What is anatexis in geology ?

Anatexis : definition

Anatexis is a large-scale geological process in which rocks subjected by burial at increasingly high temperatures, undergo a partial fusion giving migmatites (also called anatexites). These rocks are made up of alternating light levels (magmatic granite) and dark levels (metamorphic). The clear levels are composed of quartz (gray) and feldspar (white) - Source C. Nicollet. By pushing the process further,
the rate of fusion is higher and the magmatic liquid can migrate. As it cools, this magma gives rise to magmatic rocks called "anatexis".

The onset of fusion depends on many factors, in particular the chemistry of the rocks, the total pressure and the water concentration (lowering of the melting point if the rocks are hydrated).