Ultrahigh-temperature (UHT) metamorphism occurs at extreme temperatures exceeding 900°C, often associated with tectonic plate collisions or deep burial of crustal rocks. UHT metamorphic rocks are significant in petrology for understanding the conditions of deep crustal metamorphism, the evolution of orogenic belts, and the processes of crustal melting.
Reference: Harley, S. L. (1998). “Ultrahigh-Temperature Metamorphism: A New Window on the Thermal Evolution of the Continental Crust.” Geology, 26(4), 315-318.