How to make a subduction zone on Earth

How to make a subduction zone on Earth

Subduction zones are ubiquitous features on Earth, and an integral part of plate tectonics. They are known to have a very important role in modulating climate on Earth, and are believed to have played an essential part in making the Earth’s surface habitable, a role that extends to present-day. This week, Antoniette Greta Grima writes about the ongoing debate on how subduction zones form and persist for millions of years, consuming oceanic lithosphere and transporting water and other volatiles to the Earth’s mantle.

Antoniette Greta Grima. PhD Student at Dept. of Earth Sciences, University College London, UK.

Before we can start thinking about how subduction zones form, we need to be clear on what we mean by the term subduction zone. In the most generic sense, this term has been described by White et al. (1970) as “an abruptly descending or formerly descended elongate body of lithosphere, together with an existing envelope of plate deformation”. In simple words this defines subduction zones as places where pieces of the Earth’s lithosphere bend downwards into the Earth’s interior. This definition however, does not take into account the spatio-temporal aspect of subduction zone formation. It also, does not differentiate between temporary, episodic lithosphere ‘peeling’ or ‘drips’, thought to precede the modern-day ocean plate-tectonic regime (see van Hunen and Moyen, 2012; Crameri et al., 2018; Foley, 2018, and references therein) and the rigid self-sustaining subduction, which we see on the present-day Earth (Gurnis et al., 2004).

A self-sustaining subduction zone is one where the total buried, rigid slab length extends deep into the upper mantle and is accompanied at the surface by back-arc spreading (Gurnis et al., 2004). The latter is an important surface observable indicating that the slab has overcome the resistive forces impeding its subduction and is falling quasi-vertically through the mantle. Gurnis et al. (2004) go on to say that if one or the other of these defining criteria is missing then subduction is forced rather than self-sustaining. Forced or induced subduction (Stern, 2004; Leng and Gurnis, 2011; Stern and Gerya, 2017; Baes et al., 2018) is described by Gurnis et al. (2004) as a juvenile, early stage system, that cannot be described as a fully fledged subduction zone. These forced subduction zones are characterised by incipient margins, short trench-arc distance, narrow trenches and a volcanically inactive island arc and/or trench. Furthermore, although these juvenile systems might be seismically active they will lack a well defined Benioff Zone. Examples of forced subduction include the Puysegur-Fiordland subduction along the Macquarie Ridge Complex, the Mussau Trench on the eastern boundary of the Caroline plate and the Yap Trench south of the Marianas, amongst others. On the other hand, Cenozoic (<66 Ma) subductions, shown in figure 2, are by this definition self-sustaining and mature subduction zones. These subduction zones including the Izu-Bonin-Mariana, Tonga-Kermadec and Aleutians subduction zones, are characterised by their extensive and well defined trenches (see figure 2) (Gurnis et al., 2004). However, despite their common categorization subduction zones can originate through various mechanisms and from very different tectonic settings.

Figure 1: Map the Earth’s subduction zones and tectonic plates from W.K and E.H. (2003). See how subduction zones dominate the figure.

1. How are subduction zones formed?

We know from the geological record that the formation of subduction zones is an ongoing process, with nearly half of the present day active subduction zones initiating during the Cenozoic (<66 Ma) (see Gurnis et al., 2004; Dymkova and Gerya, 2013; Crameri et al., 2018, and references therein). However, it is less clear how subduction zones originate, nucleate and propagate to pristine oceanic basins.


Figure 2: The oldest, still active subduction zones on Earth can be dated back to 66 million years ago. These are self- sustaining mature subduction zones with well defined trenches and trench lengths (modified from Gurnis et al., 2004).

Crameri et al. (2018, and references therein) list a number of mechanisms, some which are shown in figure 3, that may work together to weaken and break the lithosphere including:

  • Meteorite impact
  • Sediment loading
  • Major episode of delamination
  • Small scale convection in the sub-lithospheric mantle
  • Interaction of thermo-chemical plume with the overlying lithosphere
  • Plate bending via surface topographic variations
  • Addition of water or melt to the lithosphere
  • Pre-existing transform fault or oceanic plateau
  • Shear heating
  • Grain size reduction

Some of these mechanisms, particularly those listed at the beginning of the list are more appropriate to early Earth conditions while others, such as inherited weaknesses or fracture zones, transform faults and extinct spreading ridges are considered to be prime tectonic settings for subduction zone formation in the Cenozoic (<66 Ma) (Gurnis et al., 2004). As the oceanic lithosphere grows denser with age, it develops heterogeneity which facilitates its sinking into the mantle to form new subduction zones. However, it is important to keep in mind that without inherited, pre-existing weaknesses, it is extremely difficult to form subduction zones at passive margins. This is because as the oceanic lithosphere cools and becomes denser, it also becomes stronger and therefore harder to bend into the mantle that underlies it (Gurnis et al., 2004; Duarte et al., 2016). Gurnis et al. (2004) note that the formation of new subduction zones alters the force balance on the plate and suggest that the strength of the lithosphere during bending is potentially the largest resisting component in the development of new subduction zones. Once that resistance to bending is overcome, either through the negative buoyancy of the subducting plate and/or through the tectonic forces acting on it, a shear zone extending through the plate develops (Gurnis et al., 2004; Leng and Gurnis, 2011). This eventually leads to plate failure and subduction zone formation.

Figure 3: Different ways to form a new subduction zone (from Stern and Gerya, 2017).

2. Where can new subduction zones form?

From our knowledge of the geological record, observations of on-going subduction, and numerical modelling (Baes et al., 2011; Leng and Gurnis, 2011; Baes et al., 2018; Beaussier et al., 2018) we think that subduction zone initiation primarily occurs through the following:

In an intra-oceanic setting through surface weakening processes

An intra-oceanic setting refers to a subduction zone forming right within the oceanic plate itself. Proposed weakening mechanisms include weakening of the lithosphere due to melt and/or hydration (e.g., Crameri et al., 2018; Foley, 2018, and references therein), localised lithospheric shear heating (Thielmann and Kaus, 2012) and density variations within oceanic plate due to age heterogeneities, where its older and denser portions flounder and sink (Duarte et al., 2016). Another mechanism proposed by Baes et al. (2018) suggests that intra-oceanic subduction can also be induced by mantle suction flow. These authors suggest that mantle suction flow stemming from either slab remnants and/or from slabs of active subduction zones can act on pre-existing zones of weakness, such as STEP (subduction-transfer edge propagate) faults to trigger a new subduction zone, thus facilitating spontaneous subduction initiation (e.g. figure 3) (Stern, 2004). The Sandwich and the Tonga-Kermadec subduction zones are often cited as prime examples of intra-oceanic subduction zone formation due to mantle suction forces (Baes et al., 2018). Ueda et al. (2008) and Gerya et al. (2015) also suggest that thermochemical plumes can break the lithosphere and initiate self-sustaining subduction, provided that the overlying lithosphere is weakened through the presence of volatiles and melt (e.g. figure 3). This mechanism can explain the Venusian corona and could have facilitated the initation of plate tectonics on Earth (Ueda et al., 2008; Gerya et al., 2015). Similarly Burov and Cloetingh (2010) suggest that in the absence of plate tectonics, mantle lithospheric interaction through plume-like instabilities, can induce spontaneous downwelling of both continental and oceanic lithosphere.

Through subduction infection or invasion

Subduction invasion/infection (Waldron et al., 2014; Duarte et al., 2016) occurs when subduction migrates from an older system into a pristine oceanic basin. Waldron et al. (2014) suggest that the closure of the Iapetus Ocean is due to the encroachment of old lithosphere into a young ocean. These authors suggests that subduction initiated at the boundary between old and new oceanic lithosphere and was introduced to the area through trench rollback. This process is thought be similar to the modern day Caribbean, Scotia and Gibraltar Arcs (Duarte et al., 2016). This suggests that the older subductions of the Pacific are invading the younger Atlantic basin, which might potentially lead to collision, orogeny and closure of the Atlantic ocean (Duarte et al., 2016).

Following a subduction polarity reversal

Subduction polarity reversal describes a process where the trench jumps from the subducting plate to the overriding one, flipping its polarity in the process (see figure 3). This can result from the arrival at the trench of continental lithosphere (McKenzie, 1969) or young positively buoyant lithosphere (Crameri and Tackley, 2015). Subduction polarity reversal is often invoked to explain and justify the two juxtaposed Wadati-Benioff zones and their opposite polarities, in the Solomon Island Region (Cooper and Taylor, 1985). Indications of a polarity reversal are also exhibited below the Alpine and Apennine Belts (Vignaroli et al., 2008). Furthermore, Crameri and Tackley (2014) also suggest that the continental connection between South America and the Antarctic peninsula has been severed through a subduction polarity reversal, resulting in the lateral detachment of the South Sandwich subduction zone.

Subduction initiation at ancient/ inherited zones of lithospheric weakness

Subduction zones can also initiate at ancient, inherited zones of weakness such as old fracture zones, transform faults, extinct subduction boundaries and extinct spreading ridges (Gurnis et al., 2004). Gurnis et al. (2004) suggest that the Izu-Bonin-Mariana subduction zone initiated at a fracture zone, while the Tonga-Kermadec subduction initiated at an extinct subduction boundary. The same study also proposes that the incipient Puysegur-Fiordland subduction zone nucleated at an extinct spreading centre.

In conclusion, we can say that subduction zone formation is a complex and multi layered process that can stem from a variety of tectonic settings. However, it is clear that our planet’s current convection style, mode of surface recycling and its ability to sustain life are interlinked with subduction zone formation. Therefore, to understand better how subduction zones form is to better understand what makes the Earth the planet it is today.



Baes, M., Govers, R., and Wortel, R. (2011). Subduction initiation along the inherited weakness zone at the edge of a slab: Insights from numerical models. Geophysical Journal International, 184(3):991–1008.

Baes, M., Sobolev, S. V., and Quinteros, J. (2018). Subduction initiation in mid-ocean induced by mantle suction flow. Geophysical Journal International, 215(3):1515–1522.

Beaussier, S. J., Gerya, T. V., and Burg, J.-p. (2018). 3D numerical modelling of the Wilson cycle: structural inheritance of alternating subduction polarity. Fifty years of the Wilson Cycle concept in plate tectonics, page First published online.

Burov, E. and Cloetingh, S. (2010). Plume-like upper mantle instabilities drive subduction initiation. Geophys. Res. Lett., 37(3).

Cooper, P. and Taylor, B. (1985). Polarity reversal in the Solomon Island Arc. Nature, 313(6003):47–48.

Crameri, F., Conrad, C. P., Mont ́esi, L., and Lithgow-Bertelloni, C. R. (2018). The dynamic life of an oceanic plate. Tectonophysics.

Crameri, F. and Tackley, P. J. (2014). Spontaneous development of arcuate single-sided subduction in global 3-D mantle convection models with a free surface. Journal of Geophysical Research: Solid Earth, 119(7):5921–5942.

Crameri, F. and Tackley, P. J. (2015). Parameters controlling dynamically self-consistent plate tectonics and single-sided subduction in global models of mantle convection. Journal of Geophysical Research: Solid Earth, 3(55):1–27.

Duarte, J. C., Schellart, W. P., and Rosas, F. M. (2016). The future of Earth’s oceans: Consequences of subduction initiation in the Atlantic and implications for supercontinent formation. Geological Magazine, 155(1):45–58.

Dymkova, D. and Gerya, T. (2013). Porous fluid flow enables oceanic subduction initiation on Earth. Geophysical Research Letters, 40(21):5671–5676.

Foley, B. J. (2018). The dependence of planetary tectonics on mantle thermal state : applications to early Earth evolution. 376.

Gerya, T. V., Stern, R. J., Baes, M., Sobolev, S. V., and Whattam, S. A. (2015). Plate tectonics on the Earth triggered by plume-induced subduction initiation. Nature, 527(7577):221–225.

Gurnis, M., Hall, C., and Lavier, L. (2004). Evolving force balance during incipient subduction. Geochemistry, Geophysics, Geosystems, 5(7).

Leng, W. and Gurnis, M. (2011). Dynamics of subduction initiation with different evolutionary pathways. Geochemistry, Geophysics, Geosystems, 12(12).

McKenzie, D. P. (1969). Speculations on the Consequences and Causes of Plate Motions. Geophys. J. R. Astron. Soc., 18(1):1–32.

Stern, R. J. (2004). Subduction initiation: spontaneous and induced. Earth and Planetary Science Letters, 226(3-4):275–292.

Stern, R. J. and Gerya, T. (2017). Subduction initiation in nature and models: A review. Tectonophysics.

Thielmann, M. and Kaus, B. J. (2012). Shear heating induced lithospheric-scale localization: Does it result in subduction? Earth Planet. Sci. Lett., 359-360:1–13.

Ueda, K., Gerya, T., and Sobolev, S. V. (2008). Subduction initiation by thermal-chemical plumes: Numerical studies. Phys. Earth Planet. Inter., 171(1-4):296–312.

van Hunen, J. and Moyen, J.-F. (2012). Archean Subduction: Fact or Fiction? Annual Review of Earth and Planetary Sciences, 40(1):195–219.

Vignaroli, G., Faccenna, C., Jolivet, L., Piromallo, C., and Rossetti, F. (2008). Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy. Tectonophysics, 450(1-4):34–50.

Waldron, J. W., Schofield, D. I., Brendan Murphy, J., and Thomas, C. W. (2014). How was the iapetus ocean infected with subduction? Geology, 42(12):1095–1098.

White, D. A., Roeder, D. H., Nelson, T. H., and Crowell, J. C. (1970). Subduction. Geological Society of America Bulletin, 81(October):3431–3432.

W.K, H. and E.H., C. (2003). Earth’s Dynamic Systems. Prentice Hall; 10 edition.

Tomography and plate tectonics

Tomography and plate tectonics

The Geodynamics 101 series serves to showcase the diversity of research topics and methods in the geodynamics community in an understandable manner. We welcome all researchers – PhD students to Professors – to introduce their area of expertise in a lighthearted, entertaining manner and touch upon some of the outstanding questions and problems related to their fields. For our first ‘Geodynamics 101’ post for 2019, Assistant Prof. Jonny Wu from the University of Houston explains how to delve into the subduction record via seismic tomography and presents some fascinating 3D workflow images with which to test an identified oceanic slab. 

Jonny Wu, U. Houston

Tomography… wait, isn’t that what happens in your CAT scan? Although the general public might associate tomography with medical imaging, Earth scientists are well aware that ‘seismic tomography’ has enabled us to peer deeper, and with more clarity, into the Earth’s interior (Fig. 1). What are some of the ways we can download and display tomography to inform our scientific discoveries? Why has seismic tomography been a valuable tool for plate reconstructions? And what are some new approaches for incorporating seismic tomography within plate tectonic models?

Figure 1: Tomographic transect across the East Asian mantle under the Eurasian-South China Sea margin, the Philippine Sea and the western Pacific from Wu and Suppe (2018). The displayed tomography is the MITP08 global P-wave model (Li et al., 2008).

Downloading and displaying seismic tomography

Seismic tomography is a technique for imaging the Earth’s interior in 3-D using seismic waves. For complete beginners, IRIS (Incorporated Research Institutions for Seismology) has an excellent introduction that compares seismic tomography to medical CT scans.

A dizzying number of new, high quality seismic tomographic models are being published every year. For example, the IRIS EMC-EarthModels catalogue  currently contains 64 diverse tomographic models that cover most of the Earth, from global to regional scales. From my personal count, at least seven of these models have been added in the past half year – about one new model a month. Aside from the IRIS catalog, a plethora of other tomographic models are also publicly-available from journal data suppositories, personal webpages, or by an e-mail request to the author.

Downloading a tomographic model is just the first step. If one does not have access to custom workflows and scripts to display tomography, consider visiting an online tomography viewer. I have listed a few of these websites at the end of this blog post. Of these websites, a personal favourite of mine is the Hades Underworld Explorer built by Douwe van Hinsbergen and colleagues at Utrecht University, which uses a familiar Google Maps user interface. By simply dragging a left and right pin on the map, a user can display a global tomographic section in real time. The displayed tomographic section can be displayed in either a polar or Cartesian view and exported to a .svg file. Another tool I have found useful are tomographic ‘vote maps’, which provide indications of lower mantle slab imaging robustness by comparison of multiple tomographic models (Shephard et al., 2017). Vote maps can be downloaded from the original paper above or from the SubMachine website (Hosseini et al. (2018); see more in the website list below).

Using tomography for plate tectonic reconstructions

Tomography has played an increasing role in plate tectonic studies over the past decades. A major reason is because classical plate tectonic inputs (e.g. seafloor magnetic anomalies, palaeomagnetism, magmatism, geology) are independent from the seismological inputs for tomographic images. This means that tomography can be used to augment or test classic plate reconstructions in a relatively independent fashion. For example, classical plate tectonic models can be tested by searching tomography for slab-like anomalies below or near predicted subduction zone locations. These ‘conventional’ plate modelling workflows have challenges at convergent margins, however, when the geological record has been significantly destroyed from subduction. In these cases, the plate modeller is forced to describe details of past plate kinematics using an overly sparse geological record.

Figure 2: Tomographic plate modeling workflow proposed by Wu et al. (2016). The final plate model in c) is fully-kinematic and makes testable geological predictions for magmatic histories, terrane paleolatitudes and other geology (e.g. collisions) that can be compared against the remnant geology in d), which are relatively independent.

A ‘tomographic plate modelling’ workflow (Fig. 2) was proposed by Wu et al. (2016) that essentially reversed the conventional plate modelling workflow. In this method, slabs are mapped from tomography and unfolded (i.e. retro-deformed) (Fig. 2a). The unfolded slabs are then populated into a seafloor spreading-based global plate model. Plate motions are assigned in a hierarchical fashion depending on available kinematic constraints (Fig. 2b). The plate modelling will result in either a single unique plate reconstruction, or several families of possible plate models (Fig. 2c). The final plate models (Fig. 2c) are fully-kinematic and make testable geological predictions for magmatic histories, palaeolatitudes and other geological events (e.g. collisions). These predictions can then be systematically compared against remnant geology (Fig. 2d), which are independent from the tomographic inputs (Fig. 2a).

The proposed 3D slab mapping workflow of Wu et al. (2016) assumed that the most robust feature of tomographic slabs is likely the slab center. The slab mapping workflow involved manual picking of a mid-slab ‘curve’ along hundreds (and sometimes thousands!) of variably oriented 2D cross-sections using software GOCAD (Figs. 3a, b). A 3-D triangulated mid-slab surface is then constructed from the mid-slab curves (Fig. 3c). Inspired by 3D seismic interpretation techniques from petroleum geoscience, the tomographic velocities can be extracted along the mid-slab surface for further tectonic analysis (Fig. 3d).

Figure 3: Slab unfolding workflow proposed by Wu et al. (2016) shown for the subducted Ryukyu slab along the northern Philippine Sea plate. The displayed tomography in a), d) and e) is from the MITP08 global P-wave model (Li et al., 2008).

For relatively undeformed upper mantle slabs, a pre-subduction slab size and shape can be estimated by unfolding the mid-slab surface to a spherical Earth model, minimizing distortions and changes to surface area (Fig. 3e). Interestingly, the slab unfolding algorithm can also be applied to shoe design, where there is a need to flatten shoe materials to build cut patterns (Bennis et al., 1991).  The three-dimensional slab mapping within GOCAD allows a self-consistent 3-D Earth model of the mapped slabs to be developed and maintained. This had advantages for East Asia (Wu et al., 2016), where many slabs have apparently subducted in close proximity to each other (Fig. 1).

Web resources for displaying tomography

Hades Underworld Explorer :

Seismic Tomography Globe :

SubMachine :



Bennis, C., Vezien, J.-M., Iglesias, G., 1991. Piecewise surface flattening for non-distorted texture mapping. Proceedings of the 18th annual conference on Computer graphics and interactive techniques 25, 237-246.

Hosseini, K. , Matthews, K. J., Sigloch, K. , Shephard, G. E., Domeier, M. and Tsekhmistrenko, M., 2018. SubMachine: Web-Based tools for exploring seismic tomography and other models of Earth's deep interior. Geochemistry, Geophysics, Geosystems, 19. 

Li, C., van der Hilst, R.D., Engdahl, E.R., Burdick, S., 2008. A new global model for P wave speed variations in Earth's mantle. Geochemistry, Geophysics, Geosystems 9, Q05018.

Shephard, G.E., Matthews, K.J., Hosseini, K., Domeier, M., 2017. On the consistency of seismically imaged lower mantle slabs. Scientific Reports 7, 10976.

Wu, J., Suppe, J., 2018. Proto-South China Sea Plate Tectonics Using Subducted Slab Constraints from Tomography. Journal of Earth Science 29, 1304-1318.

Wu, J., Suppe, J., Lu, R., Kanda, R., 2016. Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods. Journal of Geophysical Research: Solid Earth 121, 4670-4741

A belated happy new year!

A belated happy new year!

It was that time of the year again: holidays! Time to take a break from work, relax, and see all your friends and family again. The blog team is no different: we took a break from blogging for a little while as well, so you had to survive the holidays without us! Did you survive Christmas day without one of our blogposts? It must’ve been dreadful, I know, but that’s life! Luckily, we have some good news: we are back with some belated happy new year wishes and wintersport recommendations. We also tried to write limericks. Also also, we discuss chocolate and peppermint. Because we can. Cheers to a good blog year in 2019! 

Iris van Zelst

I once tried to ski down a slope
as friends thought there might be hope
I was covered in snow
from my head to my toe
If they invite me again it’s a ‘nope’

So, as many of you might have guessed, winter sports (or any sports, really) are not entirely my thing. Particularly skiing did not go down well for me. However, as a true Dutch girl, I do really enjoy ice skating and can recommend it thoroughly! However, this year no winter sports at all for me: I flew towards the sun in an effort to actually destress from work (feeble attempt as I brought my laptop, but still, kudos for trying, right?). I hope everyone had a very nice holiday and relaxing break. May all your (academic) wishes come true in 2019!

I also tried cross-country skiing once. That was infinitely better than alpine skiing. It was actually fun!

Grace Shephard

In hemispheric defiance of the “wintersport” edition, I am currently back Down Under where I have replaced the (seemingly eternal) television coverage of cross-country skiing with cricket, swapped a toboggan for me ‘togs’, and exchanged a pull-over for some ‘pluggers.’ I wish all of our blog readers a very happy and safe end to the year that was, and a fabulous start to the next!

What Aussies call swimming-related attire from

Anne Glerum

This year I spend winter in Berlin,
Where no snow has fallen and the ice is too thin.
So I drink myself heavy,
With hot chocolate and Pfeffi,
And wait for the fresh air of spring!

In the weeks before Christmas, Christmas markets dominate the streets of Berlin. Besides delicious food, they offer mulled wine and, as I discovered this year, hot chocolate with peppermintliqueur. A green version of the liqueur is made by Pfeffi, while a colorless Berlin-made peppermintliqueur is called Berliner Luft. It’s as clear and fresh as Berlin’s air according to the manufacturer. Although the freshness of Berlin’s air is debatable, the combination of chocolate and peppermint is delicious. I wish everybody a fresh start of the New Year with loads of hapiness!

Get conference ready!

Get conference ready!

It’s almost time for the AGU fall meeting 2018! Are you ready? Have you prepared your schedule and set up all your important business meetings? Here are some final tips to nail your presentation and/or poster!

Nailing your presentation
The art of the 15-minute talk: how to design the best 15-minute talk
Presentation skills – 1. Voice: how to get the most out of your presentation voice
Presentation skills – 2. Speech: how to stop staying ‘uh’

Making the best poster
Poster presentation tips: how to design the best poster layout
The rainbow colour map (repeatedly) considered harmful: how to make the best scientific figures