Xenolith

Xenolith

:"This article concerns the geologic term, for other uses see: Xenolith (disambiguation)"A xenolith (Greek: 'foreign rock') is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term "xenolith" is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing lava on Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes.

Although the term xenolith is most commonly associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock. Xenoliths are sometimes found in recovered meteorites.

To be considered a true xenolith, the included rock must be identifiably different from the rock in which it is enveloped; an included rock of similar type is called an "autolith" or a cognate inclusion.

Xenoliths and xenocrysts provide important information about the composition of the otherwise innacessible mantle. Basalts, kimberlites, lamproites and lamprophyres, which have their source in the upper mantle, often contain fragments and crystals assumed to be a part of the originating mantle mineralogy. Xenoliths of dunite, peridotite and spinel lherzolite in basaltic lava flows are one example. Kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition. The aluminium-bearing minerals of these fragments provide clues to the depth of origin. Calcic plagioclase is stable to 25 km depth. Between 25 km and about 60 km, spinel is the stable aluminium phase. At depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral. Some kimberlites contain xenoliths of eclogite, which is considered to be the high-pressure metamorphic product of oceanic basaltic crust, as it descends into the mantle along subduction zones. (Blatt, 1996)

References

* Blatt, Harvey, and Robert J. Tracy (1996) "Petrology", W. H. Freeman, 2nd ed. ISBN 0-7167-2438-3


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Look at other dictionaries:

  • Xenolith — Xenolith, Mineral, derb, als Geschiebe in feinstängeligen u. faserigen Aggregaten; Härte = 7, specifisches Gewicht = 3,5; weiß, graulich, gelblich; Glasglanz, auf Spaltungsflächen Perlmutterglanz; durchscheinend; besteht aus Kieselerde u.… …   Pierer's Universal-Lexikon

  • xenolith — (n.) 1894, from XENO (Cf. xeno ) foreign, strange + lith (see LITH (Cf. lith )) …   Etymology dictionary

  • xenolith — [zen′əlith΄] n. [ XENO + LITH] Geol. a rock fragment different in kind from the igneous rock in which it is embedded xenolithic adj …   English World dictionary

  • Xenolith — Weißer Kalkstein Xenolith in rotbrauner Lava des Vesuvs, Italien Gerundeter Mantelxen …   Deutsch Wikipedia

  • xenolith — xenolithic, adj. /zen l ith/, n. Petrog. a rock fragment foreign to the igneous rock in which it is embedded. Also called inclusion. [1900 05; XENO + LITH] * * * ▪ geology       rock fragment within an intrusive igneous body that is unrelated to… …   Universalium

  • Xenolith (disambiguation) — Xenolith may refer to: *Xenolith is a geologic term for foreign rock fragment within a host rock. *Xenolith is the name of a Microsoft Windows Trojan identified in January, 1998. *Xenolith is a role playing game for the PC introduced in 2001 …   Wikipedia

  • xenolith — noun Date: 1894 a fragment of a rock included in another rock • xenolithic adjective …   New Collegiate Dictionary

  • xenolith — noun any piece of rock having a different origin to that of the igneous rock in which it is found …   Wiktionary

  • Xenolith — Xe|no|lith 〈m. 1 oder m. 23; Geol.〉 in magmatischem Gestein eingeschlossenes Fremdgestein [<Xeno... + ...lith] * * * Xe|no|lith [auch: ... lɪt], der; s u. en, e[n] [↑ lith] (Geol.): Fremdkörper, Einschluss in Ergussgesteinen …   Universal-Lexikon

  • Xenolith — Xe|no|lith 〈m.; Gen.: (e)s od. en, Pl.: e od. en; Geol.〉 in magmatischem Gestein eingeschlossenes Fremdgestein [Etym.: <Xeno… + …lith] …   Lexikalische Deutsches Wörterbuch

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