High Quality Content by WIKIPEDIA articles! Ultrahigh-temperature metamorphism (UHT) represents extreme crustal metamorphism with metamorphic temperatures exceeding 900 °C.Granulite-facies rocks metamorphosed at very high temperatures were identified in the early 1980s, although it took another decade for the geoscience community to recognize UHT metamorphism as a common regional phenomenon. Petrological evidence based on characteristic mineral assemblages backed by experimental and thermodynamic relations demonstrated that Earth’s crust can attain and withstand very high temperatures (900-1000 °C) with or without partial melting.