Editing Subduction (section)

==Subduction and plate tectonics==
{{See also|Plate tectonics}}
[[File:JuandeFucasubduction.jpg|thumb|upright=1.2|The Juan de Fuca plate sinks below the North America plate at the [[Cascadia subduction zone]]]]
[[File:Oceanic spreading.svg|right|thumb|upright=1.35|The simplified model of [[mantle convection]]:<ref>Carlo Doglioni, Giuliano Panza: ''[https://core.ac.uk/download/pdf/53744253.pdf Polarized Plate Tectonics]''. Advances in Geophysics, Volume 56, 2015.</ref> Oceanic [[Plate tectonics|plates]] are subducted creating [[oceanic trench]]es.]]
According to the theory of [[plate tectonics]], the Earth's [[lithosphere]], its rigid outer shell, is broken into sixteen larger [[tectonic plates]] and several smaller plates. These plates are in slow motion, due mostly to the pull force of subducting lithosphere. Sinking lithosphere at subduction zones are a part of [[convection]] cells in the underlying ductile [[Earth's mantle|mantle]]. This process of convection allows heat generated by [[radioactive decay]] to escape from the Earth's interior.<ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=9783540436508 |pages=13–20}}</ref>

The lithosphere consists of the outermost light [[crust (geology)|crust]] plus the uppermost rigid portion of the [[Earth's mantle|mantle]]. Oceanic lithosphere ranges in thickness from just a few km for young lithosphere created at [[mid-ocean ridge]]s to around {{cvt|100|km}} for the oldest oceanic lithosphere.{{sfn|Stern|2002|p=5}} Continental lithosphere is up to {{cvt|200|km}} thick.<ref>{{cite journal |last1=Rudnick |first1=Roberta L. |last2=McDonough |first2=William F. |last3=O'Connell |first3=Richard J. |title=Thermal structure, thickness and composition of continental lithosphere |journal=Chemical Geology |date=April 1998 |volume=145 |issue=3–4 |pages=395–411 |doi=10.1016/S0009-2541(97)00151-4|bibcode=1998ChGeo.145..395R }}</ref> The lithosphere is relatively cold and rigid compared with the underlying [[asthenosphere]], and so tectonic plates move as solid bodies atop the asthenosphere. Individual plates often include both regions of the oceanic lithosphere and continental lithosphere.

Subduction zones are where cold oceanic lithosphere sinks back into the mantle and is recycled.{{sfn|Stern|2002}}<ref>{{cite journal |last1=Zheng |first1=YF |last2=Chen |first2=YX |year=2016 |title=Continental versus oceanic subduction zones |journal=National Science Review |volume=3 |issue=4 |pages=495–519 |doi=10.1093/nsr/nww049 |doi-access=free}}</ref> They are found at convergent plate boundaries, where the heavier oceanic lithosphere of one plate is overridden by the leading edge of another, less-dense plate.{{sfn|Stern|2002|p=5}} The overridden plate (the ''[[slab (geology)|slab]]'') sinks at an angle most commonly between 25 and 75 degrees to Earth's surface.<ref>{{cite journal |last1=Tovish |first1=Aaron |last2=Schubert |first2=Gerald |last3=Luyendyk |first3=Bruce P. |title=Mantle flow pressure and the angle of subduction: Non-Newtonian corner flows |journal=Journal of Geophysical Research: Solid Earth |date=10 December 1978 |volume=83 |issue=B12 |pages=5892–5898 |doi=10.1029/JB083iB12p05892 |bibcode=1978JGR....83.5892T }}</ref> This sinking is driven by the temperature difference between the slab and the surrounding asthenosphere, as the colder oceanic lithosphere is, on average, more dense.{{sfn|Stern|2002|p=5}} <!-- Sterns dismisses the importance of the eclogite transition in driving subduction.--> [[Sediments]] and some trapped water are carried downwards by the slab and recycled into the deep mantle.{{sfn|Stern|2002|p=15}}

So far, Earth is the only planet where subduction is known to occur, and subduction zones are its most important tectonic feature. Subduction is the driving force behind [[plate tectonics]], and without it, plate tectonics could not occur.{{sfn|Stern|2002|pp=1-4}} Oceanic subduction zones are located along {{Convert|55000|km|mi|abbr=on}} of convergent plate margins,<ref>{{cite book|last=Lallemand|first=S|title=La Subduction Oceanique|publisher=Gordon and Breach|location=Newark, New Jersey|year=1999|language=fr}}</ref> almost equal to the cumulative plate formation rate {{Convert|60000|km|mi|abbr=on}} of mid-ocean ridges.{{sfn|Stern|2002|p=4}}

Sea water seeps into oceanic lithosphere through fractures and pores, and reacts with minerals in the crust and mantle to form hydrous minerals (such as serpentine) that store water in their crystal structures.<ref>{{Citation |last=Frost |first=Daniel J. |title=11. The Stability of Hydrous Mantle Phases |date=2006-12-31 |url=http://dx.doi.org/10.1515/9781501509476-015 |work=Water in Nominally Anhydrous Minerals |pages=243–272 |editor1-last=Keppler |editor1-first=Hans |place=Berlin, Boston |publisher=De Gruyter |doi=10.1515/9781501509476-015 |isbn=978-1-5015-0947-6 |access-date=2021-02-27 |editor2-last=Smyth |editor2-first=Joseph R|url-access=subscription }}</ref> Water is transported into the deep mantle ''via'' hydrous minerals in subducting slabs.<ref>{{cite journal |last1=Gies |first1=Nils Benjamin |last2=Konrad-Schmolke |first2=Matthias |last3=Hermann |first3=Jörg |title=Modeling the Global Water Cycle—The Effect of Mg-Sursassite and Phase A on Deep Slab Dehydration and the Global Subduction Zone Water Budget |journal=Geochemistry, Geophysics, Geosystems |date=2024 |volume=25 |issue=3 |pages=e2024GC011507 |doi=10.1029/2024GC011507 |language=en |issn=1525-2027|doi-access=free |bibcode=2024GGG....2511507G }}</ref> During subduction, a series of minerals in these slabs such as [[Serpentinite|serpentine]] can be stable at different pressures within the slab geotherms, and may transport significant amount of water into the Earth's interior.<ref>{{Cite journal |last=Ohtani |first=Eiji |date=2015-12-15 |title=Hydrous minerals and the storage of water in the deep mantle |url=https://www.sciencedirect.com/science/article/pii/S0009254115002399 |journal=Chemical Geology |language=en |volume=418 |pages=6–15 |bibcode=2015ChGeo.418....6O |doi=10.1016/j.chemgeo.2015.05.005 |issn=0009-2541|url-access=subscription }}</ref> As plates sink and heat up, released fluids can trigger seismicity and induce melting within the subducted plate and in the overlying mantle wedge. This type of melting selectively concentrates volatiles and transports them into the overlying plate. If an eruption occurs, the cycle then returns the volatiles into the oceans and atmosphere.<ref>{{Cite journal |last1=Goes |first1=Saskia |last2=Collier |first2=Jenny |last3=Blundy |first3=Jon |last4=Davidson |first4=Jon |last5=Harmon |first5=Nick |last6=Henstock |first6=Tim |last7=Kendall |first7=J. |last8=MacPherson |first8=Colin |last9=Rietbrock |first9=Andreas |last10=Rychert |first10=Kate |last11=Prytulak |first11=Julie |last12=Van Hunen |first12=Jeroen |last13=Wilkinson |first13=Jamie |last14=Wilson |first14=Marjorie |year=2019 |title=Project VoiLA: Volatile Recycling in the Lesser Antilles |url=https://eos.org/science-updates/project-voila-the-volatile-recycling-in-the-lesser-antilles |journal=Eos |language=en-US |volume=100 |doi=10.1029/2019eo117309 |access-date=2021-02-27 |hdl-access=free |hdl=10044/1/69387 |s2cid=134704781}}</ref>