Commonly, migmatites occur below deformed metamorphic rocks that represent the base of eroded mountain chains, commonly within Precambrian cratonic blocks, Migmatites form under extreme temperature and pressure conditions during prograde metamorphism, when partial melting occurs in metamorphic paleosome.

The serpentinite is formed by the hydrous alteration and low-temperature metamorphic alteration of igneous ultramafic rocks. These rocks are composed of olivine and pyroxene in different ratios to form peridotite and pyroxenite.

Restite is the residual material left at the site of melting during the in place production of granite through intense metamorphism. Generally, restite is composed of a predominance of mafic minerals because these are harder to melt (see Bowen’s reaction series).

Migmatites form under extreme temperature and pressure conditions during prograde metamorphism, when partial melting occurs in metamorphic paleosome. Components exsolved by partial melting are called neosome (meaning ‘new body’), which may or may not be heterogeneous at the microscopic to macroscopic scale.

Most migmatites form when a solid metamorphic rock gets heated due to intrusion of magma (often granitic magma). The granite magma slowly cools and the heat flows into the surround country rock; now, the heat flows in and the metamorphic rock, initially ALL SOLID, heats up and begins to melt!

Serpentinite is a rock composed of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. The mineral alteration is particularly important at the sea floor at tectonic plate boundaries.

Diatexis is high-grade anatexis in which fusion may be complete. A migmatite is a megascopically composite rock comprising alternating layers or lenses of granitoid and schist or gneiss. Metatexis will produce a migmatite, diatexis will not.

The following definition is proposed: Metatexis is the process of segregation (usually of quartz and feldspar) by metamorphic differentiation and partial fusion. It follows that: A metatexite is a rock produced by metatexis and in which the migmatitic banding is evident (Plate 12).

Metatexis is the process of segregation (usually of quartz and feldspar) by metamorphic differentiation and partial fusion. Diatexis is high-grade anatexis in which fusion may be complete.

THE ROLE OF ANATEXIS The role of anatexis in the formation of migmatites has remained con- troversial since the well-known debate between Sederholm (1907, 1923, 1926, 1967) and Holmquist (1916, 1921). The term anatexis was proposed by Sederholm (1907, 1967, 49) for the process of refusion of material.