The Wayah granulite-facies metamorphic core, southwestern North Carolina: High-grade culmination of Taconic metamorphism in the southern Blue Ridge

The Wayah granulite-facies metamorphic core, in the eastern Blue Ridge, southwestern North Carolina, contains the metamafic assemblage hornblende-orthopyroxene-clinopyroxene which defines the hornblende (lower) granulite facies. The metamorphic progression from the kyanite-almandine zone into the Wayah granulite core is continuous across the Hayesville fault, a major premetamorphic-peak tectonostratigraphic boundary. This metamorphic transition includes a distinct muscovite-absent (+alkali feldspar) second-sillimanite zone. Retrogression is limited. This entire range in metamorphic grade apparently was produced during a single, prograde, Paleozoic (likely Taconic) metamorphic event.

The Hayesville fault crosses the study area mostly within the first-sillimanite zone, northwest of the Wayah granulite core. Both supracrustal sequences juxtaposed along this fault consist predominantly of metasedimentary rocks probably deposited during the Late Proterozoic. Although paragneiss pre-dominates, the southeastern terrane is distinguished by the presence of metamorphosed felsic, mafic, and ultramafic igneous rocks. No evidence supports the presence of Grenville basement within the study area.

The second of four deformational events, synchronous with the metamorphic peak, created northeast-southwest- to east-west-trending, upright isoclinal folds which dominate the outcrop pattern. Macroscopic F₂ folds deformed the Hayesville fault.

Application of mineralogic thermometry and barometry yields conditions which range from 585 °C, 5.5 kb at the kyanite-sillimanite isograd to 842 °C, 9.8 kb in the hornblende granulite facies. Macroscopic distributions of migmatite and perthite, published experimental data, and barometric calculations suggest that T = ∼669 °C, P = ∼6.52 kb, and X(H₂O) = ∼0.62 at the second-sillimanite isograd.

Results indicate that the Wayah granulite-facies core constitutes the high-grade culmination of Paleozoic metamorphism in the southern Appalachian Blue Ridge.