Editing Xenolith

{{Short description|Rock inside a rock with a different composition}}
[[File:Xenolith in andesite (Tertiary; Yellowstone, Wyoming, USA) 6 (48555518367).jpg|thumb|[[Gabbro]]ic xenolith in andesite, [[Tertiary]] of Wyoming, United States]]
[[File:Iddingsite.JPG|thumb|[[Olivine]] [[weathering]] to [[iddingsite]] within a [[Mantle (geology)|mantle]] xenolith]]

A '''xenolith''' ("foreign rock") is a [[rock (geology)|rock]] fragment ([[Country rock (geology)|country rock]]) that becomes enveloped in a larger rock during the latter's development and solidification. In [[geology]], the term ''xenolith'' is almost exclusively used to describe [[inclusion (mineral)|inclusions]] in [[igneous rock]] entrained during [[magma]] ascent, emplacement and eruption.<ref>{{Cite journal|last1=Hansteen|first1=Thor H|last2=Troll|first2=Valentin R|date=2003-02-14|title=Oxygen isotope composition of xenoliths from the oceanic crust and volcanic edifice beneath Gran Canaria (Canary Islands): consequences for crustal contamination of ascending magmas|url=http://www.sciencedirect.com/science/article/pii/S000925410200325X|journal=Chemical Geology|language=en|volume=193|issue=3|pages=181–193|doi=10.1016/S0009-2541(02)00325-X|bibcode=2003ChGeo.193..181H|issn=0009-2541|url-access=subscription}}</ref> 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 body of lava on the 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 [[diamond]]s within [[kimberlite]] diatremes. Xenoliths can be non-uniform within individual locations, even in areas which are spatially limited, e.g. [[rhyolite]]-dominated lava of [[Nii-jima|Niijima]] volcano ([[Japan]]) contains two types of [[gabbro]]ic xenoliths which are of different origin - they were formed in different temperature and pressure conditions.<ref>{{Cite journal|last1=Arakawa|first1=Yoji|last2=Endo|first2=Daisuke|last3=Ikehata|first3=Kei|last4=Oshika|first4=Junya|last5=Shinmura|first5=Taro|last6=Mori|first6=Yasushi|date=2017-03-01|title=Two types of gabbroic xenoliths from rhyolite dominated Niijima volcano, northern part of Izu-Bonin arc: petrological and geochemical constraints|journal=Open Geosciences|volume=9|issue=1|pages=1–12|doi=10.1515/geo-2017-0001|bibcode=2017OGeo....9....1A|issn=2391-5447|doi-access=free}}</ref>

Although the term xenolith is most commonly associated with  inclusions in igneous rocks,<ref>{{Cite journal|last1=Troll|first1=Valentin R.|last2=Deegan|first2=Frances M.|last3=Jolis|first3=Ester M.|last4=Harris|first4=Chris|last5=Chadwick|first5=Jane P.|last6=Gertisser|first6=Ralf|last7=Schwarzkopf|first7=Lothar M.|last8=Borisova|first8=Anastassia Y.|last9=Bindeman|first9=Ilya N.|last10=Sumarti|first10=Sri|last11=Preece|first11=Katie|date=2013-07-01|title=Magmatic differentiation processes at Merapi Volcano: inclusion petrology and oxygen isotopes|url=http://www.sciencedirect.com/science/article/pii/S0377027312003253|journal=Journal of Volcanology and Geothermal Research|series=Merapi eruption|language=en|volume=261|pages=38–49|doi=10.1016/j.jvolgeores.2012.11.001|bibcode=2013JVGR..261...38T|issn=0377-0273|url-access=subscription}}</ref> a broad definition could also include rock fragments which have become encased in [[sedimentary rock]].<ref name="NatGeogXeno">{{cite web | url=https://www.nationalgeographic.org/encyclopedia/xenolith/ | title=Xenolith | publisher=[[National Geographic Society]] | work=Encyclopedic Entries | date=2011 | access-date=10 March 2018}}</ref><ref name="KomovEtAl">{{cite book | title=Geochemical Methods of Prospecting for Non-Metallic Minerals | publisher=CRC Press | last1=Komov | first1=I.L. | last2=Lukashev | first2=A.N. | last3=Koplus | first3=A.V. | year=1994 | location=Boca Raton | page=32 | isbn=978-1-4665-6457-2}}</ref> Xenoliths have been found in some [[meteorites]].<ref name="XenoLPI">{{cite web | url=https://www.lpi.usra.edu/science/Xenoliths/ | title=Xenoliths in Meteorites | publisher=[[Lunar and Planetary Institute]] | work=Science at LPI | access-date=10 March 2018}}</ref>

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 inaccessible [[Mantle (geology)|mantle]]. [[Basalt]]s, [[kimberlite]]s, [[lamproite]]s and [[lamprophyre]]s, which have their source in the [[upper mantle (Earth)|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 [[basalt]]ic lava flows are one example. Kimberlites contain, in addition to diamond xenocrysts, fragments of [[lherzolite]]s of varying composition. The [[aluminium]]-bearing minerals of these fragments provide clues to the depth of origin. Calcic [[plagioclase]] is stable to a depth of {{convert|25|km|abbr=on}}. Between {{convert|25|km|abbr=on}} and about {{convert|60|km|abbr=on}}, [[spinel]] is the stable aluminium phase. At depths greater than about 60&nbsp;km, dense [[garnet]] becomes the aluminium-bearing mineral. Some kimberlites contain xenoliths of [[eclogite]], which is considered to be the high-pressure [[Metamorphism|metamorphic]] product of basaltic [[oceanic crust]], as it descends into the mantle along [[subduction zone]]s.<ref>{{Cite book|title=Petrology: Igneous, Sedimentary, and Metamorphic|last1=Blatt|first1=Harvey|last2=Tracy|first2=Robert|publisher=W. H. Freeman|year=1996|isbn=0-7167-2438-3|edition=2nd}}</ref>

The large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a ''[[roof pendant]]''.

==Examples==
<gallery>
Image:Xenoliths_Little_Cottonwood_Canyon.JPG|Xenoliths in [[granodiorite]] of the Alta [[Stock (geology)|Stock]], [[Little Cottonwood Canyon]], Utah
Image:Sandstone xenolith Fairlee Pluton.jpg|Large xenolith of [[sandstone]] (probably from the Albee Formation) within the Fairlee [[Pluton]] in [[Vermont]]
Image:Peridotitic mantle xenolith.JPG|Peridotite (green) mantle xenolith within a (dark) [[volcanic bomb]] from [[Vulkaneifel]], Germany (coin of one euro for scale)
Image:Nephelinit.JPG|Rounded, yellow, weathered [[peridotite]] xenolith in a [[nephelinite]] lava flow at [[Kaiserstuhl (Baden-Württemberg)|Kaiserstuhl]], SW Germany
Image:Gneiss Inclusion in Granite Plate XLI Keyes 1895.jpg|Large xenolith of Baltimore [[Gneiss]] in the [[Guilford Quartz Monzonite]] in a wall of the old Waltersville Quarry, [[Granite, Maryland|Granite]], Maryland (about 1895)
Image:Lamprophyre with xenolith (Dubreuilville Dike, Archean; Route 17 roadcut southeast of Princess Lake & north of Wawa, Ontario, Canada) 26.jpg|[[Lamprophyre]] with xenolith at Ontario, Canada.
Image:Onion Xenolith.jpg|alt=Xenolith in granite|Xenolith in granite near [[Donner Pass]], California (foot for scale).
</gallery>

==References==
<references />

==Sources==
* Nixon, Peter H. (1987). ''Mantle Xenoliths''. J. Wiley & Sons. {{ISBN|0-471-91209-3}}.

== External links ==
{{commons category|Xenoliths}}

{{Authority control}}

[[Category:Igneous petrology]]