Un portrait de Claire Mallard, doctorante au sein du projet AUGURY, a été réalisé pour Sciences pour tous. C’est par ici : https://sciencespourtous.univ-lyon1.fr/claire-mallard-revue-nature/
Read more →This summer was the occasion of sharing progress made on the AUGURY project. In July, Martina Ulvrova and Nicolas Coltice attended the Plate tectonics workshop organized by Paul Tackley and his group, together with Robert Stern. It was in Locarno, Switzerland, a beautiful place in the Alps. Many discussions focused on when plate tectonics started, and a next meeting is planned with expectations of significant advances in the near future. Martina Ulvrova presented her work on the life of subduction zones, Charitra Jain on continental lithosphere formation in convection models, Antoine Rozel on grain size evolution.
Group photo in Ascona for the Plate tectonics workshop.
Following this workshop, the SEDI meeting in Nantes, France, was the gathering of deep Earth scientists working on the deep interior of the Earth and planets. Maelis Arnould presented her work on dynamic topography, and Nicolas Coltice attended the workshop. Tobias Rolf presented his work on tectonics and mantle convection. The meeting gave the opportunity for long group discussions on deep dynamics, and sharing between different communities.
Group photo of the SEDI meeting in Nantes.
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The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates1 of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years suggests that this layout is probably a long-term feature of Earth, but the forces governing it are unknown. Previous studies3, 5, 6, primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection.
Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size–frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates7, 8 reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected.
Download the preprint here: http://geologie.ens-lyon.fr/augur/wp-content/uploads/2016/08/Mallard2016_augury.pdf
http://www.nature.com/nature/journal/v535/n7610/full/nature17992.html
News about this work:
https://earth-pages.co.uk/2016/07/11/here-is-the-plate-tectonic-forecast/
https://lejournal.cnrs.fr/articles/le-puzzle-des-plaques-tectoniques-enfin-resolu
https://www.ethz.ch/en/news-and-events/eth-news/news/2016/07/a-most-irregular-puzzle.html
http://www.earthbyte.org/solving-earths-giant-jigsaw-puzzle-of-tectonic-plates/
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From left to right: M. Arnould, M. Bocher, D. Bower, S. Brändli, P. Tackley, M. Gérault, N. Coltice, N. Flament and C. Jain.
EGU 2016 took place in Vienna between the 17th and the 23rd of April. We presented our work in progress through 4 posters from the team in Lyon. Nicolas Flament (Sydney) presented his work, as well as the team of Zurich. The meeting was a chance for Maelis Arnould, who started her PhD in September, to sit with her two advisors from across oceans (N. Flament and N. Coltice).
The group of Lyon presented a poster and a presentation at the session organised by Claudia Alves de Jesus Rydin (ERC): « Promoting and supporting equality of opportunities in geosciences ». As a feminine group, we were happy to share our experience on how we try to promote women in sciences, focusing on local actions and emphasizing democracy through a flat organisation. It was the occasion to speak with people on this subject that matters a lot for us.
N. Coltice gave a talk about getting funded through ERC, pointing that it is a difficult but important task to find ways to take into account the decline of funding for the operation of everyday collectivity.
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From left to right: Dietmar Müller, Martina Ulvrova, Antoine Rozel, Andrew Meredith, Charitra Jain, Tobias Rolf, Mélanie Gérault, Nicolas Coltice, Claire Mallard, Paul Tackley, Dan Bower, Marie Bocher, Stefan Brändli, Maelis Arnould, Simon Williams.
The second AUGURY workshop took place in Valflaunès, France between the 14th and the 18th of February. The groups from Zurich, Sydney and Lyon, and Tobias Rolf from Oslo joined in the beautiful Château de Valflaunès for sessions of work. The goal was to assess the progress made by the different groups, and to share experience, technology and knowledge. It was also the possibility for us to work as smaller groups on issues and new collaborations.It was very fruitful and we made some steps in the modeling and on how to connect it with geologic data.
Tutorials on StagYY, GPlates and the data assimilation tool Marie Bocher developed recently were interesting times to enter the skin of people of different backgrounds. Martina Ulvrova presented the Python library she contribute to develop with Stéphane Labrosse and his team to analyze Stag outputs. Everyone pushed for more technology sharing. The presence of Dietmar Müller, Simon Williams and Andrew Meredith from EarthByte was very important to start bridging more closely the convection models and the plate tectonic reconstructions. Over the workshop, Paul Tackley identified some significant improvements that will be made to make a step forward in the modeling.
The workshop took place in a wonderful atmosphere, and the sun was there to allow the hike of the Pic Saint Loup on the free afternoon. Everyone is looking forward the next workshop, but a meeting of the groups is already schedule for next EGU meeting in Vienna.
The group on top of Pic Saint Loup.
Photographies courtesy of Charitra Jain and Dietmar Müller
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Marie Bocher, Claire Mallard, Martina Ulvrova and Nicolas Coltice attended AGU 2015 fall meeting. A group from E.T.H. Zurich with Charitra Jain, Antoine Rozel and Paul Tackley, as well as a team from Sydney with Simon Williams presented works as well.
It was the occasion to present the latest results from the project: Marie Bocher presented a poster on Ensemble filter method that will enable us to perform data assimilation in 3D spherical geometry in the course of 2016; Claire Mallard showed her analysis of convection models to understand why plates have specific size distribution; Martina Ulvrova presented results on convection with a free surface and continents, and Nicolas Coltice presented a work on small scale convection and a work on predicting tectonics with convection models.
The conference was the occasion to share knowledge and experience with colleagues around the globe and show how our team progressed in the past two years.
Movie of small scale convection beneath the lithosphere in a convection model. The view is from below. The red isotherm represents plume interacting with the boundary layer.
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New paper published in Geophysical Journal International, as a collaboration between the team in Lyon, Alexandre Fournier from Paris, our mentor in Data Assimilation, and Paul Tackley from Zurich. The manuscript, a part of the PhD work of Marie Bocher, presents a proof of concept of using tectonic information to reconstruct the convective evolution in the mantle. Check it here: Bocher_et_al_Augury
Abstract
With the progress of mantle convection modelling over the last decade, it now becomes possible to solve for the dynamics of the interior flow and the surface tectonics to first order. We show here that tectonic data (like surface kinematics and seafloor age distribution) and mantle convection models with plate-like behaviour can in principle be combined to reconstruct mantle convection. We present a sequential data assimilation method, based on suboptimal schemes derived from the Kalman filter, where surface velocities and seafloor age maps are not used as boundary conditions for the flow, but as data to assimilate. Two stages (a forecast followed by an analysis) are repeated sequentially to take into account data observed at different times. Whenever observations are available, an analysis infers the most probable state of the mantle at this time, considering a prior guess (supplied by the forecast) and the new observations at hand, using the classical best linear unbiased estimate. Between two observation times, the evolution of the mantle is governed by the forward model of mantle convection. This method is applied to synthetic 2-D spherical annulus mantle cases to evaluate its efficiency. We compare the reference evolutions to the estimations obtained by data assimilation. Two parameters control the behaviour of the scheme: the time between two analyses, and the amplitude of noise in the synthetic observations. Our technique proves to be efficient in retrieving temperature field evolutions provided the time between two analyses is 10 Myr. If the amplitude of the a priori error on the observations is large (30 per cent), our method provides a better estimate of surface tectonics than the observations, taking advantage of the information within the physics of convection.
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©Samuel Maillot
Lea Bello and Samuel Maillot worked on a picture in the These’s art festival. Check this out here (in french): https://sciencespourtous.univ-lyon1.fr/theses-art-lea-bello-manteau-terrestre/
Read more →New paper published in Earth and Planetary Science Letters, as a collaboration between Lyon, Zurich and Sydney. The manuscript, a part of the PhD work of Léa Bello, shows how rheology influences the numerical solutions obtained when driving a convection model with surface plates. Check it here: Belloetal2015.
Abstract
Reconstructing the 3D structure of the Earth’s mantle has been a challenge for geodynamicists for about 40 yr. Although numerical models and computational capabilities have substantially progressed, parameterizations used for modeling convection forced by plate motions are far from being Earth- like. Among the set of parameters, rheology is fundamental because it defines in a non-linear way the dynamics of slabs and plumes, and the organization of lithosphere deformation. In this study, we evaluate the role of the temperature dependence of viscosity (variations up to 6 orders of magnitude) and the importance of pseudo-plasticity on reconstructing slab evolution in 3D spherical models of convection driven by plate history models. Pseudo-plasticity, which produces plate-like behavior in convection models, allows a consistent coupling between imposed plate motions and global convection, which is not possible with temperature-dependent viscosity alone. Using test case models, we show that increasing temperature dependence of viscosity enhances vertical and lateral coherence of slabs, but leads to unrealistic slab morphologies for large viscosity contrasts. Introducing pseudo-plasticity partially solves this issue, producing thin laterally and vertically more continuous slabs, and flat subduction where trench retreat is fast. We evaluate the differences between convection reconstructions employing different viscosity laws to be very large, and similar to the differences between two models with the same rheology but using two different plate histories or initial conditions.
Mélanie and Marie on the deck
From the 31st of August to the 5th September, Mélanie Gérault and Marie Bocher attended the XIV International Workshop on Modelling of Mantle and Lithosphere Dynamics in the French island Oléron (https://sites.google.com/site/geodynamicsxiv/). It was a great opportunity for both of them to discuss, discover, and exchange ideas with the geodynamic modelling community. Mélanie presented a poster on flat-slab subduction, topography, and mantle dynamics in southwestern Mexico, research on which she worked toward the end of her Ph.D. with Laurent Husson (U. of Grenoble), Meghan Miller (USC), and Gene Humphreys (U. of Oregon). Marie presented a poster on applying data assimilation to mantle circulation and surface tectonics, which constitutes the first chapter of her Ph.D. thesis. It also gave them the opportunity to meet with a few collaborators of the Augury project: Paul Tackley, Tobias Rolf, Nicolas Flament, Charitra Jain and Antoine Rozel. One of the highlights of the week was a boat tour to Fort Boyard, in front of which Marie and Mélanie are pictured below! Many thanks to Laetitia Le Pourhiet and cowokers (UPMC) for organizing such a stimulating and enjoyable meeting.
Following the meeting, we had the opportunity to host Nicolas Flament from the University of Sydney, who is co-advisor of the starting PhD thesis of Maelis Arnould, and Shi Joyce Sim from the University of San Diego, working on a project about sea-level in the deep past. It was a busy week with a lot of fruitful discussions.
On the 23rd of September, Nicolas Coltice attended the Research Data Alliance plenary meeting to discuss sharing 3D data in Earth Sciences, in a session organized by BRGM.
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