The early stages of subduction

Dr Douwe J J van Hinsbergen reflects on his efforts to shed new light on the mechanisms of plate

SINK tectonics, attempting to determine the processes that lead to the formation of new subduction zones

From what context did your investigation make plate reconstructions of these mountain into Subduction Initiation reconstructed from belts. Normal plate reconstructions assume Neotethyan Kinematics (SINK) emerge? that plates are rigid, they cannot deform and their motion is accommodated along narrow, During my PhD and first two postdoctoral discrete fault zones. Although this approach positions, I studied the formation and evolution is very useful for reconstructing plate motion of mountain belts in the wider Neotethyan on a global scale, it is not directly applicable realm. The Neotethys was a major oceanic to regions where plates converge and where basin system that existed between Gondwana one plate subducts below another – in in the south (a major continental realm that these places, plate boundary zones show contained Africa, Arabia, India and Australia) distributed, spectacular deformation. Using and Laurasia in the north (Eurasia, Greenland structural geological and palaeomagnetic and North America). Its closure eventually data, I have built detailed retro-deformation formed the Alpine-Himalayan mountain belt. models of these mountain belts. From these models, I can derive when and where During my third postdoctoral position at the subduction zones started to form, and along University of Oslo in Norway, I started to what structures.

106 INTERNATIONAL INNOVATION SINK

Can you provide an overview of your approach to study the driving forces behind back to the time of their onset, we aim to current project and outline the main aims plate tectonics? define what processes cause the formation of your research? of subduction zones. Is the collision between I have begun to collaborate with geophysicists, two continents sufficient to perturb the SINK mainly focuses on subduction zones that some of whom develop models for the structure forces driving the plate tectonic cycle and existed within the Neotethys Ocean, since of the Earth’s mantle where former surface develop a new subduction zone along a these leave a very distinct rock record known plates can be found that have subducted in the former mid-ocean ridge – or could this only as ‘ophiolites’ – pieces of oceanic crust that geological past; other partners create numerical happen under certain circumstances? Do were thrust over continental margins and models that try to explain elements of plate these apply to the reconstructed history? We which are now exposed on land. motion and subduction based on basic physical will combine the reconstructions with tailor- laws and principles. While geologists can only made numerical models to test whether This particular project aims to create a speculate about the causes and consequences geologists’ speculations are physically breakthrough in our understanding of plate of subduction, geophysicists can show what possible and if the models actually match tectonics by identifying the processes that is theoretically possible. Much of the time, the observations. have led, and may lead, to the formation geophysicists do not know the details of what of new subduction zones. As common as actually happened, so the application of their What are your expectations for the future subduction may be, and as long as we have results alone is not always sufficient. of your research? known of its occurrence, this question has never really been asked and has not been In your research, you reconstruct the By moving beyond studying generic aspects analysed in detail. In more general terms, I geometry and orientation of a subduction of Earth’s behaviour, and isolating what aim to integrate the field of geology (that is, zone at the moment subduction started. exactly happened in terms of the geology and observational analysis of fossils, structures, What questions are you hoping to physics of subduction zone formation in the rocks and minerals) with physics through answer and how do you combine these Neotethys, I hope we can better understand numerical modelling. reconstructions with numerical models? the physics of particular case studies. In the future, I would also like to include the more Could you explain the importance of using Given my interest in subduction zones and detailed geochemistry of mantle-derived an integrated geological and numerical the ability to reconstruct their configuration rocks (volcanoes) in the analysis.

Solving the secrets of subduction

Using unprecedented multidisciplinary research methods, the SINK project based at Utrecht University is breaking new ground in its studies of the driving forces behind the initiation of subduction zones

OF EXISTING GEOLOGICAL theories, plate There is currently no widely accepted entitled Subduction Initiation in Neotethyan tectonics is one of the most revolutionary and physical explanation for what drives plate Kinematics (SINK), van Hinsbergen employs influential. Supported by a weighty and diverse tectonics. While there is broad agreement a highly multidisciplinary approach that is body of evidence, the theory mathematically that the mechanism involves thermal essential to the work’s success. describes the complex evolution of the Earth’s convections in the Earth’s mantle that result lithosphere in terms of constantly shifting in interior cooling, it is only recently that Once stretching between the two plates and their interactions. Understanding technological advances have made it possible supercontinents – Gondwana in the south and plate tectonics is not only important for to reconstruct and explore the dynamic Laurasia in the north – the Neotethys Ocean explaining mountain formation and the history of the mantle itself. on which van Hinsbergen’s study focuses creation of a wide range of georesources, but contains many well-dated and well-exposed it is also vital for predicting natural hazards ophiolites (fragments of oceanic crust) that NEOTETHYAN KINEMATICS such as earthquakes. hold the best-preserved geological record of Dr Douwe J J van Hinsbergen – a structural past subduction initiation events. Subduction of oceanic lithosphere into geologist, palaeomagnetist and field geologist the Earth’s mantle – the process by which – has dedicated his career to the tectonic ‘Kinematics’ refers to the mathematical one tectonic plate is pushed downwards reconstruction of mountain belts. Based at calculation of past movements of the beneath another as the two converge – is a the Department of Earth Sciences at Utrecht Earth’s crust: “We are building a model that key element of plate tectonics. Geophysical University, The Netherlands, he is currently mathematically describes the motions of models demonstrate that forcing is required leading a research project that aims to further all crustal blocks that were involved in the to initiate subduction at weakness zones, understand plate tectonics by identifying the closure of the Neotethys Ocean,” explains van but mechanisms producing this forcing mechanisms that force subduction initiation. Hinsbergen. “The theory of plate tectonics is remain unexplored. A year and a half into the five-year project, kinematic in that it describes the motion of

WWW.RESEARCHMEDIA.EU 107 INTELLIGENCE SINK SUBDUCTION INITIATION RECONSTRUCTED FROM NEOTETHYAN KINEMATICS OBJECTIVES • To unravel the processes causing the formation of subduction zones – a key link in the plate tectonic cycle – through geological one plate relative to another. Kinematics is the plate can be offscraped and accreted to the reconstruction and geophysical modelling expression of dynamics, the set of forces that overriding plate. explain why these movements occurred. That is • To develop a predictive model for our ambition: a dynamic explanation.” The researchers led by Van Hinsbergen build exploration of subduction-related models of converging plates using modern- georesource formation day ocean floors: “Our reconstructions A NOVEL APPROACH KEY COLLABORATORS begin in the present day and then recreate Subdivided into several smaller projects, SINK historical Neotethys plate movements step Marco Maffione; Ayten Koç (Postdoctoral is integrating geology and geophysics in a way by step, to the best of our knowledge placing researchers); Derya Gürer; Kalijn Peters; that will help to forge a deeper understanding of all the rocks that are now at the surface back Peter McPhee (PhD students) • Wim subduction initiation: “I have a team of talented into their position when they formed,” he Spakman; Cedric Thieulot; Liviu Matenco; people under my supervision, each with specific explains. Using these reconstructions it is Martyn Drury; Herman van Roermund, aptitudes and skills,” van Hinsbergen enthuses. possible to restore the geological units of a Utrecht University, The Netherlands • Fraukje “Through the combination of our expertise we mountain belt to their configuration before Brouwer, VU University, The Netherlands • hope to gain insights that we wouldn’t be able subduction started to deform them. From Nuretdin Kaymakci, Middle East Technical to develop individually.” this, the researchers can model the geometry University, Turkey • Ercan Aldanmaz, Kocaeli and orientation of a subduction zone at the University, Turkey • Paul Kapp; Peter Lippert, Subduction initiation events, absolute and moment the process began. University of Arizona, USA • Fernando Corfu; relative plate motions, continental subduction Trond Torsvik, Oslo University, Norway • and mantle plumes can be reconstructed in Using advanced palaeomagnetic analyses, the Morgan Ganerød, Norwegian Geological the Alpine-Himalayan mountain belt, a natural team is able to map the spreading of the mid- Survey • Stefan Schmid, The Swiss Federal laboratory that formed during the closure of the ocean ridge at which ophiolites were formed. Institute of Technology, Zurich Neotethys Ocean. Its young age makes it an Determining the orientation of the Earth’s FUNDING ideal study site, as the important features the magnetic field – which is frozen into these team needs for its research remain present in oceanic rocks – allows the researchers to predict European Research Council (ERC) – Starting the rock record. An added advantage is that the the tilting and rotation an ophiolite may have grant no. 306810 area is well studied, meaning there is already undergone since its formation at the ridge. Using Dutch Organisation for Scientific Research an existing wealth of information. A numerical this information, they are able to derive the (NWO) – VIDI grant no. 864.11.004 laboratory has also been designed to conduct positioning of the lithosphere at the moment modelling experiments that test whether the of subduction initiation. Conclusions can then CONTACT geological incidents are causally related. be drawn about the relationship between Dr Douwe J J van Hinsbergen the spreading ridge and the alignment of the Principal Investigator The combination of geological and subduction zone. This leadsvan Hinsbergen to geophysical techniques makes the project believe that their research will also reveal other Department of Earth Sciences unique. Integration of geophysical modelling major processes that occurred elsewhere on the Utrecht University allows the team to test each step of their planet, for example, major volcanic episodes or Budapestlaan 4 geology-based hypotheses: “If we can isolate continent-continent collisions. 3584 CD those conditions, we can go back to our Utrecht reconstruction, and from that to the field to FUTURE IMPLICATIONS The Netherlands test whether our inferences are possible, or whether we need to go back to the drawing By iteratively integrating data obtained from the T +31 627 283 719 board to test other key predictions made by natural and numerical laboratories to further E [email protected] the physical models,” van Hinsbergen reveals. understand the processes driving subduction, it is hoped that a breakthrough will be made in DR DOUWE J J VAN HINSBERGEN is SINK is also involved in several collaborations; developing a dynamic and quantitative model Associate Professor at the University of the researchers work with colleagues at the to explain plate tectonics. Utrecht. He constructs plate tectonic Middle East Technical University and Kocaeli restorations of mountain belts, including University in Turkey on the Anatolian projects, Gaining a comprehensive and detailed ophiolites within those, at subduction and with colleagues at the University of Arizona understanding of the Earth’s physical processes zones and uses these to constrain dynamic in Tucson, USA, on the Himalayan projects. They also has significant repercussions for the numerical models of subduction initiation also have partners at the University of Oslo, lives and security of future generations. and evolution. Norway, and the Norwegian Geological Survey Ultimately, SINK will pave the way for a more in Trondheim working on the dating of rocks. thorough assessment of seismic hazards, and for the identification of locations where ore deposits and hydrocarbons may be found: “An RETRACING SUBDUCTION INITIATION understanding of the physics of the Earth allows Subduction results in a very distinct set of us to obtain predictive hypotheses of what we geological features, generating volcanic may expect to find where, how an area may belts and mountain chains that have specific behave in the future or must have behaved in chemistries, structures and rock types. During the past,” elucidates van Hinsbergen. “This is the process, rocks from the subducting the Holy Grail of natural science.” 108 INTERNATIONAL INNOVATION