xenolithrich

Xenolithrich is an informal petrological term used to describe igneous rocks that contain a high proportion of xenoliths, or foreign-rock fragments, embedded within a host matrix. A xenolith is a fragment of preexisting rock that becomes enclosed in magma or lava during emplacement or eruption, thus xenolithrich rocks exhibit many such inclusions and often show a marked contrast between the xenoliths and the surrounding material.

Formation and texture: Xenolith-rich textures arise when magma ascends, intrudes, or erupts through surrounding rock and mechanically or chemically drags along blocks and fragments. The xenoliths may derive from crustal or mantle lithologies and can range from coarse fragments to angular blocks. The host rock records subsequent cooling, metamorphism, and possible reaction between xenoliths and the groundmass, sometimes producing reaction halos or mineralogical disequilibrium.

Significance: The abundance and variety of xenoliths in such rocks provide direct samples of crustal and mantle material that would otherwise be unavailable. Analyses of xenoliths yield constraints on the composition, temperature, and pressure history of the source region, crustal contamination during magma evolution, and the processes of mantle extraction and magma mingling.

Xenolith vs xenocryst: Xenoliths are rock fragments; xenocrysts are foreign crystals. Both indicate a transport history within magmatic systems.

See also xenolith, mantle xenolith, stoping, xenocryst.