REGIONAL AND CONTACT METAMORPHISM OF TALLULAH FALLS FORMATION CALC-SILICATES IN THE EASTERN BLUE RIDGE OF SW NORTH CAROLINA, NE GEORGIA, AND NW SOUTH CAROLINA: CAN THEY HELP US BETTER UNDERSTAND THE METAMORPHIC EVOLUTION OF THE SOUTHERN APPALACHIANS?

Calc-silicate rocks in the eastern Blue Ridge of SW North Carolina, NE Georgia, and NW South Carolina are the product of contact and regional metamorphism. Contact metamorphosed calc-silicate xenoliths (Type A) occur in the ~336 Ma Rabun Granodiorite batholith. The batholith is bound to the west by the Alleghanian Chattahoochee-Holland Mountain thrust fault; to the east is the Tugaloo terrane, which exhibits decreasing Barrovian metamorphic grade from west to east toward the Brevard fault zone. Type B calc-silicates occur as mappable thin, elongate, ribbon-like units. Petrographic and geochemical data confirm a similar composition for both types and a mineral assemblage that includes epidote, amphibole, garnet, diopside, quartz, and plagioclase with accessory zircon, sphene, and opaque minerals. Calcite, however, is only present in Type A xenoliths. Despite similar compositions, they have markedly contrasting textures: Type A calc-silicates are megacrystic and well-foliated, while the Type B calc-silicates are weakly to non-foliated and have a glassy, quartzitic appearance. Neoacadian regional metamorphism and deformation initially formed the calc-silicates from an impure dolomite protolith. Contact metamorphism plus fluids produced the megacrystic grain size, calcite, and reaction textures in Type A xenoliths during Alleghanian emplacement of the Rabun Granodiorite. Understanding the polymetamorphic evolution of these rocks has provided more insight into the tectonic history of the southern Appalachians.