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© NATALIA ALEJANDRA AUGURY Groundbreaking geology In an effort to accurately reconstruct the evolution of Earth’s mantle, Professor Nicolas Coltice is collaborating with researchers across the globe, using data assimilation and tectonic observations in a novel geological approach that will help inform a range of disciplines Our results will give better constraints on the paleogeography of the Earth, which is used in a variety of disciplines from palaeontology to mineral resource research. Reconstructing the evolution of the Earth’s mantle and surface tectonics together will allow sealevel reconstruction, which is fundamental for water resource research, for instance. Potentially, our models could provide a better description of tectonics than plate tectonics themselves. Why have previous mantle convection models been unable to describe how the internal structure of the mantle impacts surface tectonics and the dynamic feedback between tectonics and convection? Your work will create links between convection models and tectonic data. Can you summarise the context from which this project emerged and its intended impact? Plate tectonics allows geologists to reconstruct the position of the continents and evolution of the seafloor in Earth’s ‘recent’ past; however, it does not explain the forces that drive this motion. In contrast, mantle convection theory describes the forces behind the motions within the rocky mantle of the Earth, but fails to reproduce the surface tectonics. In collaboration with Professor Paul Tackley at the Swiss Federal Institute of Technology in Zurich and Tobias Rolf, a PhD student, we have for the first time produced mantle convection models that can make tectonic predictions – thus, linking tectonics and convection in a consistent manner is possible. As with the climate sciences, we now have a methodology to use both information from observations and models to make predictions. Instead of predicting what will happen in the future (forecasting), we can predict what happened in the past, during periods for which we are lacking geological data. Science progresses incrementally over time. The concepts and much of the understanding were already there, but the development of computational power and methods was fundamental. Most models were limited in some way – Professor Paul Tackley created a unique tool to partially resolve these problems. After years of appreciating our limitations, we may have given up on the idea of producing a model of mantle convection that could replace plate tectonic models. Although we remain far from achieving our goal, this new motivation is helping us develop convection models that can tackle the problem of connecting surface processes to the deep Earth in a dynamic manner. What methodologies will you use to unfold coinciding theories of tectonic and mantle evolution? We will use data assimilation to connect Earth tectonics and convection models. This method aims to find the best compromise between information using physics, a model, and data that describe the system from another point of view. Weather forecasting uses such methodology, as does finance, climate sciences, geomagnetism and other disciplines. How important is collaboration to this field of research? Can you discuss any partnerships with external researchers or laboratories in the course of your investigations? Collaboration is fundamental; we need diverse fields of expertise to combine models and data to make predictions about the Earth. Geological and geophysical observations require expertise in tectonics, petrology, marine geophysics and palaeomagnetism. Computer science is also very important: building optimised software for mantle convection and data assimilation cannot be made without strong proficiency in this field. We are working in collaboration with Professor Tackley, an expert in convection modelling, Professor Dietmar Müller, a specialist in global tectonics at the University of Sydney and Associate Professor Alexandre Fournier, a pioneer in data assimilation for geodynamics at the Paris Institute of Earth Physics. Can you outline the next steps to achieving the project’s overall objectives? I am working with several PhD students; initially to estimate the time over which models can be predictive – an issue on which we have made great progress. We are also developing a sequential data assimilation method. Currently, we are evaluating its ability to reconstruct the deep structure from surface data. This proof-of-concept step is important. Moreover, evaluating the models in more detail to see how they compare to the theory of plate tectonics is also significant to furthering our goals. It is essential to know where further progress is required, and where the models are efficient. Later this year we will begin to develop advanced data assimilation software, which should become our ultimate tool when completed in several years’ time. WWW.RESEARCHMEDIA.EU 115 AUGURY Model prediction of flow inside the Earth’s mantle. Colours at the surface show continents in blue and shearzones in red. Interior colours correspond to temperature: red represents high, and blue, low. Arrows at the surface characterise velocities. Modelling Earth’s history Knowledge of Earth’s palaeogeography is fundamental to a number of sciences, but accurately modelling the temporal dynamics of the planet has so far eluded researchers. The Europe-wide AUGURY project is developing innovative techniques to support this endeavour MORE THAN 50 years ago the theory of plate tectonics revolutionised understanding of the Earth’s surface and its evolution, building on the concept of continental drift to describe the largescale motion of the outermost shell of the Earth: the crust and upper mantle. Tectonic motion is caused by mantle convection, a process identified 30 years prior to plate tectonics, describing currents that carry heat from deep inside the Earth to the surface of the planet. representations of mantle dynamics. Coltice made a major breakthrough in a recent collaboration with Professor Paul Tackley at the Swiss Federal Institute of Technology (ETH) in Zurich, who has dedicated the past 20 years to developing mantle convection computational codes in spherical geometry, and Tobias Rolf, a PhD student at ETH. A geometry-based kinematic theory, plate tectonics does not take into account the Earth’s internal forces. Conversely, mantle convection theory is more comprehensive, and modelling offers the potential to provide imaging of past and present mantle thermochemical structure. However, in practice, convection models have mostly failed to generate surface tectonics that accurately reflect the Earth’s development, and the shift from plate tectonics to mantle dynamics is yet to be fully realised. Coltice plans to build on recent developments in order to reconstruct plate tectonics and convection history jointly MAJOR BREAKTHROUGH Professor Nicolas Coltice at the University of Lyon, France, has played a key role in contributing to new perspectives on how the Earth shaped its surface environment billions of years ago, through integrating geochemical and geophysical A. Temperature field in a 2D convection model with selfconsistent plate generation (red is hot and blue is cold). 116INTERNATIONAL INNOVATION For the first time, the researchers created mantle convection models that successfully generate surface tectonics comparable to the Earth, predicting tectonic and convection evolution using a single model. “There is still a long way to go, but our first approach allows us to compare results from first principles quantitatively with tectonic models produced by geologists,” Coltice reflects. While tectonic data are relatively restricted (it is not possible to build accurate reconstructions past B. Data assimilation (Kalman filter) of the temperature field using surface velocities and surface heat flow from model A. 200 million years), using models enables the team to compute billions of years of evolution. “We have used models to estimate how surface tectonics could behave over longer timescales than we can observe today,” adds Coltice. INNOVATIVE METHODOLOGIES In his current project, Reconstructing Earth’s Mantle Convection (AUGURY), on which Tackley is also collaborating, Coltice plans to build on these recent developments in order to reconstruct plate tectonics and convection history jointly. Using a multidisciplinary approach involving geodynamics, tectonics, mathematics and computer science, he is also collaborating with Professor Dietmar Müller – a specialist in global tectonics at the University of Sydney, Australia – as well as a number of PhD and postdoc students. The team aims to develop new methodologies using information from tectonic datasets and the physics of convection to produce a new generation of tectonic and convection reconstructions. As Coltice enthuses: “AUGURY will change not only our perspective on the deep Earth, but will also provide innovative tools and new information on fundamental Earth science issues”. The group plans to use data assimilation strategies in conjunction with existing tectonic data. This approach has never been used before in geodynamics, although it is widely exploited in disciplines such as meteorology, physical oceanography and climatology. Data assimilation combines information contained in numerical models describing the dynamics of a system with direct or indirect observations. Their methods will enable kinematic models to be built using mantle convection theory in place of plate tectonics. Furthermore, the team has recently produced a proof-of-concept tool using the Kalman filter – an advanced sequential data assimilation method. In parallel, Coltice also plans to develop a highperformance, sustainable, 4D variational data assimilation (4D-Var) code that embeds the code developed by Tackley – StagYY – and its adjoint INTELLIGENCE AUGURY RECONSTRUCTING EARTH’S MANTLE CONVECTION OBJECTIVES To reconstruct the history of the movements of the solid Earth, from the surface to the deep mantle. PARTNERS Université Claude Bernard Lyon 1, France Ecole Normale Supérieure de Lyon, France Plate tectonic reconstruction of the Earth 100 million years ago, provided by Professor Dietmar Müller’s Earthbyte group. code. “This has more potential than the Kalman filter approach: the formulation is more complete and will allow hindcasting,” he explains. This part of the project will require expertise in advanced mathematical physics, as the adjoint code will need Diagrams showing a model of plate tectonics with three plates. Transform faults are in red and the rotation axis of the relative motion between the blue and yellow plates is demonstrated. Figure taken from teaching material at geosciences3d.univ-lyon1.fr. to be specially developed. The 4D-Var code will be evaluated against synthetic and real data, and its performance will be compared to the Kalman filter methodology for cases with similar settings. Centre National de Recherche Scientifique, France Institut Universitaire de France, France Eidgenössische Technische Hochschule Zürich, Switzerland UNPARALLELED INSIGHT University of Sydney, Australia Dissemination of results is a major component of AUGURY’s work. This will include publicising data, developing teaching materials and creating a digital hub accessible online for scientists, teachers and the public. The hub will be designed to keep track of the tools being developed as well as the results generated, and will make the AUGURY models publicly available in addition to statistical descriptions of relevant convection solutions obtained throughout the course of the project. Those interested in the project’s findings will be able to contribute to or use what the team creates, and the shared data can be used to interpret geophysical and geological data and models. “Sharing our results with other research groups is very important in order to respect what science is: a humanist discipline,” adds Coltice. “I believe that collaborating to solve problems can have a positive impact in our discipline and beyond.” FUNDING AUGURY represents an innovative, transformative step in the study of the solid Earth, and its findings will impact a variety of geological disciplines. By reconstructing the evolution of the 3D mantle structure, Coltice and his team will be able to work with seismologists and mineral physicists who need information about the causes of seismic anomalies in the deep Earth. “We will be able to tell them if temperature alone is causing these anomalies, for instance. This question is long-standing and we will bring new perspectives to it,” Coltice reiterates. In addition, elucidating the changing 3D structure of the planet’s mantle will help scientists understand the evolution of Earth’s geomagnetic field. Finally, because the rotation of the planet is influenced by mass redistribution within the mantle, Coltice’s work could also contribute to elucidating further constraints on this issue. “If all goes to plan, we will finally reconstruct the deep Earth from geological data, connecting the surface to the depths and realise tectonic reconstruction in a more global framework than plate tectonics,” he concludes. “With geological data, we should be able to image the deep Earth too, not just for the present day, but also for ancient times. It is a new window to the recent history of the solid Earth.” www.augury.eu The European Research Council within the framework of the SP2-Ideas Program ERC2013-CoG CONTACT Professor Nicolas Coltice Project Coordinator Université Claude Bernard Lyon 1 Laboratory of Geology of Lyon Batiment Geode 43 Boulevard du 11 Novembre 1918 69622 Villeurbanne Cedex France T +33 4 72 43 27 41 E [email protected] NICOLAS COLTICE is a geodynamicist whose research has focused on the solid Earth. He is using modelling to bridge the gap between observations and theories to reconstruct the evolution of Earth from its beginning to its recent geologic past. He has also conducted educational projects at national and European level. WWW.RESEARCHMEDIA.EU 117