What is "migmatite"

n. (context geology English) Any rock of mixed appearance, being an intimate mixture of granite and older rock, specifically from intense metamorphism which partially melts the rock, causing it to recrystallize in a state intermediate between igneous and metamorphic.

Migmatite is a rock that is a mixture of metamorphic rock and igneous rock. It is created when a metamorphic rock such as gneiss partially melts, and then that melt recrystallizes into an igneous rock, creating a mixture of the unmelted metamorphic part with the recrystallized igneous part. They can also be known as diatexite.

Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally molten material, and are not generally the result of solid-state reactions. Commonly, migmatites occur within extremely deformed rocks that represent the base of eroded mountain chains, typically within Precambrian cratonic blocks.

Migmatites often appear as tightly, incoherently folded ( ptygmatic folds) dikelets, veins and segregations of light-colored granitic composition called leucosome, within dark-colored amphibole and biotite rich material called the melanosome. If present, the mesosome, intermediate in color between a leucosome and melanosome, is mostly a more or less unmodified remnant of the original parent rock ( protolith). The light-colored material has the appearance of having been mobilized or molten.