Mantle Xenoliths

Dear Colleagues,

Xenoliths in mafic volcanic rocks can be metaphorically regarded as “messengers of the interior of the Earth”; likewise, meteorites have been referred to as “messengers of celestial bodies”. In both cases, their “messages” are never so plain and clear, hence deserving a lot of study to be correctly deciphered. Meteorites and xenoliths both share some characteristics. Both, for example, have a small size. Both experience transient physicochemical conditions which are quite different from those in their original environments. Both are relatively rare, and hence, only one sample, a few centimeters in size, may provide useful information on its original geological (or astronomical, in case of meteorites) setting.

A xenolith suite from a given volcanic structure, such as a tuff-breccia pipe (diatreme), can provide a snapshot of the composition of the buried section of the regional lithosphere, far of reach of the deepest drillings. Fragments from upper mantle and lower crust form, of course, the most appealing types among xenoliths. In fact, mantle and lower crust rarely crop out to allow direct field and laboratory investigation. Moreover, in those cases where tectonic uncovering of upper mantle has occurred, such as in some orogenic contexts and in oceanic fracture zones, the outcropping mantle-rocks experienced severe hydrous and oxidative alteration and mechanic deformation. By contrast, mantle xenoliths generally display original minerals and texture.

Mantle xenoliths often bear mineral assemblages in thermodynamic equilibrium   which allow pressure and temperature estimates according to established mineralogical geothermobarometers. If a given xenolith suite adequately represents the lithospheric column, a xenolith-based paleogeotherm can be calculated.

Mantle xenoliths sometimes host exotic minerals, such as hydrous-silicate or carbonate phases, which can be either ascribed to interaction with the host magma or to metasomatic events deep within the mantle. The high-pressure allotrope of the carbon, diamond, can be one of these exotic minerals, especially in xenoliths from kimberlite pipes.

This Special Issue on mantle (and lower-crustal) xenoliths accepts research papers with both regional and general relevance, review papers, datasets, and viewpoint articles, which deal to the aforementioned topic. No limits are posed on the possible contributions, since great choirs needs different voices.

Dr. Vittorio Scribano
Dr. Sergei K. Simakov
Guest Editors

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