coupled with an increasing melt fraction, alters the deformation mechanisms acting among grains and decreases the strength of the rock significantly. Melt filled pores eventually coalesce and melt flow parallel to the elongation lineation of grains (or along planes of foliation) is promoted. As a rock partially melts and begins to flow, its rheology changes significantly. Such changes will localize the strain created by regional tectonics and as per Le Chatelier's Principle, the system responds by pumping melt towards zones of dilatancy (lower pressure) thereby segregating the melt from its anatectic source on a local scale. Where this has occurred and been preserved in the rock record, one can expect to see macroscopic melt-rich layers (leucosomes), and macroscopic residual solid layers (melanosomes). These layers will commonly be oriented parallel to the fabric of the host rock. As the amount of accumulated melt in the surrounding rock increases, melt will travel further from its source towards growing transverse structures such as the aforementioned embrittlement fractures. Eventually, this leads to the formation and development of an interconnected accumulation network. Emplacement When the transport of melt occurs on larger scales, anatexis can lead to the ascent and emplacement of large granitic bodies in the upper crust. This transition is generally marked by the change from shear-driven melt migration to buoyancy-driven melt migration. This final step in the extraction process requires an optimal balance between melt fraction and melt distribution in the local rock. The ascent of this magma, while previously thought to have occurred as large, slow-rising and buoyant bodies, is now largely attributed to fast-moving narrow conduits and self-propagating dykes. These faster moving models have overcome major thermal and mechanical problems embedded in older theories as well as the granite problem and near surface felsic volcanism. As the flow of rising magma then changes from vertical back to horizontal, emplacement is initiated. This process is episodic and accommodated by both ongoing regional tectonics and emplacement-generated wall rock structures allowing the pluton to spread laterally and thicken vertically. Syntectonic anatectic migmatites at Hafafit region, Eastern Desert, Egypt, Nubian Shield provide an example of the close relation between orogeny (tectonic), metamorphism and granite generation and emplacement. See also Granite Migmatite References Further reading M. Dolores Pereira Gómez, etal.: Duality of Cordierite Granites related to Melt-Restite Segragation in the Peña Negra Anatectic Complex, Central Spain.The Canadian Mineralogist. Vol. 38, pp. 1329-1346 (2000) Igneous petrology Metamorphic