Ultramafictometapelitic

Ultramafictometapelitic is a nonstandard term used in some geological writings to describe rocks or rock sequences that exhibit characteristics spanning ultramafic and metapelitic compositions. It is not part of the formal, widely adopted mineralogical or lithological classification, but it can be employed to indicate a continuum or juxtaposition of ultramafic and pelitic metamorphic material within a single locality or tectonic unit.

In practice, ultramafictometapelitic assemblages may form in complex tectonic settings where ultramafic mantle-derived rocks (such as peridotites or serpentinites) interact with pelitic, clay-rich sedimentary sequences during metamorphism. Metamorphic processes such as dehydration, metasomatism, and high-temperature dehydration reactions can lead to mineralogical zonation, creating rocks that range from ultramafic to metapelitic in their dominant mineral assemblages. The ultramafic portion typically contains minerals like olivine, pyroxene, serpentine, and chlorite, while the metapelitic portion yields aluminous minerals such as garnet, muscovite, biotite, and sillimanite group minerals, often with quartz as an associated phase.

Overall, the concept highlights a gradient or composite nature rather than a single, uniform composition. It is sometimes discussed in studies of ophiolitic belts, subduction-zone metamorphism, or tectonically mixed terranes where ultramafic and pelitic materials have experienced shared yet heterogeneous metamorphic histories.