Editing Peridotite (section)

==Origin==
[[File:Peridotite mantle xenoliths in phonotephrite (Peridot Mesa Flow, Middle Pleistocene, 580 ka; Peridot Mesa, San Carlos Volcanic Field, Arizona, USA) 30.jpg|thumb|Peridotite [[xenolith]]s in [[phonotephrite]], from Arizona]]
Peridotites have two primary modes of origin: as mantle rocks formed during the accretion and differentiation of the Earth, or as cumulate rocks formed by precipitation of olivine ± pyroxenes from basaltic or ultramafic magmas. These magmas are ultimately derived from the [[upper mantle (Earth)|upper mantle]] by partial melting of mantle peridotites.{{sfn|Philpotts|Ague|2009|p=2, 370–374, 384–390}}

Mantle peridotites are sampled as ophiolites in collisional mountain ranges, as xenoliths in basalt or kimberlite, or as abyssal peridotites (sampled from ocean floor).<ref name="refname"/> These rocks represent either fertile mantle (lherzolite) or partially depleted mantle (harzburgite, dunite).{{sfn|Philpotts|Ague|2009|pp=43–44, 370–374, 385, 391, 590, 601–604}} Alpine peridotites may be either of the ophiolite association and representing the uppermost mantle below ocean basins, or masses of subcontinental mantle emplaced along thrust faults in mountain belts.<ref>{{cite journal |last1=Gueydan |first1=Frédéric |last2=Mazzotti |first2=Stephane |last3=Tiberi |first3=Christel |last4=Cavin |first4=Remy |last5=Villaseñor |first5=Antonio |title=Western Mediterranean Subcontinental Mantle Emplacement by Continental Margin Obduction |journal=Tectonics |date=June 2019 |volume=38 |issue=6 |pages=2142–2157 |doi=10.1029/2018TC005058|bibcode=2019Tecto..38.2142G |s2cid=182877329 |url=https://hal.umontpellier.fr/hal-02262198/file/Gueydan_et_al-2019-Tectonics.pdf }}</ref>

Layered peridotites are igneous sediments and form by mechanical accumulation of dense olivine crystals.<ref>{{Cite journal|last1=Emeleus|first1=C. H.|last2=Troll|first2=V. R.|date=2014-08-01|title=The Rum Igneous Centre, Scotland|journal=Mineralogical Magazine|language=en|volume=78|issue=4|pages=805–839|doi=10.1180/minmag.2014.078.4.04|bibcode=2014MinM...78..805E|issn=0026-461X|doi-access=free}}</ref> They form from mantle-derived magmas, such as those of basalt composition.{{sfn|Philpotts|Ague|2009|p=384}} Peridotites associated with Alaskan-type ultramafic complexes are cumulates that probably formed in the root zones of volcanoes.<ref>{{cite journal |last1=Himmelberg |first1=G.R. |last2=Loney |first2=R.A. |title=Characteristics and petrogenesis of Alaskan-type ultramafic-mafic intrusions, Southeastern Alaska |journal=U.S. Geological Survey Professional Paper |series=Professional Paper |date=1995 |volume=1564 |doi=10.3133/pp1564|hdl=2027/uc1.31210017370071 |doi-access=free |hdl-access=free }}</ref> Cumulate peridotites are also formed in [[komatiite]] lava flows.<ref>{{cite journal |last1=Szilas |first1=Kristoffer |last2=van Hinsberg |first2=Vincent |last3=McDonald |first3=Iain |last4=Næraa |first4=Tomas |last5=Rollinson |first5=Hugh |last6=Adetunji |first6=Jacob |last7=Bird |first7=Dennis |title=Highly refractory Archaean peridotite cumulates: Petrology and geochemistry of the Seqi Ultramafic Complex, SW Greenland |journal=Geoscience Frontiers |date=May 2018 |volume=9 |issue=3 |pages=689–714 |doi=10.1016/j.gsf.2017.05.003|s2cid=32485665 |doi-access=free |bibcode=2018GeoFr...9..689S }}</ref>