Metapelites

Metapelites are metamorphic rocks derived from pelitic sediments—predominantly clay-rich rocks such as shale, mudstone, or siltstone—that have undergone metamorphism. They are the metamorphic equivalents of pelites and are commonly formed during regional metamorphism in tectonically active areas.

During metamorphism, metapelites develop characteristic mineral assemblages that record temperature and pressure. At lower grades they typically contain chlorite, muscovite (or sericite), biotite, quartz, and plagioclase, sometimes with graphite or other minor minerals. As temperature and pressure rise, garnet appears and may be accompanied by staurolite or kyanite. In aluminous pelites, higher-grade conditions can yield sillimanite and cordierite, and in the hottest crustal conditions, garnet–cordierite–sillimanite or related assemblages may dominate. Accessory minerals such as zircon, tourmaline, and rutile help document the pressure–temperature history.

Metapelites are commonly foliated, with textures ranging from slaty to schistose to gneissic as metamorphism intensifies. They are often used as tracers of crustal processes, because their pelitic compositions preserve records of pressure–temperature evolution better than many other metamorphic rock types.

Geological settings include continental collision zones and subduction-related orogenesis, where pelitic sediments are buried and recrystallized over broad regions. The study of metapelites contributes to interpretations of tectonic evolution, metamorphic facies, and crustal differentiation.