An example of migmatite origin by dehydrating metamorphism

An unusual type of garnetiferous migmatite has been studied at Tåbor (Moldanubicum of southern Bohemia) characterized by a coarse patchy quartzo-felspathic neosome with conspicuously large garnet crystals and a biotite paragneiss paleosome. The neosome is very different in textural and mineralogical appearance from the paleosome. Nevertheless, the chemical compositions of both migmatite components are very similar except for the contents of water, manganese, iron, and some trace elements. This indicates that the migmatite was formed in a process of metamorphic recrystallization from a previously homogeneous biotite paragneiss. Variation in water pressure during recrystallization (migmatization) under the conditions of low-pressure and high-temperature metamorphism is probably responsible for the mineralogical differences between the neosome and the paleosome