PETROLOGY, GEOCHEMISTRY, AND STRUCTURE OF TALLULAH FALLS FORMATION PARAGNEISSES, CORBIN MOUNTAIN (ZIRCONIA 7.5-MINUTE QUADRANGLE), GREENVILLE COUNTY, SC

Road cuts (650 m long) at Corbin Mountain, northern Greenville County, SC expose muscovite-biotite paragneiss, interlayered biotite schist, and migmatite of the Tallulah Falls Formation. The rocks are part of the Six Mile thrust sheet located within a fault block of the Gap Creek brittle fault zone. Most lithologies are mylonitic. Well-developed foliation and layering (general trend N50W 15NE) consist of alternating aligned micas and quartz-feldspar ribbons (2-5 mm thick). Nearly recumbent isoclines, tight folds, and ptygmatic folds verge west. Limbs of isoclines are sheared out locally along foliation surfaces. Intrafolial folds are present. Pre- and post-folding leucocratic granitic (pegmatitic-aplitic) dikes intrude the paragneiss; one set parallels the dominant foliation, is locally boudinaged, and has biotite selvedges, indicating a “sweat out origin” during metamorphism. Another set is discordant and planar with primary foliation parallel to dike margins. The third set is irregular in shape, discordant, and locally composite. Systematic joint sets are oriented N65W vertical, and N50E 80NW, and both are reactivated by essentially left strike-slip faulting.

Primary paragneiss mineralogy consists of microcline, plagioclase, quartz, muscovite, and biotite (in order of abundance), with accessory myrmekite, hornblende, epidote, titanite, zircon, and opaques. Both the norms calculated from whole rock chemical analysis and thin section modes plot in the granite and granodiorite fields of the IUGS QAP classification. Plagioclase augen (3-5 mm) are polycrystalline in thin section; rounded feldspar porphyroclasts (2-5 cm) are isolated in outcrop. Microprobe analysis of plagioclase indicates the augen range in composition from An21 to An34 with coexisting matrix plagioclases generally slightly more sodic. Major element whole rock chemistry indicates that these rocks are calc-alkaline in nature. REE are LREE enriched, with all REE being 10-50 times enriched relative to C1 chondrites.