Editing Asthenosphere (section)

== Magma generation ==
[[Decompression melting]] of asthenospheric rock creeping towards the surface is the most important source of [[magma]] on Earth. Most of this erupts at [[mid-ocean ridge]]s to form the distinctive mid-ocean ridge [[basalt]] (MORB) of the ocean crust.<ref>{{Cite journal |last1=Connolly |first1=James A.D. |last2=Schmidt |first2=Max W. |last3=Solferino |first3=Giulio |last4=Bagdassarov |first4=Nikolai |date=November 2009 |title=Permeability of asthenospheric mantle and melt extraction rates at mid-ocean ridges |journal=[[Nature (journal)|Nature]] |volume=462 |issue=7270 |pages=209–212 |bibcode=2009Natur.462..209C |doi=10.1038/nature08517 |pmid=19907492 |s2cid=4352616}}</ref><ref>{{cite journal |last1=Olive |first1=Jean-Arthur |last2=Dublanchet |first2=Pierre |date=November 2020 |title=Controls on the magmatic fraction of extension at mid-ocean ridges |journal=[[Earth and Planetary Science Letters]] |volume=549 |pages=116541 |bibcode=2020E&PSL.54916541O |doi=10.1016/j.epsl.2020.116541 |s2cid=224923541|doi-access=free }}</ref><ref>{{cite journal |last=Hofmann |first=A. W. |year=1997 |title=Mantle geochemistry: The message from oceanic volcanism |journal=[[Nature (journal)|Nature]] |volume=385 |issue=6613 |pages=219–228 |bibcode=1997Natur.385..219H |doi=10.1038/385219a0 |s2cid=11405514  |url=https://www.researchgate.net/publication/246759701 }}</ref> Magmas are also generated by decompressional melting of the asthenosphere above [[subduction zones]]<ref>{{cite journal |last1=Conder |first1=James A. |last2=Wiens |first2=Douglas A. |last3=Morris |first3=Julie |date=August 2002 |title=On the decompression melting structure at volcanic arcs and back-arc spreading centers: Arc and back-arc melting |journal=[[Geophysical Research Letters]] |volume=29 |issue=15 |pages=17–1–17-4 |doi=10.1029/2002GL015390 |s2cid=29842432|doi-access=free }}</ref> and in areas of [[continental rifting]].<ref>{{Cite journal |last1=Keen |first1=C.E. |last2=Courtney |first2=R.C. |last3=Dehler |first3=S.A. |last4=Williamson |first4=M.-C. |date=February 1994 |title=Decompression melting at rifted margins: comparison of model predictions with the distribution of igneous rocks on the eastern Canadian margin |journal=[[Earth and Planetary Science Letters]] |volume=121 |issue=3–4 |pages=403–416 |bibcode=1994E&PSL.121..403K |doi=10.1016/0012-821X(94)90080-9 }}</ref><ref>{{Cite journal |last=Sternai |first=Pietro |date=December 2020 |title=Surface processes forcing on extensional rock melting |journal=[[Scientific Reports]] |volume=10 |issue=1 |pages=7711 |bibcode=2020NatSR..10.7711S |doi=10.1038/s41598-020-63920-w |pmc=7206043 |pmid=32382159}}</ref>

Decompression melting in upwelling asthenosphere likely begins at a depth as great as {{convert|100 to 150| km|sigfig=1|sp=us}}, where the small amounts of volatiles in the mantle rock (about 100&nbsp;[[Parts per million|ppm]] of water and 60 ppm of [[carbon dioxide]]) assist in melting not more than about 0.1% of the rock. At a depth of about {{convert|70|km|sigfig=1|sp=us}}, dry melting conditions are reached and melting increases substantially. This dehydrates the remaining solid rock and is likely the origin of the chemically depleted lithosphere.{{sfn|Hirschmann|2010}}{{sfn|Karato|2012}}