According to Grubenmann's classification of metamorphic rocks (1904), the lowermost depth zone of metamorphism, which is characterized by high temperatures (500 to 700 degrees C), mostly strong hydrostatic pressure, and low or no shearing stress. It produces rocks such as high-grade schists and gneisses, granulites, eclogites, and amphibolites. The concept includes effects of high-temperature contact metamorphism and metasomatism. Modern usage stresses temperature-pressure conditions (highest 1696 metamorphic grade) rather than the likely depth of zone. Also spelled catazone. Compare: mesozone; epizone.