite granitoid occur in the upper member.

Foliations preserved in amphibolite boudins represent the earliest deformation, D1. The dominant structures throughout the field area are D2, including penetrative S2 foliation defined by micas, sillimanite ± kyanite, hornblende, and migmatitic layering. S2 parallels the E-W trend and subvertical dip of the Soque River fault suggesting it is D2. SHRIMP U-Pb detrital zircon rim ages of ~455 Ma from the GBMW, and published monazite and zircon rim ages from the surrounding terranes suggest D2 is Taconic. D3 is characterized by a weak S3, E-W trending crenulations, and upright-to-inclined, tight-to-open E-W trending F3 folds. Upright NNE to E-W folds superposed on the Soque River fault are interpreted as F3. The Chattahoochee fault juxtaposes rocks of similar grade, is folded isoclinally, and oriented parallel to S2 suggesting a Taconic age. Along-strike truncation of the ~335 Ma Rabun Granodiorite indicates the fault is Mississippian.