Anatexis

As anatexis (Greek ανατηξις " melting" ), also migmatisation, defined as the partial melting of rocks of the Earth's crust as a result of increase in temperature, pressure relief and / or fluid intake ( eg, H2O, CO2). Anatexis found in the deep crust instead, usually over a period of mountain building processes, such as in the Himalayas and the Alps, but also in the Thuringian Forest. The resulting rocks are called migmatites and gneisses as migmatisierte, slate etc.

The initial stage of melting is called Metatexis. The mobilization takes place here only at the grain boundaries and affects only a portion of the mineral content ( partial melt ). In the higher stage, the Diatexis, increasingly, the dark ( mafic ) mineral constituents are melted until it finally comes to the formation of magma and igneous rocks. The more or less melted rocks ( Metatexite and Diatexite ) are summarized as migmatites (or Anatexite ).

In granitic rocks the anatexis takes place at temperatures above 650 ° C under fluid- saturated conditions. Typical pressures are 0.5 to 1 GPa ( corresponding to the pressure in 15 to 35 km depth ). Here, the quartz and feldspars are mainly melted. With rising temperatures, forming successive granitic, granodioritic and quarzdioritische melting. Alkaline rocks melt at much higher temperatures. Since quartzites, amphibolites and Kalksilikatfelse are almost never found in nature as Anatexite and are unchanged even in extended Migmatitgebieten as so-called Resisters, one estimates the maximum temperature is reached at a regional melting at about 800 ° C.