Editing Subduction (section)

===Initiation of subduction===
Although stable subduction is fairly well understood, the process by which subduction is initiated remains a matter of discussion and continuing study. Subduction can begin spontaneously if the denser oceanic lithosphere can founder and sink beneath the adjacent oceanic or continental lithosphere through vertical forcing only; alternatively, existing plate motions can induce new subduction zones by horizontally forcing the oceanic lithosphere to rupture and sink into the asthenosphere.<ref>{{cite journal | last1 = Stern | first1 = R.J. | year = 2004 | title = Subduction initiation: spontaneous and induced | journal = Earth and Planetary Science Letters | volume =  226| issue = 3–4| pages =  275–292| doi = 10.1016/j.epsl.2004.08.007 | bibcode=2004E&PSL.226..275S}}</ref><ref name="Crameri-2020">{{Cite journal |last1=Crameri |first1=Fabio |last2=Magni |first2=Valentina |last3=Domeier |first3=Mathew |last4=Shephard |first4=Grace E. |last5=Chotalia |first5=Kiran |last6=Cooper |first6=George |last7=Eakin |first7=Caroline M. |last8=Grima |first8=Antoniette Greta |last9=Gürer |first9=Derya |last10=Király |first10=Ágnes |last11=Mulyukova |first11=Elvira |date=2020-07-27 |title=A transdisciplinary and community-driven database to unravel subduction zone initiation |journal=Nature Communications |language=en |volume=11 |issue=1 |pages=3750 |doi=10.1038/s41467-020-17522-9 |issn=2041-1723 |pmc=7385650 |pmid=32719322 |bibcode=2020NatCo..11.3750C }}</ref> Both models can eventually yield self-sustaining subduction zones, as the oceanic crust is metamorphosed at great depth and becomes denser than the surrounding mantle rocks. The compilation of subduction zone initiation events back to 100 Ma suggests horizontally-forced subduction zone initiation for most modern subduction zones,<ref name="Crameri-2020" /> which is supported by results from numerical models<ref>{{cite journal | last1 = Hall | first1 = C.E. |display-authors=etal | year = 2003 | title = Catastrophic initiation of subduction following forced convergence across fracture zones | journal = Earth and Planetary Science Letters | volume =  212| issue = 1–2| pages =  15–30| doi = 10.1016/S0012-821X(03)00242-5 | bibcode=2003E&PSL.212...15H}}</ref><ref>{{cite journal | last1 = Gurnis | first1 = M. | display-authors = etal | year = 2004 | title = Evolving force balance during incipient subduction | url = http://authors.library.caltech.edu/1097/ | journal = Geochemistry, Geophysics, Geosystems | volume = 5 | issue = 7 | pages = Q07001 | doi = 10.1029/2003GC000681 | bibcode = 2004GGG.....5.7001G | s2cid = 18412472 | access-date = 2016-07-22 | archive-date = 2022-02-10 | archive-url = https://web.archive.org/web/20220210204044/http://authors.library.caltech.edu/1097/ | url-status = dead }}</ref> and geologic studies.<ref>{{cite journal |last1=Keenan |first1=Timothy E. |last2=Encarnación |first2=John |last3=Buchwaldt |first3=Robert |last4=Fernandez |first4=Dan |last5=Mattinson |first5=James |last6=Rasoazanamparany |first6=Christine |last7=Luetkemeyer |first7=P. Benjamin |title=Rapid conversion of an oceanic spreading center to a subduction zone inferred from high-precision geochronology |journal=PNAS |doi=10.1073/pnas.1609999113 |pmid=27821756 |pmc=5127376 |volume=113 |issue=47 |pages=E7359–E7366|bibcode=2016PNAS..113E7359K |year=2016 |doi-access=free }}</ref><ref>{{cite journal |last1=House |first1=M. A. |last2=Gurnis |first2=M. |last3=Kamp |first3=P. J. J. |last4=Sutherland |first4=R. |date=September 2002 |title=Uplift in the Fiordland Region, New Zealand: Implications for Incipient Subduction |journal=Science |volume=297 |issue=5589 |pages=2038–2041 |doi=10.1126/science.1075328 |pmid=12242439|bibcode=2002Sci...297.2038H |s2cid=31707224 |url=https://authors.library.caltech.edu/35819/2/1075328s.pdf }}</ref> Some [[analogue modelling (geology)|analogue modeling]] shows, however, the possibility of spontaneous subduction from inherent density differences between two plates at specific locations like passive margins and along [[transform fault]]s.<ref name="Mart">{{Cite journal |doi=10.1111/j.1365-246X.2005.02544.x |author=Mart, Y., Aharonov, E., Mulugeta, G., Ryan, W.B.F., Tentler, T., Goren, L. |year=2005 |title=Analog modeling of the initiation of subduction |journal=Geophys. J. Int. |volume=160 |pages=1081–1091 |issue=3 |bibcode = 2005GeoJI.160.1081M |doi-access=free }}</ref><ref name="Goren">{{Cite journal |author=Goren, L. |author2=E. Aharonov |author3=G. Mulugeta |author4=H. A. Koyi |author5=Y. Mart |year=2008 |title=Ductile Deformation of Passive Margins: A New Mechanism for Subduction Initiation |journal=J. Geophys. Res. |volume=113 |issue=B8 |page=B08411 |doi=10.1029/2005JB004179 |bibcode=2008JGRB..113.8411G|s2cid=130779676 |doi-access=free }}</ref> There is evidence this has taken place in the Izu-Bonin-Mariana subduction system.<ref>{{cite journal | last1 = Stern | first1 = R.J. | last2 = Bloomer | first2 = S.H. | year = 1992 | title = Subduction zone infancy: examples from the Eocene Izu-Bonin-Mariana and Jurassic California arcs | journal = Geological Society of America Bulletin | volume =  104| issue = 12| pages = 1621–1636 | doi = 10.1130/0016-7606(1992)104<1621:SZIEFT>2.3.CO;2 | bibcode = 1992GSAB..104.1621S }}</ref><ref>{{cite journal | last1 = Arculus | first1 = R.J. |display-authors=etal | year = 2015 | title = A record of spontaneous subduction initiation in the Izu–Bonin–Mariana arc | journal = Nature Geoscience | volume =  8| issue = 9| pages =  728–733| doi = 10.1038/ngeo2515 | bibcode = 2015NatGe...8..728A | hdl = 1874/330065 | s2cid = 29775269 | url = https://authors.library.caltech.edu/60310/2/ngeo2515-s1.pdf }}</ref> Earlier in Earth's history, subduction is likely to have initiated without horizontal forcing due to the lack of relative plate motion, though a proposal by A. Yin suggests that meteorite impacts may have contributed to subduction initiation on early Earth.<ref>{{cite journal | last1 = Yin | first1 = A. | year = 2012 | title = An episodic slab-rollback model for the origin of the Tharsis rise on Mars: Implications for initiation of local plate subduction and final unification of a kinematically linked global plate-tectonic network on Earth | journal = Lithosphere | volume =  4| issue = 6| pages =  553–593| doi = 10.1130/L195.1 | bibcode = 2012Lsphe...4..553Y| doi-access = free }}</ref>

Though the idea of subduction initiation at passive margins is popular, there is no modern day example for this type of subduction nucleation.<ref>{{Cite journal |last1=Stern |first1=Robert J. |last2=Gerya |first2=Taras |date=October 2018 |title=Subduction initiation in nature and models: A review |url=https://linkinghub.elsevier.com/retrieve/pii/S0040195117304390 |journal=Tectonophysics |language=en |volume=746 |pages=173–198 |doi=10.1016/j.tecto.2017.10.014|bibcode=2018Tectp.746..173S |s2cid=53970781 }}</ref> This is likely due to the strength of the oceanic or transitional crust at the continental passive margins, suggesting that if the crust did not break in its first 20 million years of life, it is unlikely to break in the future under normal sedimentation loads. Only with additional weaking of the crust, through hotspot magmatism or extensional rifting, would the crust be able to break from its continent and begin subduction.