MIGMATITE

in geology, rock composed of a metamorphic (altered) host material that is streaked or veined with granite rock; the name means mixed rock. Such rocks are usually gneissic (banded) and acidic rather than basic in composition; they may occur on a regional scale in areas of high-grade metamorphism. Many migmatites probably represent the partial fusion of the metamorphic host during extreme metamorphism; the components of the rock with the lower melting temperatures are fused and gather to produce the streaks of granite. The migmatites of some Precambrian metamorphic terrains may be the result of this process. Migmatite also can form near large intrusions of granite when some of the magma is injected into the neighbouring metamorphic rocks.