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The concept of flipping of subduction polarity

There are two basic units consisting of subduction zone. They are overriding plate and the subduction plate[1]. Two plates move towards each other due to tectonic forces[1]. The overriding plate with lower density will be on the top of subducting plate[1]. This type of tectonic interaction is commonly found in many plate boundaries[1].

However, some scientists propose that the roles of overriding plate and subducting plate are not stationary[2]. Their roles will swap, which means the plate originally subducting beneath will become the overriding plate[2]. This phenomenon is called subduction switched[3], the flipping of subduction polarity[4] or subduction polarity reversal[2].

Examples of location of subdcution system have been identified by subduction polarity reversal:

- Caledonides, Ireland[5]

- Alps-Apennines, Italy[6][7]

- Kamchatka, Russian[8]

- Wetar, eastern Indonesia[9]

- Timor, east Savu Sea[10]

- Mediterranean[11]

- Taiwan[12][4][6]

Background[edit]

The phenomenon of subduction polarity reversal have been identified in the collision of an intra-oceanic subduction system[13], which is the collision of two oceanic plates with density contrast[1] . When two oceanic plates migrate towards each other, The oceanic plates with higher density subducts beneath and the other one overrides the down-warding plate[1]. The process continues until a buoyant continental margin sitting on the top of subducting plate was introduced into the down-going slab[14][2]. The subudction of slab will become slower and even cease[14][2]. Scientists proposed various possible models to predict what will be the next step when the intra-oceanic subduction system with the involvement of buoyant continental crust[14][2]. One of the possible consequences is the subduction polarity reversal[12][14][15][16][17][18].

Models of subduction polartiy reversal[edit]

Even through the scientists proposed the coming event after the involvement of buoyant continental crusts is subduction polarity reversal, they have different opinions towards the mechanisms leading to the change of subduction direction. Thus, there is no single models to represent subduction polarity reversal. How scientists developing the models highly depending on the parameters they focus[1].Some geologists attempt to construct the models of subduction reversal by laboratory experiments[2][16][15] or numerical modelling[17][12][19]. There are three generally-accepted models which are slab break-off model, lithoshperic break-up model and .

The models of Slab- break up are based observations by geologists, and the lithospheric break-up is based on the experiment simulation.

Slab break-off[edit]

This model was developed by analyzing the geological cross section along the collision between Eurasian plate and the Philippine plate, where is the location of an ongoing fillping of subduction polarity[4].

When two oceanic plates migrate towards each other, one plate overrides another forming subduction system. Later, a less dense, buoyant passive continental margin being introduced into this system will therefore cause the cessation of subduction system[4]. On one hand, the buoyant plate resists subduction beneath the overriding plate[4]. On the other hand, the dense oceanic slab at the subducting plate prefers to move downward[4]. This opposite forces will generate a tensile force or gravitational instability on the downward slab and lead to the break-off of the slab[19]. The space where the break-off slab creates will form mantle window[4]. Subsequently, the less dense continental margin forms the overriding plate, while the oceanic plate becomes the subducting slab[4]. The direction of subduction system changes since the break-off of slab create the space, which is the major parameter of this model[4].

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

Double convergence model[edit]

This model is developed based on the geological evolution of Alpine and Apennine subduction[20]

Similarly, two oceanic plates move towards each other. Subducting process ceases with the involvement of buoyant continental block. A new slab at the overriding plate owing to the regional compression and the density contrast of the continental block and oceanic plate[20]. Orogenic wedge is being built[20]. However, there is an obvious space problem that how to accommodate two slab. The solution is the newly- developing slab moves not only vertically but also laterally leading to a deep strike-slip movement[20]. The development of co-existence of two opposite slabs is described as a double sided subduction[21] or doubly convergent wedge[20] . Eventually, the development of new slab grows and slides on the old slab. The old slab was broken and the orogenic wedge collapses. The new slab stops the lateral motion and subducts beneath[20]. The direction of subduction system changes.

Evolution of doubly convergence model: Brown colour represents the Continental plate; White colour represents the oceanic plate; 1. 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; 4. New slab moves further downward; 5. The old slab breaks off; 6. The new slab subducts beneath.

Lithospheric break-up[edit]

The lithospheric break-up model is simulated by hydrocarbon experiments in the laboratory[2]. The reserachers set up the setting of subduction zone which are analogized hydrocarbon with different viscosity representing various layers in subdcution zone[2].

The initial setting of the simulated subdcution zone model is confined by two pistons. The piston connected to the overriding plate is locked, while the piston linking to subducting plate is applied a constant rate of compression[2]. More importantly, there are a relative thin magmatic arc and pre-existing fault dipping towards the subducting plate at the overriding plate[2]. The detachment of pre-existing fault occurs when buoyant continental margin is in contact with the overriding plate[2]. It is because the buoyant margin resists to subduct and significantly increases the frictional force in the contact region[2]. The subduction then stops. Subsequently, the new subducting slab develops at overriding plate with the continuous compression[2]. The new developing slab eventually penetrates and breaks the old slab[2]. A new subdcution is developed with an opposite direction of the previous one[2].

In reality, the magmatic arc is relatively weak zone at the overriding plate because it has s thin lithosphere and is further weaken by high heat flow[22][23] and hydro thermal fluid[24][25] . Pre-existing fault in this simulation is also common the magmatic arc [26]. This experiment is successful analogy to subduction polarity reversal happened at Kamchatka in early Eocene[27][8] and the active example at Taiwan region[2] [28]as well as at Timor [29][30].

A. Chemenda's Experiment setup of lithoshperic 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.
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 slabe breaks the old slab

Summary[edit]

The criteria of having subduction polarity reversal

  1. Intra-oceanic subduction system with a buoyant continental plate
  2. Subduction system ceases with the involvement of continental plate
  3. Old slab breaks off

Different models represeting the subduction polarity reversal depends highly on parameters the scientists considered. Here is the summary table showing the comparison models.

Difference Slab break-off Double convergence Lithospheric break-up
Reasons of slab break-off Tensile force at the old slab Lateral sliding by the new slab Pre-existing fault leads to penetration of new slab
Accommodation of new slab Mantle window A deep strike-slip movement Penetration of new slab breaks of the old slab

Taiwan as an active example of subduction polarity reversal[edit]

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 of flat plain such as Ilan Plain and Pingtung Plain[31], while the southern part of Taiwan is concentrated with many high mountains like Kushan reaching about 3950m. This huge difference in topographies is the consequence of the flipping of subduction polarity[32]. Most of models studying this phenomenon will focus on an active collision in Taiwan which appears to reveal the incipient stages of subduction reversal[12][14][15][16][17][18].

The collision of N- trending Luzon arc in Philippine Sea plate (PP) with E-trending Eurasian plate (EP) started at mid-Miocene[32] forming an intra-oceanic subduction system [13][33]. Taiwan was formed by this process. The south-north dichotomy in Taiwan is like a story book telling the evolution in subduction zone. The Philippine Sea plate subducts into Eurasian plate at south-west part of WEP (Western edge of north-dipping Philippine Sea Plate) [32] , and the latter overrides the former at north east part of WEP [32] .The collision between two plates started at the Northern Taiwan and propagated towards south with 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 [34].

1) Cross-section A-A’ [35] (Post-collision): The passive continental margin of Eurasian plate, a buoyant continental crust, overrides the Philippine sea plate .The Eurasian plate is receiving lithospheric stretching forming Okinawa Trough.

2) Cross-section B-B’ [35]: The Philippine Sea Plate subducts beneath the Eurasian plate,and Ryukyu trench roll-back leads to the extensional collapse of Taiwan orogenic wedge[36]. The direction of subduction changes in cross-section C-C'.

3) Cross-section C-C’ [35]: Drastic collision between two plate creates accretionary wedge and develops orogenic belt. Taiwan orogens reached the maximum height with an equal amount of erosion and growth rate.[37].The angle of the slab is almost 80 degrees dipping downward [38].

4) Cross-section D-D’ [35]: The Eurasian plate is actively subducting into the Philippine Sea plate at 80mm/year along Manila Trench[36]. 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 steeped as cross-section C-C' [38].The accretionary wedge was just developed.

5) Cross-section E-E’ [35](Pre-Collision): Slab penetrates beneath the Philippine Sea plate and brings hydrous materials to generate a mantle wedge[35] and Luzon volcanic arc.

See also[edit]

Geology of Taiwan

References[edit]

  1. ^ a b c d e f g Arc-Continent Collision | Dennis Brown | Springer.
  2. ^ a b c d e f g h i j k l m n o p q Chemenda, A. I.; Yang, R. -K.; Stephan, J. -F.; Konstantinovskaya, E. A.; Ivanov, G. M. (2001-04-10). "New results from physical modelling of arc–continent collision in Taiwan: evolutionary model". Tectonophysics. 333 (1–2): 159–178. doi:10.1016/S0040-1951(00)00273-0.
  3. ^ Willett, S. D., & Beaumont, C. (1994). Subduction of Asian lithospheric mantle beneath Tibet inferred from models of continental collision. Nature, 369(6482), 642-645.
  4. ^ a b c d e f g h i Teng, Louis S.; Lee, C. T.; Tsai, Y. B.; Hsiao, Li-Yuan (2000-02-01). "Slab breakoff as a mechanism for flipping of subduction polarity in Taiwan". Geology. 28 (2): 155–158. doi:10.1130/0091-7613(2000)282.0.CO;2. ISSN 0091-7613.
  5. ^ Ryan, P. D.; Dewey, J. F. (2011-01-01). Arc-Continent Collision. Frontiers in Earth Sciences. Springer Berlin Heidelberg. pp. 373–401. doi:10.1007/978-3-540-88558-0_13. ISBN 9783540885573.
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  9. ^ Hamilton, Warren Bell; Pertambangan, Indonesia Departemen; Development, United States Agency for International (1979-01-01). Tectonics of the Indonesian region. U.S. Govt. Print. Off.
  10. ^ McCaffrey, Robert; Molnar, Peter; Roecker, Steven W.; Joyodiwiryo, Yoko S. (1985-05-10). "Microearthquake seismicity and fault plane solutions related to arc-continent collision in the Eastern Sunda Arc, Indonesia". Journal of Geophysical Research: Solid Earth. 90 (B6): 4511–4528. doi:10.1029/JB090iB06p04511. ISSN 2156-2202.
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  24. ^ Arcay, D.; Doin, M.-P.; Tric, E.; Bousquet, R.; de Capitani, C. (2006-02-01). "Overriding plate thinning in subduction zones: Localized convection induced by slab dehydration". Geochemistry, Geophysics, Geosystems. 7 (2): Q02007. doi:10.1029/2005GC001061. ISSN 1525-2027.
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  26. ^ Toth, John; Gurnis, Michael (1998-08-10). "Dynamics of subduction initiation at preexisting fault zones". Journal of Geophysical Research: Solid Earth. 103 (B8): 18053–18067. doi:10.1029/98JB01076. ISSN 2156-2202.
  27. ^ Konstantinovskaia, Elena A (2000-10-15). "Geodynamics of an Early Eocene arc–continent collision reconstructed from the Kamchatka Orogenic Belt, NE Russia". Tectonophysics. 325 (1–2): 87–105. doi:10.1016/S0040-1951(00)00132-3.
  28. ^ Chemenda, A. I.; Yang, R. K.; Hsieh, C. -H.; Groholsky, A. L. (1997-06-15). "Evolutionary model for the Taiwan collision based on physical modelling". Tectonophysics. An Introduction to Active Collision in Taiwan. 274 (1): 253–274. doi:10.1016/S0040-1951(97)00025-5.
  29. ^ 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.
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  31. ^ Angelier, Jacques; Chang, Tsui-Yü; Hu, Jyr-Ching; Chang, Chung-Pai; Siame, Lionel; Lee, Jian-Cheng; Deffontaines, Benoît; Chu, Hao-Tsu; Lu, Chia-Yü (2009-03-10). "Does extrusion occur at both tips of the Taiwan collision belt? Insights from active deformation studies in the Ilan Plain and Pingtung Plain regions". Tectonophysics. Geodynamics and active tectonics in East Asia. 466 (3–4): 356–376. doi:10.1016/j.tecto.2007.11.015.
  32. ^ a b c d Teng, Louis S.; Lee, C. T.; Tsai, Y. B.; Hsiao, Li-Yuan (2000-02-01). "Slab breakoff as a mechanism for flipping of subduction polarity in Taiwan". Geology. 28 (2): 155–158. doi:10.1130/0091-7613(2000)282.0.CO;2. ISSN 0091-7613.
  33. ^ Leat, P. T.; Larter, R. D. (2003-01-01). "Intra-oceanic subduction systems: introduction". Geological Society, London, Special Publications. 219 (1): 1–17. doi:10.1144/GSL.SP.2003.219.01.01. ISSN 0305-8719.
  34. ^ Van Avendonk, Harm J. A.; McIntosh, Kirk D.; Kuo-Chen, Hao; Lavier, Luc L.; Okaya, David A.; Wu, Francis T.; Wang, Chien-Ying; Lee, Chao-Shing; Liu, Char-Shine (2016-01-01). "A lithospheric profile across northern Taiwan: from arc-continent collision to extension". Geophysical Journal International. 204 (1): 331–346. doi:10.1093/gji/ggv468. ISSN 0956-540X. {{cite journal}}: no-break space character in |last= at position 4 (help)
  35. ^ a b c d e f Teng, Louis S.; Lee, C. T.; Tsai, Y. B.; Hsiao, Li-Yuan (2000-02-01). "Slab breakoff as a mechanism for flipping of subduction polarity in Taiwan". Geology. 28 (2): 155–158. doi:10.1130/0091-7613(2000)282.0.CO;2. ISSN 0091-7613.
  36. ^ a b Angelier, Jacques; Chang, Tsui-Yü; Hu, Jyr-Ching; Chang, Chung-Pai; Siame, Lionel; Lee, Jian-Cheng; Deffontaines, Benoît; Chu, Hao-Tsu; Lu, Chia-Yü (2009-03-10). "Does extrusion occur at both tips of the Taiwan collision belt? Insights from active deformation studies in the Ilan Plain and Pingtung Plain regions". Tectonophysics. Geodynamics and active tectonics in East Asia. 466 (3–4): 356–376. doi:10.1016/j.tecto.2007.11.015.
  37. ^ Suppe, J. (1984). "Kinematics of arc-continent collision, flipping of subduction, and backarc spreading near Taiwan" (PDF). Mem. Geol. Soc. China. 6(21), V33.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  38. ^ a b Ustaszewski, Kamil; Wu, Yih-Min; Suppe, John; Huang, Hsin-Hua; Chang, Chien-Hsin; Carena, Sara (2012-11-20). "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". Tectonophysics. Geodynamics and Environment in East Asia. 578: 31–49. doi:10.1016/j.tecto.2011.12.029.
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