Editing Convergent boundary (section)

== Volcanism and volcanic arcs ==
{{See also|Volcanic arc}}

The oceanic crust contains hydrated minerals such as the [[amphibole]] and [[mica]] groups. During subduction, oceanic lithosphere is heated and metamorphosed, causing breakdown of these hydrous minerals, which releases water into the asthenosphere. The release of water into the asthenosphere leads to partial melting. Partial melting allows the rise of more buoyant, hot material and can lead to volcanism at the surface and emplacement of plutons in the subsurface.<ref>{{cite book|last1=Philpotts|first1=Anthony R.|last2=Ague|first2=Jay J.|title=Principles of igneous and metamorphic petrology|date=2009|publisher=Cambridge University Press|location=Cambridge, UK|isbn=9780521880060|pages=604–612|edition=2nd}}</ref> These processes which generate magma are not entirely understood.<ref>{{cite journal|last1=Castro|first1=Antonio|title=The off-crust origin of granite batholiths|journal=Geoscience Frontiers|date=January 2014|volume=5|issue=1|pages=63–75|doi=10.1016/j.gsf.2013.06.006|doi-access=free}}</ref>

Where these magmas reach the surface they create volcanic arcs. Volcanic arcs can form as island arc chains or as arcs on continental crust. Three [[igneous differentiation|magma series]] of volcanic rocks are found in association with arcs. The [[redox|chemically reduced]] [[tholeiitic magma series]] is most characteristic of oceanic volcanic arcs, though this is also found in continental volcanic arcs above rapid subduction (>7&nbsp;cm/year). This series is relatively low in [[potassium]]. The more oxidized [[calc-alkaline magma series|calc-alkaline series]], which is moderately enriched in potassium and incompatible elements, is characteristic of continental volcanic arcs. The [[alkaline magma series]] (highly enriched in potassium) is sometimes present in the deeper continental interior. The [[shoshonite]] series, which is extremely high in potassium, is rare but sometimes is found in volcanic arcs.<ref name=":0" /> The [[andesite]] member of each series is typically most abundant,{{sfn|Philpotts|Ague|2009|p=375}} and the transition from basaltic volcanism of the deep Pacific basin to andesitic volcanism in the surrounding volcanic arcs has been called the andesite line.<ref>{{cite encyclopedia|chapter-url=http://www.dnzb.govt.nz/dnzb/default.asp?Find_Quick.asp?PersonEssay=3M44|access-date=26 November 2020|last1=Watters|first1=W. A.|title=Marshall, Patrick|chapter=Marshall, Patrick 1869 – 1950|encyclopedia=Dictionary of New Zealand Biography|date=7 April 2006|archive-date=24 May 2010|archive-url=https://web.archive.org/web/20100524084033/http://dnzb.govt.nz/dnzb/default.asp?Find_Quick.asp%3FPersonEssay=3M44|url-status=live}}</ref><ref>{{cite journal|last1=White|first1=A. J. R.|title=Andesite line|journal=Petrology|series=Encyclopedia of Earth Science|date=1989|pages=22–24|doi=10.1007/0-387-30845-8_12|isbn=0-442-20623-2|doi-access=free}}</ref>