Editing Gneiss (section)

==Occurrences==
[[File:Road Cutting - geograph.org.uk - 820828.jpg|thumb|Dark dikes (now [[Foliation (geology)|foliated]] [[amphibolite]]s) cutting light grey Lewisian gneiss of the Scourie complex, both deformed and cut by later (unfoliated) pink granite dikes]]
[[File:Yttre Ursholmen Kontakt Kosterdiabas i Nebulitisk-migmatitisk sedimentgnejs.jpg|thumb|Contact between a dark-colored [[diabase]] dike (about 1100 million years old)<ref name="hageskov">Bjørn Hageskov (1985): [http://2dgf.dk/xpdf/bull34-03-04-151-197.pdf ''Constrictional deformation of the Koster dyke swarm in a ductile sinistral shear zone, Koster islands, SW Sweden.''] Bulletin of the Geological Society of Denmark 34 (3–4): 151–97</ref> and light-colored [[Migmatite|migmatitic]] paragneiss in the [[Kosterhavet National Park]] in the [[Koster Islands]] off the western coast of Sweden.]]
[[File:Gnaisse Sete Voltas - Bahia - Brasil.jpg|thumb|Sample of Sete Voltas gneiss from [[Bahia]] in Brazil, the oldest rock outcropping in the crust of South America, {{circa}} 3.4 billion years old (Archean)]]
Gneisses are characteristic of areas of [[regional metamorphism]] that reaches the middle [[amphibolite]] to [[granulite]] [[metamorphic facies]]. In other words, the rock was metamorphosed at a temperature in excess of {{convert|600|C||sp=us}} at pressures between about 2 to 24 [[kbar]]. Many different varieties of rock can be metamorphosed to gneiss, so geologists are careful to add descriptions of the color and mineral composition to the name of any gneiss, such as ''garnet-biotite paragneiss'' or ''grayish-pink orthogneiss''.{{sfn|British Geological Survey|1999|pp=5-6}}

===Granite-greenstone belts===
[[Shield (geology)|Continental shields]] are regions of exposed ancient rock that make up the stable cores of continents. The rock exposed in the oldest regions of shields, which is of [[Archean]] age (over 2500 million years old), mostly belong to granite-greenstone belts. The [[greenstone belt]]s contain [[Metavolcanic rock|metavolcanic]] and [[metasedimentary rock]] that has undergone a relatively mild grade of metamorphism, at temperatures of {{cvt|350-500|C||}} and pressures of {{cvt|200-500|MPa|bar}}. The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over {{cvt|500|C||}}) metamorphism to the amphibolite or granulite facies. These form most of the exposed rock in Archean [[craton]]s.<ref>{{cite book |last1=Kearey |first1=P. |last2=Klepeis |first2=Keith A. |last3=Vine |first3=Frederick J. |title=Global tectonics. |date=2009 |publisher=Wiley-Blackwell |location=Oxford |isbn=9781405107778 |page=350 |edition=3rd}}</ref>

===Gneiss domes===
Gneiss domes are common in [[orogenic belts]] (regions of mountain formation).<ref>{{cite book|last1=Whitney |first1=D.L |last2=Teyssier |first2=C. |last3=Vanderhaeghe |first3=O.  |year=2004 |chapter=Gneiss domes and crustal flow |editor-last1=Whitney |editor-first1=D.L.  |editor-last2=Teyssier |editor-first2=C. |editor-last3=Siddoway |editor-first3=C.S. |editor3-link= Christine Siddoway|title=Gneiss domes in orogeny: Boulder, Colorado, Geological Society of America Special Paper 380 |url=https://www.researchgate.net/publication/309201751 |access-date=5 July 2021}}</ref> They consist of a dome of gneiss intruded by younger granite and migmatite and mantled with sedimentary rock.<ref>{{cite journal |last1=Teyssier |first1=Christian |last2=Whitney |first2=Donna L. |title=Gneiss domes and orogeny |journal=Geology |date=1 December 2002 |volume=30 |issue=12 |pages=1139–1142 |doi=10.1130/0091-7613(2002)030<1139:GDAO>2.0.CO;2|bibcode=2002Geo....30.1139T }}</ref> These have been interpreted as a [[geologic record]] of two distinct mountain-forming events, with the first producing the granite basement and the second deforming and melting this basement to produce the domes. However, some gneiss domes may actually be the cores of [[metamorphic core complex]]es, regions of the deep crust brought to the surface and exposed during extension of the [[Earth's crust]].<ref>{{cite book |last1=Yin |first1=A. |year=2004 |chapter=Gneiss domes and gneiss dome systems |editor-last1=Whitney |editor-first1=D.L. |editor-last2=Teyssier |editor-first2=C. |editor-last3=Siddoway |editor-first3=C.S.|editor3-link= Christine Siddoway|title=Gneiss domes in orogeny |publisher=Geological Society of America |id=Special Paper 380 |location=Boulder, Colorado|pages= 1–14 |url=https://faculty.epss.ucla.edu/~yin/05-Publications/papers/085-Yin-2004-GSA%20Special%20papers.pdf |access-date=4 July 2021}}</ref>

===Examples===
<!-- This is not a comprehensive list of gneisses. Include only examples that have something particularly notable about them or that show the global occurrence of gneiss. -->

* The [[Acasta Gneiss]] is found in the [[Northwest Territories]], [[Canada]], on an island about {{convert|300|km||sp=us}} north of [[Yellowknife]]. This is one of the most ancient intact crustal fragments on Earth, metamorphosed 3.58 to 4.031 billion years ago.<ref>[http://www2.ess.ucla.edu/~schauble/Isotope_geochemistry/Acasta_Concordia_Bowring.pdf Bowring, S.A., and Williams, I.S., 1999. Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada. Contributions to Mineralogy and Petrology, v. 134, 3–16]</ref>
*The [[Lewisian complex|Lewisian gneiss]] is found throughout the [[Outer Hebrides]] of Scotland, on the Scottish mainland west of the [[Moine Thrust Belt|Moine Thrust]], and on the islands of [[Coll]] and [[Tiree]].<ref>{{cite book |last1=Gillen |first1=Con |title=Geology and landscapes of Scotland |date=2003 |publisher=Terra |location=Harpenden |isbn=1-903544-09-2|page=44}}</ref> These rocks are largely igneous in origin, mixed with metamorphosed [[marble]], quartzite and mica schist with later intrusions of [[basaltic]] [[Dike (geology)|dikes]] and granite magma.<ref>{{cite book |last1=McKirdy |first1=Alan |title=Land of mountain and flood : the geology and landforms of Scotland |date=2007 |publisher=Birlinn |location=Edinburgh |isbn=978-1-84158-357-0|page=95}}</ref>
*The [[Morton Gneiss]] is an Archean-age gneiss exposed in the [[Minnesota River]] Valley of southwestern [[Minnesota]], United States.  It is thought to be the oldest intact block of continental crust in the United States.<ref name=Aber>{{cite web |last=Aber |first=James S. |title=Morton Gneiss, Minnesota |url=http://academic.emporia.edu/aberjame/tectonic/morton_gneiss/morton.htm |publisher=Emporia State University |year=2012 |accessdate=2019-05-22 |archive-date=2014-11-26 |archive-url=https://web.archive.org/web/20141126003847/http://academic.emporia.edu/aberjame/tectonic/morton_gneiss/morton.htm |url-status=dead }}</ref>
* The [[Peninsular Gneiss]] is a sequence of Archean gneisses found throughout the [[Indian Shield]] and ranging in age from 3400 to 2500 million years old.<ref name=monument>{{cite web|url=http://www.portal.gsi.gov.in/portal/page?_pageid=127,529567&_dad=portal&_schema=PORTAL|title=Peninsular Gneiss|publisher=Geological Survey of India|accessdate=2009-02-27|archive-url=https://web.archive.org/web/20110721161351/http://www.portal.gsi.gov.in/portal/page?_pageid=127,529567&_dad=portal&_schema=PORTAL|archive-date=21 July 2011|url-status=dead}}</ref><ref name= GSI>{{cite journal |title=National Geological Monuments, pages 96, Peninsular Gneiss, page29-32|journal=Special Publication Series|publisher=Geological Survey of India,27, Jawaharlal Nehru Road, Kolkata-700016|issn=0254-0436|year=2001|url=http://www.vedamsbooks.com/no24484.htm
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