igneousmetamorphic

Igneousmetamorphic is not a standard term in geology, but it is used informally to describe rocks that originated as igneous rocks and have subsequently undergone metamorphism, or metamorphic rocks that preserve igneous protoliths. In this sense, the concept emphasizes the origin of the material (igneous) combined with later metamorphic change that re-crystalizes minerals and alters texture and structure.

The central idea is the protolith, the original rock before metamorphism. Igneous protoliths commonly metamorphose into orthogneiss, granulite, eclogite, or metabasite, depending on their composition and the pressure–temperature conditions during metamorphism. High-temperature, low-water conditions can produce granulitic or granulite-facies rocks from granitic or other igneous precursors. Mafic igneous rocks may yield metabasites or eclogites under high-pressure conditions. Contact metamorphism near intrusions can create hornfels, which may retain some igneous textures while developing new mineral assemblages.

Migmatites are often cited in discussions of igneousmetamorphic rocks because they represent partial melting of metamorphosed rocks, producing igneous melt that intrudes the solid phase. Thus migmatites can bridge metamorphic and igneous processes, reflecting both melting and crystallization events in the crust.

Identification relies on textures and mineral assemblages that reveal both igneous origins and metamorphic overprinting. Metamorphic fabrics, recrystallization, and new mineral growth accompany changes in grain size and orientation, while preserved igneous features may indicate a granitoid or mafic protolith. Geochronology can help distinguish timing of igneous crystallization from later metamorphic events.