News

November workshops

2016-11-30 10.09.07

In November, Martina Ulvrova and Nicolas Coltice went to Utrecht to participate to the workshop organized by Jeannot Trampert to gather the people from the RheoMan project, iGeo project, ATUNE project and AUGURY. It was a 2 day workshop to share experiences on a common object: the Earth’s mantle.

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It was followed by the workshop in College de France in Paris on mantle flow, organized by Barbara Romanowicz and Patrick Cordier, where Nicolas Coltice gave a presentation. You can watch the video here.

 

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Bravo Docteur Bocher

Alexandre Fournier, Marie Bocher and Nicolas Coltice, after Marie's PhD defense.

Alexandre Fournier, Marie Bocher and Nicolas Coltice, after Marie’s PhD defense.

Marie Bocher defended her PhD on Friday November the 25th. The committee composed of  Luce Fleitout (Paris), Emmanuel Cosme (Grenoble), Tijana Janjic-Pfander (Munich), Georg Stadler (New York City), Stéphane Labrosse (Lyon) and Alexandre Fournier (Paris, co-advisor) and Nicolas Coltice (Lyon, co-advisor) congratulated her for her 3 year study on sequential data assimilation methods for mantle convection.

The PhD manuscript in english is available here: these_marie

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Un portrait de Claire Mallard dans Sciences pour tous

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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/

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Summer meetings

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.

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.

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Group photo of the SEDI meeting in Nantes.

 

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New paper: Subduction controls the distribution and fragmentation of Earth’s tectonic plates by Mallard et al. in Nature

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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

Screenshot 2016-08-22 12.52.07 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/

http://www.pourlascience.fr/ewb_pages/a/actu-le-puzzle-des-plaques-tectoniques-enfin-compris-37282.php

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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AUGURY @EGU 2016 in Vienna

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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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2nd AUGURY workshop @Valflaunès, France

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.

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.

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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.

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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.

The group on top of Pic Saint Loup.

 

Photographies courtesy of Charitra Jain and Dietmar Müller

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AUGURY @AGU Fall meeting 2015

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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 “A sequential data assimilation approach for the joint reconstruction of mantle convection and surface tectonics”

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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Art and geodynamics

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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/

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