AMPHIBOLITES AS A TOOL FOR FINGERPRINTING TERRANES IN THE BLUE RIDGE OF WESTERN NORTH CAROLINA

Mafic and ultramafic rocks in southwestern North Carolina have distinctive field and geochemical characteristics that may serve as useful tools for helping to fingerprint different litho-tectonic packages in the Blue Ridge of the Southern Appalachians. In southwestern NC, significant exposures of mafic rocks (amphibolites) are intimately associated with the Buck Creek, Carroll Knob, and Lake Chatuge ultramafic bodies. Major-element, trace-element, and REE geochemical analyses of these amphibolites are consistent with oceanic gabbro/cumulate protoliths. To the NE in the vicinity of the Webster-Addie and Balsam Gap/Dark Ridge ultramafic bodies, mafic amphibolites form isolated bodies, generally not in contact with the ultramafic rocks. Major-element, trace-element, and REE analyses of these amphibolites differ from amphibolites to the SW and are more consistent with intermediate, subduction-related igneous protoliths. In order to test the persistence of these differences and potential utility as a fingerprint for different terrane origins we have collected amphibolite samples from along and across strike, mostly to the north of the Webster-Addie area and analyzed for major and trace-element geochemistry. In addition we have begun to compile geochemical data for Blue Ridge amphibolite samples from the literature. An interesting result is that the geochemistry of amphibolite samples, collected from isolated bodies within the central Blue Ridge (Mars Hill terrane) to the west of the Holland Mountain fault or Burnsville shear zone, cluster with amphibolites from the Webster-Addie area. The amphibolite bodies sampled to the northeast of Webster-Addie in the Willets-Balsam area, and in the Canton, Sandymush, Enka, Weaverville, and Marshall Quadrangles range from outcrop- to map-scale. All appear to be hosted in a heterogeneous package of granitic to amphibolitic and locally migmatitic orthogneisses, which include ultramafic bodies as a minor constituent. Our observations suggest a connection between the host rocks of the Webster-Addie body and the enigmatic Mars Hill Terrane worthy of further exploration. Amphibolite geochemistry, in combination with detailed mapping and geochronology, may be a useful tool in fingerprinting complexly metamorphosed terranes of different origin.