Anatexis (via Latin from Greek roots meaning "to melt down") is the partial melting of rocks. Traditionally, anatexis is used specifically to discuss the partial melting of crustal rocks, while the generic term "partial melting" refers to the partial melting of all rocks, in both the crust and mantle. Anatexis can occur in a variety of different settings, from zones of continental collision to mid-ocean ridges. It is believed that anatexis is the process largely responsible for the formation of migmatites. Furthermore, scientists have recently discovered that partial melting plays an increasingly important role in active crustal processes, including the advancement of active deformation and the emplacement of crustal granites. As a result, active feedback between crustal shearing, melting, and granite emplacement has become largely accepted in the place of large scale, unreasonable models involving fractional melting of the mantle into granitic batholiths and plutons. Evidence for this can be seen in the physical, mineralogical, and isotopic signatures of countless granites. Conditions for melting Crustal anatexis is not restricted to a single tectonic setting, but rather is controlled by four primary parameters: temperature, pressure, volatile content, and rock type/composition. These parameters are highly variable and depend on depth, crustal thickness, and local variations of the Earth's geotherm. The amount and composition of partial melts likely varies locally, reflecting the heterogeneity of the Earth's crust. Temperature In order to induce crustal melting, the temperature must be increased past the normal geotherm. Possible sources of heat include primordial heat originating from the core of the Earth as well as the decay of radioactive elements. This heat is distributed throughout the Earth's crust by a number of different processes, including radiation, conduction, convection, and advection. The emplacement of magmatic intrusions is also commonly associated with local increases in temperature. If the increase in temperature is sufficient, this can lead to partial melting of adjacent country rocks. If partial melting does occur, then the degree of melting is controlled by the amount of available heat in the magmatic body. Pressure Beneath the Earth's surface, pressure increases with depth due to the accumulation of overlying rock. At a given temperature, a decrease in pressure can result in localized melting. Melting that is caused by a drop in pressure is referred to as decompression melting. Decompression melting can occur in thickened portions of the Earth's crust and may be the result of a variety of processes,