PETROLOGIC INVESTIGATION OF METAMORPHIC ROCKS AT GLADE GAP, CHUNKY GAL MOUNTAIN IN THE WESTERN NORTH CAROLINA BLUE RIDGE MOUNTAINS

Chunky Gal Mountain, located in the southwestern N.C. Blue Ridge Mountains, is a tectonic mélange largely consisting of greenschist, amphibolite, and granulite facies metamorphic rocks emplaced along the Chunky Gal Mountain Fault (Lacazette and Rust, 1089; Peterson, 2014). This research identifies and describes variations in the geochemical and mineralogical compositions of rocks exposed at Glade Gap on the eastern flank of Chunky Gal Mountain using data obtained by x-ray fluorescence, x-ray diffraction, and petrographic analysis. Prior studies (McElhaney and McSween, 1983) show that likely Chunky Gal Mountain protoliths include pelitic sedimentary and mafic to ultramafic igneous rocks. The objectives of this research are to construct a detailed description of rocks exposed at Glade Gap and to correlate their geochemical and mineralogical variations to specific protolith compositions. Major element oxide concentrations (wt %) of most Glade Gap samples are consistent with previous Chunky Gal studies reporting a pelitic protolith (SiO₂ = 66.1-77.0, CaO = 2.2-3.2, Fe₂O₃ = 2.5-7.7, MgO = 0.2-1.9, K₂O = 1.5 – 4.1 wt%) and a mafic protolith (SiO₂ = 44.2-53.6, CaO = 10.9-16.7, Fe₂O₃ = 7.0-14.3, MgO = 4.4-8.5, K₂O = 0.14-0.31 wt%) when plotted on an ACF diagram. Calc-silicate samples also are present (SiO₂ = 56.5, CaO = 19.7, Fe₂O₃ = 5.6, MgO = 1.4, K₂O = 2.8 wt%). Petrographic and XRD analysis show that mafic protolith samples are dominated by quartz + hornblende + plagioclase + chlorite + epidote. Pelitic protolith samples are dominantly characterized by quartz + biotite + phlogopite + garnet. Calc-silicate samples contain quartz + hornblende + biotite + phlogopite + calcite + epidote + titanite. Field relations suggest that rocks characteristic of mafic protoliths were emplaced east of the Chunky Gal Mountain Fault, while those characteristic of pelitic protoliths were emplaced west of the fault.