USING MINERALOGY AND MINERAL CHEMISTRY TO CORRELATE MAFIC ROCK UNITS IN THE SOUTHERN BLUE RIDGE

A series of mafic-ultramafic complexes and smaller mafic bodies are enclosed within pelitic schists and gneisses of the North Carolina Blue Ridge Mountains, southwest of Franklin, NC. Several different origins have been proposed for these bodies (i.e., Hatcher et al 1984; Meen et al 1988; Peterson et al, in press), though there appear to be geochemical similarities among them (i.e., Berger et al 2001). We are currently examining amphibolite samples from three of these units (the Buck Creek/Chucky Gal complex, the Carroll Knob complex, and the Kimsey Bald mafic body) to assess the possible relationships among the units, and to further constrain their metamorphic histories.

Representative amphibolite samples were prepared from mafic units in each body, and were analyzed for their mineralogical compositions using both microscopic petrography and the remotely operable JEOL 8900R Superprobe electron microprobe housed at FCAEM at Florida International University. Preliminary results indicate the samples possess similar primary mineralogies, consisting of hornblende + plagioclase ± epidote ± ilmenite ± titanite, with minor quartz and small, rare, accessory zircons. Carroll Knob and Kimsey Bald amphibolites include garnet, which is not observed in typical Buck Creek amphibolites; zoisite was encountered in one Carroll Knob amphibolite; and scapolite is found in some Buck Creek amphibolites, along with relict clinopyroxene. Hornblende and plagioclase compositions are variable among the units.

Our preliminary estimates of metamorphic grade for these units are consistent with the very high-grade conditions inferred by Tenthorey et al (1996) and Lang et al (2004) for Buck Creek. Thus far, our results are consistent with the contention of Ryan et al (2006) that all western Blue Ridge mafic/ultramafic units may be part of a single fragmented ophiolitic sheet, although their retrograde metamorphic paths appear to differ.