Formation of kyanite-bearing migmatites in the Central Adirondacks

Sillimanite-rich, S-type, granitic migmatites exposed at Ledge Mountain represent the only location in the Adirondack Highlands where kyanite has been found. The texturally young kyanite overprints sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought. The rare mineral assemblage of kyanite-garnet-potassium feldspar, decreasing Ti concentrations, and resorption between zircon domains indicate anatexis occurred during retrograde metamorphism from peak temperatures to peak pressures. U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites show anatexis continuing after high-grade metamorphism is believed to have ceased in the range. A new conceptual model reflecting a gneiss core complex, rather than an allochthonous block, is consistent with these findings.