Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post- orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

This study combines field observations, mineral and whole-rock geochemistry, phase equilibrium modeling, U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon geochronology to investigate sillimanite-bearing felsic migmatites exposed on Ledge Mountain in the central Adirondack Highlands (New York, USA), part of an extensive belt mid-crustal rocks comprising hinterland Mesoproterozoic Grenville orogen. Phase modeling suggests minimum peak metamorphic conditions 960–1025 °C 11–12.5 kbar during Ottawan orogeny—significantly higher pressure-temperature than previously determined—followed by a period near-isothermal decompression, then isobaric cooling. Petrography reveals abundant melt-related microstructures, pseudosection models show presence at least ~15%–30% melt buoyancy-driven exhumation decompression. New data document late (re)crystallization ca. 1047 ± 5 1035 2 Ma following ultrahigh-temperature (UHT) metamorphism anatexis retrograde cooling path. Inherited cores give mean date 1136 Ma, which derivation these granulites partial melting older igneous rocks. The ferroan, anhydrous character is similar that 1050 Lyon Granite consistent with origin late- post-Ottawan extensional environment. We present model for development migmatitic gneiss dome Adirondacks exhumed deep crustal including Snowy Oregon anorthosite massifs UHT migmatites. Recognition meta-plutonic recording migmatite has significant implications behavior this formerly thickened