METATEXIS

the process in which the magma-like portion of migmatites (mixed rocks that have granitic layers or veinlike bodies) is emplaced within a host rock of different composition. Migmatites may form by the injection of granitic magma (the metatect) into the host or by the partial fusion of the host itself; they form under the most extreme temperatures and pressures reached during regional metamorphism and are generally associated with rocks of the granulite facies. Such rocks, considered to represent the deeper parts of folded mountain belts, are often associated with large granitic bodies. The origin of these granites is closely tied to the migmatites because the metamorphic or igneous origin of the latter may be extrapolated to interpret the origin of the granitic body.