Частичное плавление горных пород и анатексис земной коры.

Partial melting of rocks
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. As a result, active feedback between crustal shearing, melting, and granite emplacement Evidence for this can be seen in the physical, mineralogical, and isotopic signatures of countless granites.

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. The amount and composition of partial melts likely varies locally, reflecting the heterogeneity of the Earth's crust. Possible sources of heat include primordial heat originating from the core of the Earth as well as the decay of radioactive elements. Decompression melting can occur in thickened portions of the Earth's crust and may be the result of a variety of processes, including erosion, tectonic denudation, and lithospheric thinning. This genetic difference is reflected in the geochemical signature of the melts themselves.

Segregation of granitic melts from their residual solids begins with the onset of partial melting along the grain boundaries of reactant minerals, namely the ferromagnesian phases of micas and amphiboles. This, coupled with an increasing melt fraction, alters the deformation mechanisms acting among grains and decreases the strength of the rock significantly. 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.

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.