including erosion, tectonic denudation, and lithospheric thinning. Volatile content The amount of water available in the system plays a major role in controlling the degree of melting at a given temperature. Low water availability will suppress melting. Furthermore, the degree of water saturation of a system will affect the composition of any melt generated. Water can be derived from a variety of sources, including from surrounding country rocks (pore water) or from the decomposition of hydrous minerals (e.g. micas, amphiboles). Melting reactions involving water liberated from hydrous minerals are often referred to as dehydration melting reactions or vapour-absent reactions. Over time, dehydration melting reactions will consume all of the hydrous phases in a rock, meaning that the amount of melt generated through these reactions is controlled by the abundance and stability of specific hydrous phases. Depending on the tectonic setting, water can also be introduced to the system through the dehydration of a subducting hydrated oceanic plate or magmatic underplating. Rock type The composition of a parent rock has a direct effect on the composition of the resulting melt. Granitic melts are commonly classified based on the nature of their source rock. One of the more popular classification schemes for granites was first introduced by White and Chappell in 1974. This classification scheme categorizes granites based on whether they are the result of the melting of sedimentary rocks (S-type granites) or the melting of igneous rocks (I-type granites). This genetic difference is reflected in the geochemical signature of the melts themselves. Syntectonic crustal anatexis Where partial melting is associated with regional tectonics and differential stresses, the production of melt creates instabilities in pore spaces and eventually along grain-boundaries that localize strain into crustal-scale shear zones. These zones promote melt flow out of the anatectic system as a mechanism to accommodate strain which in turn promotes more partial melting. The feedback loop that develops between the advancement of deformation and partial melting is referred to as syntectonic crustal anatexis. Syntectonic anatectic migmatites at Hafafit region, Eastern Desert, Egypt as a part of the Nubian Shield are a good example of such crustal melts. Melt segregation 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. Such reactions produce large positive volume changes within the metamorphic system causing melt enhanced embrittlement. This,