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[[File:Subduction_polarity_reversal.svg|thumb|471x471px|The concept of flipping of subduction polarity]]
'''Subduction polarity reversal''' is a geologic process in which two converging plates switch roles: The over-lying plate becomes the down-going plate, and vice versa. There are two basic units which make up a [[Subduction|subduction zone]]. This consists of an overriding plate and the subduction plate.<ref name=":142">{{Cite book|url=httphttps://www.springer.com/gp/book/9783540885573|title=Arc-Continent Collision {{!}} Dennis Brown {{!}} Springer|isbn=9783540885573|publisher=Springer|year=2011|series=Frontiers in Earth Sciences}}</ref> Two plates move towards each other due to [[Tectonics|tectonic forces]].<ref name=":142" /> The overriding plate will be on the top of the subducting plate.<ref name=":142" /> This type of tectonic interaction is commonly found inat many [[Plate tectonics|plate boundaries]].<ref name=":142" />
However, some Geologistsgeologists propose that the roles of the overriding plate and subducting plate do not remain the same infinitelyindefinitely.<ref name=":113">{{Cite journal|lastlast1=Chemenda|firstfirst1=A. I.|last2=Yang|first2=R. -K.|last3=Stephan|first3=J. -F.|last4=Konstantinovskaya|first4=E. A.|last5=Ivanov|first5=G. M.|date=2001-04-10|title=New results from physical modelling of arc–continent collision in Taiwan: evolutionary model|url=http://www.sciencedirect.com/science/article/pii/S0040195100002730|journal=Tectonophysics|volume=333|issue=1–2|pages=159–178|doi=10.1016/S0040-1951(00)00273-0|bibcode=2001Tectp.333..159C}}</ref> Their roles will swap, which means the plate originally subducting beneath will become the overriding plate.<ref name=":113" /> This phenomenon is called '''subduction switch''',<ref>Willett,{{cite journal|last1=Willett|first1=S. D., & |last2=Beaumont, |first2=C. (1994). |title=Subduction of Asian lithospheric mantle beneath Tibet inferred frominferredfrom models of continental collision. ''|journal=Nature'', ''|date=1994-06-23|volume=369''(|issue=6482), 642-645|pages=642–645|doi=10.1038/369642a0|bibcode=1994Natur.369..642W|s2cid=4239739}}</ref> '''the flipping of subduction polarity'''<ref name=":132222">{{Cite journal|lastlast1=Teng|firstfirst1=Louis S.|last2=Lee|first2=C. T.|last3=Tsai|first3=Y. B.|last4=Hsiao|first4=Li-Yuan|date=2000-02-01|title=Slab breakoff as a mechanism for flipping of subduction polarity in Taiwan|url=http://geology.gsapubs.org/content/28/2/155|journal=Geology|language=en|volume=28|issue=2|pages=155–158|doi=10.1130/0091-7613(2000)28228<155:sbaamf>2.0.COco;2|bibcode=2000Geo....28..155T |issn=0091-7613|url=http://ntur.lib.ntu.edu.tw//handle/246246/172449 |url-access=subscription}}</ref> or '''subduction polarity reversal'''.<ref name=":113" />
Examples of subduction systems with subduction polarity reversal are:
* [[Caledonian orogeny|Caledonides]], Ireland<ref>{{Cite book|url=http://link.springer.com/chapter/10.1007/978-3-540-88558-0_13|title=Arc-Continent Collision|lastlast1=Ryan|firstfirst1=P. D.|last2=Dewey|first2=J. F.|chapter=Arc–Continent Collision in the Ordovician of Western Ireland: Stratigraphic, Structural and Metamorphic Evolution |date=2011-01-01|publisher=Springer Berlin Heidelberg|isbn=9783540885573|series=Frontiers in Earth Sciences|pages=373–401|language=en|doi=10.1007/978-3-540-88558-0_13}}</ref>
* [[Apennine Mountains|Alps-Apennines]], Italy<ref name=":43">{{Cite journal|lastlast1=Molli|firstfirst1=G.|last2=Malavieille|first2=J.|date=2010-09-28|title=Orogenic processes and the Corsica/Apennines geodynamic evolution: insights from Taiwan|url=http://link.springer.com/article/10.1007/s00531-010-0598-y|journal=International Journal of Earth Sciences|language=en|volume=100|issue=5|pages=1207–1224|doi=10.1007/s00531-010-0598-y|issn=1437-3254|bibcode=2011IJEaS.100.1207M|s2cid=129517282}}</ref><ref name=":43"/>
* [[Kamchatka Peninsula|Kamchatka]], RussianRussia<ref name=":54">{{Cite journal|last=Konstantinovskaia|first=E. A|date=2001-04-10|title=Arc–continent collision and subduction reversal in the Cenozoic evolution of the Northwest Pacific: an example from Kamchatka (NE Russia)|url=http://www.sciencedirect.com/science/article/pii/S0040195100002687|journal=Tectonophysics|volume=333|issue=1–2|pages=75–94|doi=10.1016/S0040-1951(00)00268-7|bibcode=2001Tectp.333...75K}}</ref>
* [[Wetar]], eastern Indonesia<ref>{{Cite book|url=https://books.google.com/books?hl=en&lr=&id=bKg_AAAAIAAJ&oi=fnd&pg=PR1&dq=Tectonics+of+the+Indonesian+region&otspg=SQ2w7f3RXL&sig=tlwelNMpk0N1XqP6KdXcJY_HMk4&redir_esc=y#v=onepage&q=Tectonics%20of%20the%20Indonesian%20region&f=falsePR1|title=Tectonics of the Indonesian region|lastlast1=Hamilton|firstfirst1=Warren Bell|last2=Pertambangan|first2=Indonesia Departemen|last3=Development|first3=United States Agency for International|date=1979-01-01|publisher=U.S. Govt. Print. Off.|language=en}}</ref>
* [[Timor]], east Savu Sea<ref>{{Cite journal|lastlast1=McCaffrey|firstfirst1=Robert|last2=Molnar|first2=Peter|last3=Roecker|first3=Steven W.|last4=Joyodiwiryo|first4=Yoko S.|date=1985-05-10|title=Microearthquake seismicity and fault plane solutions related to arc-continent collision in the Eastern Sunda Arc, Indonesia|url=http://onlinelibrary.wiley.com/doi/10.1029/JB090iB06p04511/abstract|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=90|issue=B6|pages=4511–4528|doi=10.1029/JB090iB06p04511|issn=2156-2202|bibcode=1985JGR....90.4511M|s2cid=130977948}}</ref>
* [[Mediterranean Sea|Mediterranean]]<ref>{{Cite journal|title=Structure and dynamics of subducted lithosphere in the Mediterranean region|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=4305568|journal=Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen|volume=95|issue=3|issn=0924-8323}}</ref>
* [[Geology of Taiwan|Taiwan]]<ref name=":132222"/><ref name=":43" /><ref name=":03">{{Cite journal|lastlast1=Chemenda|firstfirst1=A. I.|last2=Yang|first2=R. K.|last3=Hsieh|first3=C. -H.|last4=Groholsky|first4=A. L.|date=1997-06-15|title=Evolutionary model for the Taiwan collision based on physical modelling|url=http://www.sciencedirect.com/science/article/pii/S0040195197000255|journal=Tectonophysics|series=An Introduction to Active Collision in Taiwan|volume=274|issue=1|pages=253–274|doi=10.1016/S0040-1951(97)00025-5|bibcode=1997Tectp.274..253C}}</ref>
== Background ==
The phenomenon of subduction polarity reversal has been identified in the collision of an intra-oceanic subduction system,<ref name=":322">{{Cite journal|lastlast1=Clift|firstfirst1=Peter D.|last2=Schouten|first2=Hans|last3=Draut|first3=Amy E.|date=2003-01-01|title=A general model of arc-continent collision and subduction polarity reversal from Taiwan and the Irish Caledonides|url=http://sp.lyellcollection.org/content/219/1/81|journal=Geological Society, London, Special Publications|language=en|volume=219|issue=1|pages=81–98|doi=10.1144/GSL.SP.2003.219.01.04|issn=0305-8719|bibcode=2003GSLSP.219...81C|s2cid=130378801|url-access=subscription}}</ref> which is the collision of two [[Oceanic crust|oceanic plates]].<ref name=":142" /> When two oceanic plates migrate towards each other, one subducts below the other. Generally, the oceanic plate with higher density subducts beneath and the other one overrides the down-going slab.<ref name=":142" /> The process continues until a buoyant [[continental margin]] sitting on the top of the subducting plate is introduced into the down-going slab.<ref name=":113" /><ref name=":132222" /> The subduction of the slab becomes slower and may even cease.<ref name=":113" /><ref name=":132222" /> Geologists propose various possible models to predict what will be the next step for the intra-oceanic subduction system with the involvement of buoyant [[continental crust]].<ref name=":113" /><ref name=":132222"/> One of the possible results is subduction polarity reversal.<ref name=":132222"/><ref name=":03" /><ref name=":322"/><ref name=":23">{{Cite journal|lastlast1=Lallemand|firstfirst1=Serge|last2=Font|first2=Yvonne|last3=Bijwaard|first3=Harmen|last4=Kao|first4=Honn|date=2001-07-10|title=New insights on 3-D plates interaction near Taiwan from tomography and tectonic implications|url=http://www.sciencedirect.com/science/article/pii/S0040195101000713|journal=Tectonophysics|volume=335|issue=3–4|pages=229–253|doi=10.1016/S0040-1951(01)00071-3|bibcode=2001Tectp.335..229L}}</ref><ref name=":73">{{Cite journal|lastlast1=Baes|firstfirst1=Marzieh|last2=Govers|first2=Rob|last3=Wortel|first3=Rinus|author-link3=Rinus Wortel|date=2011-12-01|title=Switching between alternative responses of the lithosphere to continental collision|url=http://gji.oxfordjournals.org/content/187/3/1151|journal=Geophysical Journal International|language=en|volume=187|issue=3|pages=1151–1174|doi=10.1111/j.1365-246X.2011.05236.x|issn=0956-540X|bibcode=2011GeoJI.187.1151B|doi-access=free}}</ref><ref name=":93">{{Cite journal|last=Seno|first=Tetsuzo|date=1977-10-20|title=The instantaneous rotation vector of the Philippine sea plate relative to the Eurasian plate|url=http://www.sciencedirect.com/science/article/pii/0040195177901688|journal=Tectonophysics|volume=42|issue=2|pages=209–226|doi=10.1016/0040-1951(77)90168-8|bibcode=1977Tectp..42..209S}}</ref>
== Models of subduction polarity reversal ==
Even though many geologists agree that after the involvement of buoyant [[continental crust]], subduction polarity reversal may occur, they have different opinions towards the mechanisms leading to the change of subduction direction. Thus, there is no single model to represent subduction polarity reversal. How geologists develop the models depends on the parameters they focus on.<ref name=":142" /> Some geologists attempt to construct models of subduction reversal bythrough laboratory experiments<ref name=":113" /><ref name=":322"/><ref name=":23" /> or observations.<ref name=":132222"/><ref name=":103" /> There are three common models: [[#Slab break-offdetachment|slab break-off]],<ref name=":132222" /> [[#Double convergence model|double convergence]]<ref name=":103"/> and [[#Lithosphere break-up|lithospheric break-up]].<ref name=":113" />
The models of slab-break up<ref name=":132222" /> and double convergence are based on observations by geologists,<ref name=":103"/> and the lithosphere break-up model is based on experimental [[simulation]].<ref name=":113" />
The criteria for having subduction polarity reversal are
=== Slab break-off ===
This model was developed by analyzing the geological cross section along the collision between [[Eurasian Plate|Eurasian plate]] and the [[Philippine Sea Plate|Philippine sea plate]], which is the ___location of an ongoing flipping of subduction polarity.<ref name=":132222"/>
When two [[Oceanic crust|oceanic plates]] migrate towards each other, one plate overrides another forming a [[Subduction|subduction system]]. Later, a light and buoyant [[Continental margin|passive continental margin]] introduced into this system will cause the cessation of [[Subduction|subduction system]].<ref name=":132222"/> On one hand, the buoyant plate resists subduction beneath the overriding plate.<ref name=":132222"/> On the other hand, the dense oceanic [[Slab (geology)|slab]] at the subducting plate prefers to move downward.<ref name=":132222"/> These opposite forces will generate a [[Tension (physics)|tensile force]] or gravitational instability on the downward [[slab]] and lead to the break-off of the slab.<ref name=":822">{{Cite book|url=https://books.google.com/books?hl=en&lr=&id=7l9KrXgOELwC&oi=fnd&pg=PR9&dq=subduction:+Insights+from+Physical+Mod-+eling.+Kluwer,+Dordrecht&ots=CrVyim6ABr&sig=5Oe0Gge72kTdliFQ6md_m065c9I&redir_esc=y#v=onepage&q=subduction:%20Insights%20from%20Physical%20Mod-%20eling.%20Kluwer,%20Dordrecht&f=false|title=Subduction: Insights from Physical Modeling|last=Shemenda|first=Alexander I.|date=1994-09-30|publisher=Springer Science & Business Media|isbn=9780792330424|language=en}}</ref> The space where the break-off slab separates will form a mantle window.<ref name=":132222"/> Subsequently, the less dense continental margin forms the overriding plate, while the oceanic plate becomes the subducting slab.<ref name=":132222"/> The direction of subduction system changes since the break-off of slab creates the space, which is the major parameter of this model.<ref name=":132222"/>
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![[File:Slab_break_model.gif|thumb|457x457px|'''The evolution diagram showing how the subduction reversal initiated by a break-off slab at subducting plate:''' Brown colour is the less dense continental crusts; White colour is the oceanic crust; 1. Two plates move towards each other; 2. The buoyant continental crust resists to subduct; 3. Mantle window is created by gravitational instability; 4. New subducting plate develops]]
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=== Double convergence model ===
This model is developed based on the geological evolution of Alpine and Apennine subduction<ref name=":103">{{Cite journal|last=Vignaroli|first=Gianluca|last2=Faccenna|first2=Claudio|last3=Jolivet|first3=Laurent|last4=Piromallo|first4=Claudia|last5=Rossetti|first5=Federico|date=2008-04-01|title=Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy|url=http://www.sciencedirect.com/science/article/pii/S004019510700457X|journal=Tectonophysics|volume=450|issue=1–4|pages=34–50|doi=10.1016/j.tecto.2007.12.012}}</ref>
Similarly, two oceanic plates move towards each other. The subducting process ceases with the involvement of buoyant continental block. A new slab is formed at the overriding plate owing to the regional compression and the density contrast of the continental block and oceanic plate.<ref name=":103" /> An [[orogenic wedge]] is built.<ref name=":103" /> However, there is an obvious space problem about how to accommodate two slabs. The solution is the new developing slab moves not only vertically, but also laterally leading to a deep strike-slip movement.<ref name=":103" /> The development of co-existence of two opposite slabs is described as a double sided subduction<ref>{{Cite journal|last=Tao|first=Winston C.|last2=O'connell|first2=Richard J.|date=1992-06-10|title=Ablative subduction: A two-sided alternative to the conventional subduction model|url=http://onlinelibrary.wiley.com/doi/10.1029/91JB02422/abstract|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=97|issue=B6|pages=8877–8904|doi=10.1029/91JB02422|issn=2156-2202}}</ref> or doubly convergent wedge.<ref name=":103" /> Eventually, the development of new slab grows and slides onto the old slab. The old slab breaks off and the orogenic wedge collapses. The new slab stops the lateral motion and subducts beneath.<ref name=":103" /> The direction of subduction system changes.<ref name=":103" />
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![[File:Doubly_Convergence.gif|thumb|457x457px|Evolution of doubly convergence model: Brown colour represents the Continental plate; White colour represents the oceanic plate; C1. The plate with both continental and oceanic plate subducts beneath; 2. The continental block engage in the subduction with budiling orogenic wedge; 3. The new slab develop and two slabs exhibit a deep strike-slip movement (Double circle means pointing out of the screen; Cross inside the circle means pointing into the screen; 4. New slab moves further downward; 5. The old slab breaks off; 6. The new slab subducts beneath.]]
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=== Lithosphere break-up ===
The lithosphere break-up model is simulated by hydrocarbon experiments in the laboratory.<ref name=":113" /> The researchers set up the setting of subduction zone which are analogized by hydrocarbons with different densities representing various layers in the [[Subduction|subduction zone]].<ref name=":113" />
The initial setting of the simulated [[Subduction|subduction zone]] model is confined by two pistons. The piston connected to the overriding plate is locked, while the piston linking to subducting plate is subjected to a constant rate of compression.<ref name=":113" /> More importantly, there is a relatively thin [[Volcanic arc|magmatic arc]] and pre-existing fault dipping towards the subducting plate at the overriding plate.<ref name=":113" /> The detachment of the pre-existing fault occurs when buoyant [[continental margin]] is in contact with the overriding plate.<ref name=":113" /> It is because the buoyant margin resists [[subduction]] and significantly increases the [[Friction|frictional force]] in the contact region.<ref name=":113" /> The subduction then stops. Subsequently, the new subducting slab develops at an overriding plate with the continuous compression.<ref name=":113" /> The new developing slab eventually penetrates and breaks the old slab.<ref name=":113" /> A new subduction is developed with an opposite direction of the previous one.<ref name=":113" />
In reality, the magmatic arc is a relatively weak zone at the overriding plate because it has a thin lithosphere and is further weakened by high heat flow<ref>{{Cite journal|last=Currie|first=Claire A.|last2=Hyndman|first2=Roy D.|date=2006-08-01|title=The thermal structure of subduction zone back arcs|url=http://onlinelibrary.wiley.com/doi/10.1029/2005JB004024/abstract|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=111|issue=B8|pages=B08404|doi=10.1029/2005JB004024|issn=2156-2202}}</ref><ref>{{Cite journal|last=Currie|first=C. A|last2=Wang|first2=K|last3=Hyndman|first3=Roy D|last4=He|first4=Jiangheng|date=2004-06-30|title=The thermal effects of steady-state slab-driven mantle flow above a subducting plate: the Cascadia subduction zone and backarc|url=http://www.sciencedirect.com/science/article/pii/S0012821X04002687|journal=Earth and Planetary Science Letters|volume=223|issue=1–2|pages=35–48|doi=10.1016/j.epsl.2004.04.020}}</ref> and hot fluid.<ref>{{Cite journal|last=Arcay|first=D.|last2=Doin|first2=M.-P.|last3=Tric|first3=E.|last4=Bousquet|first4=R.|last5=de Capitani|first5=C.|date=2006-02-01|title=Overriding plate thinning in subduction zones: Localized convection induced by slab dehydration|url=http://onlinelibrary.wiley.com/doi/10.1029/2005GC001061/abstract|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=7|issue=2|pages=Q02007|doi=10.1029/2005GC001061|issn=1525-2027}}</ref><ref>{{Cite journal|last=Honda|first=Satoru|last2=Yoshida|first2=Takeyoshi|date=2005-01-01|title=Application of the model of small-scale convection under the island arc to the NE Honshu subduction zone|url=http://onlinelibrary.wiley.com/doi/10.1029/2004GC000785/abstract|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=6|issue=1|pages=Q01002|doi=10.1029/2004GC000785|issn=1525-2027}}</ref> Pre-existing faults in this simulation are also common in the magmatic arc.<ref>{{Cite journal|last=Toth|first=John|last2=Gurnis|first2=Michael|date=1998-08-10|title=Dynamics of subduction initiation at preexisting fault zones|url=http://onlinelibrary.wiley.com/doi/10.1029/98JB01076/abstract|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=103|issue=B8|pages=18053–18067|doi=10.1029/98JB01076|issn=2156-2202}}</ref> This experiment is a successful analogy to subduction polarity reversal happening at Kamchatka in early Eocene<ref name=":54" /><ref>{{Cite journal|last=Konstantinovskaia|first=Elena A|date=2000-10-15|title=Geodynamics of an Early Eocene arc–continent collision reconstructed from the Kamchatka Orogenic Belt, NE Russia|url=http://www.sciencedirect.com/science/article/pii/S0040195100001323|journal=Tectonophysics|volume=325|issue=1–2|pages=87–105|doi=10.1016/S0040-1951(00)00132-3}}</ref> and the active example at Taiwan region<ref name=":113" /><ref name=":03"/> as well as at Timor.<ref>Silver, E. A., Reed, D., McCaffrey, R., & Joyodiwiryo, Y. (1983). Back arc thrusting in the eastern Sunda arc, Indonesia- A consequence of arc-continent collision. ''Journal of Geophysical Research'', ''88''(B9), 7429-7448.</ref><ref>{{Cite journal|last=Snyder|first=D. B.|last2=Prasetyo|first2=H.|last3=Blundell|first3=D. J.|last4=Pigram|first4=C. J.|last5=Barber|first5=A. J.|last6=Richardson|first6=A.|last7=Tjokosaproetro|first7=S.|date=1996-02-01|title=A dual doubly vergent orogen in the Banda Arc continent-arc collision zone as observed on deep seismic reflection profiles|url=http://onlinelibrary.wiley.com/doi/10.1029/95TC02352/abstract|journal=Tectonics|language=en|volume=15|issue=1|pages=34–53|doi=10.1029/95TC02352|issn=1944-9194}}</ref>
{|
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![[File:Lithospheric_break-up_model_setup.svg|thumb|444x444px|A. Chemenda's Experiment setup of lithosphere break-up model: White colour indicates the oceanic plate ( Higher density) ; Brown colour indicates the continental plate ( Lower density) ;Green colour shows the pre-exsiting fault ; The plates represented by hydrocarbons floats at the asthenopshere represented by water.]]
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![[File:Lithoshperic_break-up.gif|thumb|444x444px|The evolution diagram showing how the subduction reversal initiated by a pre-existing fault at the overriding plate. 1: Compression pushing ; 2: New slab develops with the failure of the fault ; 3: New slab penetrates ; 4: New slab breaks the old slab]]
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== Summary ==
The criteria of having subduction polarity reversal
# Intra-oceanic subduction system with a buoyant continental plate
# Subduction system ceases with the involvement of continental plate
# Old slab breaks off<ref name=":113" /><ref name=":132222" />
In addition to the criteria for the occurrence of subduction polarity reversal, some geologists have attempted to define controls of this phenomenon’s initiation. Zhang proposes that “the plastic strength and age of the overriding oceanic plate in the arc-continent collision system control the initiation modes.” When the whole overriding oceanic plate has a small plastic strength and younger oceanic plate it prefers a “spontaneous subduction polarity reversal”.<ref>Zhang, S., & Leng, W. (2021). Subduction polarity reversal: Induced or spontaneous? Geophysical Research Letters, 48, e2021GL093201. https://doi {{Webarchive|url=https://web.archive.org/web/20130711094433/https://doi/ |date=2013-07-11 }} . org/10.1029/2021GL093201</ref> This is because the lack in plastic strength allows negative buoyancy to overcome and “spontaneously initiate” subduction. while the stronger plastic strength and older oceanic plate prefers an “induced subduction polarity reversal. This is because the stronger plastic strength in the oceanic plate, the more it will resist a “spontaneous subduction”, making it necessary for a compression induced subduction polarity reversal.
Different models representing the subduction polarity reversal depends highly on parameters the Geologists considered. Here is the summary table showing the comparison models.
{| class="wikitable"
|'''! Difference'''
!Slab break-off
!Double convergence
|Mantle window
|A deep strike-slip movement
|Penetration of new slab breaks ofoff the old slab
|}
=== Slab break-off ===
This model was developed by analyzing the geological cross section along the collision between [[Eurasian Plate|Eurasian plate]] and the [[Philippine Sea Plate|Philippine sea plate]], which is the ___location of an ongoing flipping of subduction polarity.<ref name=":132222" />
When two [[Oceanic crust|oceanic plates]] migrate towards each other, one plate overrides another forming a [[Subduction|subduction system]]. Later, a light and buoyant [[Continental margin|passive continental margin]] introduced into this system will cause the cessation of [[Subduction|subduction system]].<ref name=":132222" /> On one hand, the buoyant plate resists subduction beneath the overriding plate.<ref name=":132222" /> On the other hand, the dense oceanic [[Slab (geology)|slab]] at the subducting plate prefers to move downward.<ref name=":132222" /> These opposite forces will generate a [[Tension (physics)|tensile force]] or gravitational instability on the downward [[slab (geology)|slab]] and lead to the break-off of the slab.<ref name=":822">{{Cite book|url=https://books.google.com/books?id=7l9KrXgOELwC&dq=subduction%3A+Insights+from+Physical+Mod-+eling.+Kluwer%2C+Dordrecht&pg=PR9|title=Subduction: Insights from Physical Modeling|last=Shemenda|first=Alexander I.|date=1994-09-30|publisher=Springer Science & Business Media|isbn=9780792330424|language=en}}</ref> The space where the break-off slab separates will form a mantle window.<ref name=":132222" /> Subsequently, the less dense continental margin forms the overriding plate, while the oceanic plate becomes the subducting slab.<ref name=":132222" /> The direction of the subduction system changes since the break-off of slab creates the space, which is the major parameter of this model.<ref name=":132222" />[[File:Slab_break_model.gif|thumb|457x457px|'''The evolution diagram showing how the subduction reversal initiated by a break-off slab at subducting plate:''' Brown colour is the less dense continental crusts; White colour is the oceanic crust; 1. Two plates move towards each other; 2. The buoyant continental crust resists to subduct; 3. Mantle window is created by gravitational instability; 4. New subducting plate develops|center]]
=== Double convergence model ===
This model is developed based on the geological evolution of Alpine and Apennine subduction.<ref name=":103">{{Cite journal|last1=Vignaroli|first1=Gianluca|last2=Faccenna|first2=Claudio|last3=Jolivet|first3=Laurent|last4=Piromallo|first4=Claudia|last5=Rossetti|first5=Federico|date=2008-04-01|title=Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy|journal=Tectonophysics|volume=450|issue=1–4|pages=34–50|doi=10.1016/j.tecto.2007.12.012|bibcode=2008Tectp.450...34V}}</ref>
Similarly, two oceanic plates move towards each other. The subduction process ceases with the involvement of buoyant continental block. A new slab is formed at the overriding plate owing to the regional compression and the difference in density between the continental block and oceanic plate.<ref name=":103" /> An [[orogenic wedge]] is built.<ref name=":103" /> However, there is an obvious space problem about how to accommodate two slabs. The solution is the new developing slab moves not only vertically, but also laterally leading to a deep strike-slip movement.<ref name=":103" /> The development of co-existence of two opposite slabs is described as a double sided subduction<ref>{{Cite journal|last1=Tao|first1=Winston C.|last2=O'connell|first2=Richard J.|date=1992-06-10|title=Ablative subduction: A two-sided alternative to the conventional subduction model|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=97|issue=B6|pages=8877–8904|doi=10.1029/91JB02422|issn=2156-2202|bibcode=1992JGR....97.8877T}}</ref> or doubly convergent wedge.<ref name=":103" /> Eventually, the development of new slab grows and slides onto the old slab. The old slab breaks off and the orogenic wedge collapses. The new slab stops the lateral motion and subducts beneath.<ref name=":103" /> The direction of subduction system changes.<ref name=":103" />[[File:Doubly_Convergence.gif|thumb|457x457px|Evolution of double convergence model: Brown colour represents the Continental plate; White colour represents the oceanic plate; C1. The plate with both continental and oceanic plate subducts beneath; 2. The continental block engage in the subduction with building orogenic wedge; 3. The new slab develops and two slabs exhibit a deep strike-slip movement (Double circle means pointing out of the screen; Cross inside the circle means pointing into the screen; 4. New slab moves further downward; 5. The old slab breaks off; 6. The new slab subducts beneath.|center]]
=== Lithosphere break-up ===
The lithosphere break-up model is simulated by hydrocarbon experiments in the laboratory.<ref name=":113" /> The researchers set up the setting of subduction zone which are analogized by hydrocarbons with different densities representing various layers in the [[Subduction|subduction zone]].<ref name=":113" />
The initial setting of the simulated [[Subduction|subduction zone]] model is confined by two pistons. The piston connected to the overriding plate is locked, while the piston linking to subducting plate is subjected to a constant rate of compression.<ref name=":113" /> More importantly, there is a relatively thin [[Volcanic arc|magmatic arc]] and pre-existing fault dipping towards the subducting plate at the overriding plate.<ref name=":113" /> The detachment of the pre-existing fault occurs when buoyant [[continental margin]] is in contact with the overriding plate.<ref name=":113" /> It is because the buoyant margin resists [[subduction]] and significantly increases the [[Friction|frictional force]] in the contact region.<ref name=":113" /> The subduction then stops. Subsequently, the new subducting slab develops at an overriding plate with the continuous compression.<ref name=":113" /> The new developing slab eventually penetrates and breaks the old slab.<ref name=":113" /> A new subduction zone is formed with an opposite polarity to the previous one.<ref name=":113" />
In reality, the magmatic arc is a relatively weak zone at the overriding plate because it has a thin lithosphere and is further weakened by high heat flow<ref>{{Cite journal|last1=Currie|first1=Claire A.|last2=Hyndman|first2=Roy D.|date=2006-08-01|title=The thermal structure of subduction zone back arcs|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=111|issue=B8|pages=B08404|doi=10.1029/2005JB004024|issn=2156-2202|bibcode=2006JGRB..111.8404C|doi-access=free}}</ref><ref>{{Cite journal|last1=Currie|first1=C. A|last2=Wang|first2=K|last3=Hyndman|first3=Roy D|last4=He|first4=Jiangheng|date=2004-06-30|title=The thermal effects of steady-state slab-driven mantle flow above a subducting plate: the Cascadia subduction zone and backarc|journal=Earth and Planetary Science Letters|volume=223|issue=1–2|pages=35–48|doi=10.1016/j.epsl.2004.04.020|bibcode=2004E&PSL.223...35C}}</ref> and hot fluid.<ref>{{Cite journal|last1=Arcay|first1=D.|last2=Doin|first2=M.-P.|last3=Tric|first3=E.|last4=Bousquet|first4=R.|last5=de Capitani|first5=C.|date=2006-02-01|title=Overriding plate thinning in subduction zones: Localized convection induced by slab dehydration|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=7|issue=2|pages=Q02007|doi=10.1029/2005GC001061|issn=1525-2027|bibcode=2006GGG.....7.2007A|s2cid=135199593 |url=https://hal.archives-ouvertes.fr/hal-00407579/file/Geochem%20Geophys%20Geosyst%20-%202006%20-%20Arcay%20-%20Overriding%20plate%20thinning%20in%20subduction%20zones%20Localized%20convection%20induced%20by.pdf }}</ref><ref>{{Cite journal|last1=Honda|first1=Satoru|last2=Yoshida|first2=Takeyoshi|date=2005-01-01|title=Application of the model of small-scale convection under the island arc to the NE Honshu subduction zone|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=6|issue=1|pages=Q01002|doi=10.1029/2004GC000785|issn=1525-2027|bibcode=2005GGG.....6.1002H|s2cid=134357121 |doi-access=free}}</ref> Pre-existing faults in this simulation are also common in the magmatic arc.<ref>{{Cite journal|last1=Toth|first1=John|last2=Gurnis|first2=Michael|date=1998-08-10|title=Dynamics of subduction initiation at preexisting fault zones|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=103|issue=B8|pages=18053–18067|doi=10.1029/98JB01076|issn=2156-2202|bibcode=1998JGR...10318053T|url=https://authors.library.caltech.edu/38328/1/1998_TothGurnis_JGR.pdf|doi-access=free}}</ref> This experiment is a successful analogy to subduction polarity reversal happening at Kamchatka in early Eocene<ref name=":54" /><ref>{{Cite journal|last=Konstantinovskaia|first=Elena A|date=2000-10-15|title=Geodynamics of an Early Eocene arc–continent collision reconstructed from the Kamchatka Orogenic Belt, NE Russia|journal=Tectonophysics|volume=325|issue=1–2|pages=87–105|doi=10.1016/S0040-1951(00)00132-3|bibcode=2000Tectp.325...87K}}</ref> and the active example at Taiwan region<ref name=":113" /><ref name=":03" /> as well as at Timor.<ref>{{cite journal|last1=Silver|first1=Eli A.|last2=Reed|first2=Donald|last3=McCaffrey|first3=Robert|last4=Joyodiwiryo|first4=Yoko|title=Back arc thrusting in the Eastern Sunda Arc, Indonesia: A consequence of arc-continent collision|journal=Journal of Geophysical Research: Solid Earth|date=1983-09-10|volume=88|issue=B9|pages=7429–7448|doi=10.1029/JB088iB09p07429|bibcode=1983JGR....88.7429S}}</ref><ref>{{Cite journal|last1=Snyder|first1=D. B.|last2=Prasetyo|first2=H.|last3=Blundell|first3=D. J.|last4=Pigram|first4=C. J.|last5=Barber|first5=A. J.|last6=Richardson|first6=A.|last7=Tjokosaproetro|first7=S.|date=1996-02-01|title=A dual doubly vergent orogen in the Banda Arc continent-arc collision zone as observed on deep seismic reflection profiles|journal=Tectonics|language=en|volume=15|issue=1|pages=34–53|doi=10.1029/95TC02352|issn=1944-9194|bibcode=1996Tecto..15...34S}}</ref>
[[File:Lithospheric_break-up_model_setup.svg|thumb|444x444px|A. Chemenda's Experiment setup of lithosphere break-up model: White colour indicates the oceanic plate ( Higher density); Brown colour indicates the continental plate ( Lower density);Green colour shows the pre-existing fault; The plates represented by hydrocarbons floats at the asthenosphere represented by water.|center]][[File:Lithoshperic_break-up.gif|thumb|444x444px|The evolution diagram showing how the subduction reversal initiated by a pre-existing fault at the overriding plate. 1: Compression pushing; 2: New slab develops with the failure of the fault; 3: New slab penetrates; 4: New slab breaks the old slab|center]]
== Taiwan as an active example of flipping of subduction reversal ==
[[File:Taiwan_222222.jpg|thumb|382x382px|Map of Taiwan shows the ___location of geological cross-section and the major subuductions]]
A sharp contrast of landforms in Taiwan lures many people to investigate. The northern part of Taiwan has lots ofmany flat plains such as Ilan Plain and Pingtung Plain,<ref name=":52222">{{Cite journal|lastlast1=Angelier|firstfirst1=Jacques|last2=Chang|first2=Tsui-Yü|last3=Hu|first3=Jyr-Ching|last4=Chang|first4=Chung-Pai|last5=Siame|first5=Lionel|last6=Lee|first6=Jian-Cheng|last7=Deffontaines|first7=Benoît|last8=Chu|first8=Hao-Tsu|last9=Lu|first9=Chia-Yü|date=2009-03-10|title=Does extrusion occur at both tips of the Taiwan collision belt? Insights from active deformation studies in the Ilan Plain and Pingtung Plain regions|url=http://www.sciencedirect.com/science/article/pii/S0040195107003617|journal=Tectonophysics|series=Geodynamics and active tectonics in East Asia|volume=466|issue=3–4|pages=356–376|doi=10.1016/j.tecto.2007.11.015|bibcode=2009Tectp.466..356A|url=http://ntur.lib.ntu.edu.tw//handle/246246/172548 |url-access=subscription}}</ref> while the southern part of Taiwan is concentrated with many high mountains like Kushan[[Yushan (mountain)|Yushan]] reaching about 3950m. This huge difference in topographiestopography is the consequence of '''the flipping of subduction polarity'''.<ref name=":132222"/> Most of models studying this phenomenon will focus on an active collision in Taiwan which appears to reveal the incipient stages of subduction reversal.<ref name=":132222"/><ref name=":03" /><ref name=":322"/><ref name=":23" /><ref name=":73" /><ref name=":93" />
The collision of N- trending Luzon arc in [[Philippine Sea Plate|Philippine Sea plate]] (PP) with E-trending [[Eurasian Plate|Eurasian plate]] (EP) started at mid-Miocene<ref name=":132222"/> forming an intra-oceanic subduction system.<ref name=":322" /><ref>{{Cite journal|lastlast1=Leat|firstfirst1=P. T.|last2=Larter|first2=R. D.|date=2003-01-01|title=Intra-oceanic subduction systems: introduction|url=http://sp.lyellcollection.org/content/219/1/1|journal=Geological Society, London, Special Publications|language=en|volume=219|issue=1|pages=1–17|doi=10.1144/GSL.SP.2003.219.01.01|issn=0305-8719|bibcode=2003GSLSP.219....1L|s2cid=131046715|url-access=subscription}}</ref> Taiwan was formed by this process. The south-northsouth–north topographic difference in Taiwan is like a story book telling the evolution in subduction zone. The [[Philippine Sea Plate|Philippine Sea plate]] subducts below the [[Eurasian Plate|Eurasian plate]] at south-west part of WEP (Western edge of north-dipping Philippine Sea Plate),<ref name=":132222"/> and the latter overrides the former at north east part of WEP.<ref name=":132222"/> The collision between two plates started at the Northern Taiwan and propagated south with the younger region at the southern part. Each incipient stage of subduction reversal process could be studied by correlating cross-sections in various parts of Taiwan.<ref>{{Cite journal|lastlast1=Van Avendonk|firstfirst1=Harm J. A.|last2=McIntosh|first2=Kirk D.|last3=Kuo-Chen|first3=Hao|last4=Lavier|first4=Luc L.|last5=Okaya|first5=David A.|last6=Wu|first6=Francis T.|last7=Wang|first7=Chien-Ying|last8=Lee|first8=Chao-Shing|last9=Liu|first9=Char-Shine|date=2016-01-01|title=A lithospheric profile across northern Taiwan: from arc-continent collision to extension|url=http://gji.oxfordjournals.org/content/204/1/331|journal=Geophysical Journal International|language=en|volume=204|issue=1|pages=331–346|doi=10.1093/gji/ggv468|issn=0956-540X|bibcode=2016GeoJI.204..331V|doi-access=free}}</ref>
[[File:Taiwan_geology.jpg|thumb|center|526x526px
|'''1) Cross-section A-A’''' <ref name=":132222"/> (Post-collision): The passive continental margin of [[Eurasian Plate|Eurasian plate]], a buoyant continental crust, overrides the [[Philippine Sea Plate|Philippine sea plate]] .The Eurasian plate is receivingundergoing lithospheric stretching, forming the [[Okinawa Trough]].<br/>
'''2) Cross-section B-B’''':<ref name=":132222" /> The [[Philippine Sea Plate]] subducts beneath the [[Eurasian Plate|Eurasian plate]], and [[Ryukyu Trench|Ryukyu trench]] [[Oceanic trench#Trench rollback|roll-back]] leads to the extensional collapse of Taiwan orogenic wedge.<ref name=":52222"/> The direction of subduction changes in cross-section C-C'.<br/>
'''3) Cross-section C-C’''':<ref name=":132222" /> Drastic collision between two plate creates an accretionary wedge and develops orogenic belt. Taiwan orogens reached the maximum height with an equal amount of erosion and growth rate.<ref name=":15222">{{Cite journal|last=Suppe, J. (1984)|title=Kinematics of arc-continent collision, flipping of subduction, and backarc spreading near Taiwan|url=http://twgeoref.moeacgs.gov.tw/GipOpenWeb/imgAction?f=/1984/19840281/0021.PDF|journal=Mem. Geol. Soc. China|volumeissue=6(21), V33.|pages=21–33}}</ref> The angle of the slab is almost 80 degrees dipping downward.<ref name=":6222">{{Cite journal|lastlast1=Ustaszewski|firstfirst1=Kamil|last2=Wu|first2=Yih-Min|last3=Suppe|first3=John|last4=Huang|first4=Hsin-Hua|last5=Chang|first5=Chien-Hsin|last6=Carena|first6=Sara|date=2012-11-20|title=Crust–mantle boundaries in the Taiwan–Luzon arc-continent collision system determined from local earthquake tomography and 1D models: Implications for the mode of subduction polarity reversal|url=http://www.sciencedirect.com/science/article/pii/S0040195111005385|journal=Tectonophysics|series=Geodynamics and Environment in East Asia|volume=578|pages=31–49|doi=10.1016/j.tecto.2011.12.029|bibcode=2012Tectp.578...31U}}</ref><br/>
'''4) Cross-section D-D’''':<ref name=":132222" /> The [[Eurasian Plate|Eurasian plate]] is actively subducting into the [[Philippine Sea Plate|Philippine Sea plate]] at 80mm/year along the Manila Trench.<ref name=":52222" /> The slab is penetrating into the mantle and the volume of melt in mantle wedge keeps increasing. Meanwhile, the angle of subduction slab is not as steepedsteep as in cross-section C-C'.<ref name=":6222" /> The accretionary wedge was just developed.<br/>
'''5) Cross-section E-E’''' <ref name=":132222" />(Pre-Collision): Slab penetrates beneath the [[Philippine Sea Plate|Philippine Sea plate]] and brings hydrous materials to generate a [[mantle wedge]]<ref name=":132222" /> and [[Luzon Volcanic Arc|Luzon volcanic arc]].
]]
== See also ==
* [[Geology of Taiwan]]
* [[Subduction erosion]]
* [[Wilson cycle]]
== References ==
{{Reflist|30em}}
[[Category:Plate tectonicsSubduction]]
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