Xenolithbearing

Xenolithbearing is a term used in petrology to describe rocks that contain xenoliths, which are fragments of preexisting rock embedded in a different host rock. The xenoliths are typically derived from the surrounding country rock and are carried to the surface or into deeper levels by magmatic or tectonic processes. The host rock is usually igneous, but xenoliths can also occur in metamorphic rocks.

Xenoliths form when magma or lava entrains chunks of wall rock during ascent, intrusion, or emplacement, or when tectonic blocks are incorporated into moving magmatic bodies. They may be mantle xenoliths (for example, peridotite or dunite), crustal xenoliths (such as granulite or amphibolite), or xenoliths of mixed lithologies. Their presence is especially common in basaltic and alkaline volcanic suites and in kimberlites, but they also occur in granitic and metamorphic rocks.

The study of xenolithbearing rocks yields direct information about rocks and conditions at depths not normally accessible. Mantle xenoliths can reveal the composition of the upper mantle, pressure–temperature histories, and metasomatic processes, while crustal xenoliths provide clues to the composition and evolution of the crust at the time of entrainment. Attributes of xenoliths—mineralogy, texture, alteration, and zoning—aid in reconstructing magmatic histories and tectonic settings. In petrographic descriptions, researchers note xenolith abundance, size distribution, lithology, and whether xenoliths or xenocrysts preserve evidence of reaction with the host rock.

Kimberlites and other mantle-derived volcanic rocks are well known for abundant mantle xenoliths and, in some regions, associated diamonds.