original_query: What is the definition of ultrahigh-temperature metamorphism (UHT) in geology?
query: What is the definition of ultrahigh-temperature metamorphism (UHT) in geology?
answer: Ultrahigh-temperature metamorphism (UHT) in geology is extreme crustal metamorphism with metamorphic temperatures exceeding 900 °C.  It's identified by robust thermobarometry or the presence of specific mineral assemblages.