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'''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=https://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 found at many [[Plate tectonics|plate boundaries]].<ref name=":142" />
However, some geologists propose that the roles of the overriding plate and subducting plate do not remain the same indefinitely.<ref name=":113">{{Cite journal|last1=Chemenda|first1=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|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>{{cite journal|last1=Willett|first1=S. D.|last2=Beaumont|first2=C.|title=Subduction of Asian lithospheric mantle beneath Tibet inferredfrom models of continental collision|journal=Nature|date=1994-06-23|volume=369|issue=6482|pages=642–645|doi=10.1038/369642a0|bibcode=1994Natur.369..642W|s2cid=4239739}}</ref> '''the flipping of subduction polarity'''<ref name=":132222">{{Cite journal|last1=Teng|first1=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|journal=Geology|language=en|volume=28|issue=2|pages=155–158|doi=10.1130/0091-7613(2000)28<155:sbaamf>2.0.co;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:
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== Background ==
The phenomenon of subduction polarity reversal has been identified in the collision of an intra-oceanic subduction system,<ref name=":322">{{Cite journal|last1=Clift|first1=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|last1=Lallemand|first1=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|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|last1=Baes|first1=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|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|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 ==
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== 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 many flat plains such as Ilan Plain and Pingtung Plain,<ref name=":52222">{{Cite journal|last1=Angelier|first1=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|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 [[Yushan (mountain)|Yushan]] reaching about 3950m. This huge difference in topography 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|last1=Leat|first1=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–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|last1=Van Avendonk|first1=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|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
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