Granuliteforming

Granuliteforming refers to the metamorphic processes that generate granulite facies rocks, the high-temperature, relatively dry end of metamorphism that occurs in the middle to lower crust. Rocks formed under granulitefacies conditions are typically called granulites and display a granuloblastic texture, with grains that are closely packed and generally lack extensive foliation. The mineral assemblage commonly includes feldspar, quartz, orthopyroxene, clinopyroxene, and garnet, with accessory rutile, ilmenite, and magnetite; hydrous minerals such as biotite or hornblende are often absent or rare.

Formation conditions are characteristic of high temperatures, roughly 700 to 1000 degrees Celsius, and moderate to high pressures, on the order of 0.6 to 1.5 gigapascals. Granulite facies rocks are typically drier than rocks formed at lower-grade metamorphism, and dehydration melting can play a pivotal role. In many cases, dehydration of hydrous minerals during heating and tectonic thickening releases melts that segregate into leucosomes, leaving a dark melanosome-rich residue that records the granulite event.

Granuliteforming can proceed by solid-state reactions within a dry mineral system or accompany partial melting, producing granulite facies assemblages that retain evidence of high-temperature crustal processes. The resulting rocks contrast with lower-temperature facies such as amphibolite and with high-pressure eclogite, helping to constrain tectonothermal histories, crustal thickness changes, and exhumation pathways in continental crust.

Overall, granuliteforming is a key concept in metamorphic petrology for understanding deep-crustal metamorphism, crustal evolution, and the thermal history of ancient orogenic belts.