Geology and Petrogenesis of Mafic and Ultramafic Rocks of the Willets-Addie Area, Central Blue Ridge, NC

Rocks encountered in the Addie-Willets area of western North Carolina include migmatitic amphibolite gneisses, and highly deformed and variably altered dunites and pyroxenites of the WebsterAddie ultramafic complex. Detailed mapping results indicate that both mafic and ultramafic rocks occur as discrete cm- to km-scale bodies, locally in contact with each other, but more commonly enclosed in regionally extensive meta-sedimentary schists and gneisses. Evidence for high-temperature metamorphic conditions at moderate pressures (~ upper amphibolite facies) includes extensive migmatite development in the amphibolites and associated metasediments, extensive zones of talc+anthophyllite+vermiculite+chlorit e±amphibole and/or antigorite alteration adjacent to trondjhemite dikes within the dunites, and pervasive ductile deformation. Compositionally the amphibolites have predominantly andesitic protoliths with no clear petrogenetic relationships to the dunites. Ultramafic protoliths are geochemically and lithologically similar to smaller ultramafic bodies exposed in the Ellijay Creek and Balsam Gap areas, but distinct from ultramafic rocks found in “oceanic” mafic-ultramafic associations within the Buck Creek or Lake Chatuge complexes. The random, “block-in-matrix” association of the units in the Addie-Willets area at a variety of scales and the arc-like character of the mafic rocks are similar to what is observed in subduction-related mélange deposits. Our results are consistent with convergent margin origins, and emplacement of these units into an accretionary sequence that was subsequently buried, heated, and strongly deformed