High Quality Content by WIKIPEDIA articles! Ultrahigh-Pressure (UHP) Metamorphism refers to metamorphic processes at pressures high enough to stabilize coesite, the high-pressure polymorph of SiO2. It is important because the processes that form and exhume UHP rocks may strongly affect plate tectonics, the composition of Earth`s crust, and the evolution of Earth`s crust. The discovery of UHP metamorphic rocks in 1984 revolutionized our understanding of plate tectonics. Prior to 1984 there was little suspicion that continental rocks could reach such high pressures.