New publication in Frontiers in Earth Science

Deformation of Polycrystalline MgO Up to 8.3 GPa and 1270 K: Microstructures, Dominant Slip-Systems, and Transition to Grain Boundary SlidingWe have a new publication! On May 9th, 2022, former TIMEleSS PhD student Estelle Ledoux published a new paper in Frontiers in Earth Science: Deformation of Polycrystalline MgO Up to 8.3 GPa and 1270 K: Microstructures, Dominant Slip-Systems, and Transition to Grain Boundary Sliding.

The work is a result of a collaboration between the Université de Lille and the University of Utah. We focus on polycrystalline periclase, the pure Mg end-member of the second-most abundant mineral in the Earth lower mantle, ferro-periclase, for which mechanical properties are important to understand flow and the dynamics of the Earth mantle.

we deform polycrystalline periclase at conditions ranging from 1.6 to 8.3 GPa and 875–1,270 K. We analyse the flow laws and microstructures of the recovered samples using electron microscopy and compare our observations with predictions from the literature. We identify a first mechanism for samples deformed at 1,270 K, attributed to a regime controlled by grain boundary sliding accommodated by diffusion, and characterized by a small grain size, an absence of texture, and no intracrystalline deformation. At 1,070 K and below, the deformation regime is controlled by dislocations. The samples show a more homogeneous grain size distribution, significant texture, and intracrystalline strains. In this regime, deformation is controlled by the ⟨110⟩{110} slip system and a combined ⟨110⟩{110} and ⟨110⟩{100} slip, depending on pressure and temperature.

Based on these results, we propose an updated deformation map for polycrystalline MgO at mantle conditions and discuss the implications for ferropericlase and seismic observations in the Earth’s lower mantle.

More details can be found in the open-access full reference of the study: E. E. Ledoux, F. Lin, L. Miyagi, A. Addad,  A. Fadel, D. Jacob, F. Béclin, and S. Merkel. Deformation of Polycrystalline MgO Up to 8.3 GPa and 1270 K: Microstructures, Dominant Slip-Systems, and Transition to Grain Boundary Sliding. Front. Earth Sci. 10, 849777 (2022) [doi: 10.3389/feart.2022.849777]

New publication in Physical Review Materials

Deformation and slip systems of CaCl2-type MnO2 under high pressureWe have a new paper release ! On May 3rd, 2022, TIMEleSS student Matthias Krug, PI Carmen Sanchez-Valle, and PI Sébastien Merkel published a paper in Physical Review Materials, along with Binbin Yue and Fang Hong from the Center for High Pressure Science & Technology in Beijing, China.

The paper focuses on deformation in MnO2 and particularly its high pressure phase, in the CaCl2 structure. Why do we care about MnO2 ? MnO2 is not a deep Earth material, but it can be used as an analogue for SiO2 stishovite, which crystalizes in a rutile structure at low pressure and transform to a denser CaCl2 structure under high pressure. In SiO2, the stishovite to post-stishovite transformations occurs at ~ 50 GPa and is not always easily reached in deformation experiments. In MnO2, this same structural transition occurs at much lower pressure, around 4 GPa.

Our results show that, after phase transition to a CaCl2 structure above 3.5 GPa, the dominant (010)[100] and secondary {110}[001] and {011}[0-11] slip systems induce a 121 texture in compression. Further compression increases the activity of the {011}011 slip system, with an enhanced 001 texture at 50GPa. Finally, MnO2 transforms back to a rutile structure upon pressure release, with a significant orientation memory, highlighting the martensitic nature of the CaCl2 to rutile structural transformation. Overall, these results help us understanding plasticity and microstructures of CaCl2-structured dioxides, with implications in materials and Earth and planetary science.

The full reference for the study: B Yue, M. Krug, C. Sanchez-Valle, S. Merkel, and F. Hong, Deformation and slip systems of CaCl2-type MnO2 under high pressure, Phys. Rev. Mater., 6, 053603 (2022) [doi: 10.1103/PhysRevMaterials.6.053603]

New publication in Geophysical Journal International

Mapping the edge of subducted slabs in the lower mantle beneath southern AsiaOn March 23rd, 2022, TIMEleSS student Federica Rochira, published a new paper in Geophysical Journal international: Mapping the edge of subducted slabs in the lower mantle beneath southern Asia.

In this work, Federica Rochira, Lina Schumacher, and Christine Thomas from the Westfälische Wilhelms-Universität, Münster, investigate the presence of seismic structures in the Earth’s mantle by searching for seismic signals, and in particular signals from the edges of subducted slabs. They rely on an original approach that uses was that travel off the great circle path direction and are reflected or scattered off structures in the lower mantle and focus on areas of current and past subduction beneath Eurasia by using events from Indonesia and Japan recorded at the broad-band stations in Germany, Morocco and Namibia. Applying seismic array techniques, they measure the direction and traveltime of the out-of-plane arrivals and backtrace them to their location of reflection/scattering.

The results of the work indicate that most of the backtraced reflectors are located beneath southern Asia and are found shallower than 1500 km depth. They correlate well with the edges of prominent high velocity anomalies in tomographic inversions beneath southern Asia, which have been interpreted as remnants of fossil slabs of the subduction of the Tethys Oceans. They also observe few reflectors deeper than 1600 km that are located away from subducting regions and their positions coincide with the eastern edge of the African low velocity anomaly.

These observations suggest that the presence of reflectors in the mid-lower mantle is not exclusively related to current or past subducting regions, but widespread throughout the mantle.

The full details are in the following publication: F. Rochira, L. Schumacher, C. Thomas, Mapping the edge of subducted slabs in the lower mantle beneath southern Asia, Geophysical Journal International, 230, 1239–1252 (2022) [doi: 10.1093/gji/ggac110]

TIMEleSS members at the AGU Fall Meeting in New Orleans

2021 AGU Fall Meeting, New OrleansTIMEleSS members attended the Fall Meeting of the American Geophysical Union in December 2021. S. Merkel and J. Gay travelled to New Orleans, in the United States, and attended the meeting in while E. Ledoux presented her work remotely.

J. Gay presented his work on the Experimental Investigation of Microstructures at the 660 km discontinuity as a poster while E. Ledoux had the opportunity to give two talks on Dislocation Slip In Wadsleyite And Its Implications For The Seismic Anisotropy In The Mantle Transition Zone and on Deformation Mechanisms In Fine-grained MgO Periclase At Pressures Of 1.6-8.3 GPa And Temperatures Of 875-1270 K. Nice overview of upcoming publications.

It was nice to meet people in person again and we hope that, next time, the whole team will manage to make it in person!

TIMEleSS members at the Collège de France

Collège de France - Global Scale Seismic Imaging and Dynamics of the Earth’s MantleTIMEleSS members C. Thomas, S. Merkel, J. Gay, E. Ledoux, J.K. Magali are at the Collège de France for a workshop on Global Scale Seismic Imaging and Dynamics of the Earth’s Mantle organized by Barbara Romanowicz, chair for Deep Earth Physics at the Collège de France.

TIMEleSS PI S. Merkel and C. Thomas are presenting keynote lectures on Phase transitions in the mantle: effect on microstructures and seismic observables and Investigating deformation in the mantle through seismological observations. Students J. Gay and E. Ledoux also presented posters with their latest results on the transition zone and lower mantle.

First in-person meeting in many months!

John Keith Magali joins the TIMEleSS project!

John Keith MagaliJohn Keith Magali is a post-doc for the TIMEleSS project at the Université de Lille since September 2021.

After undergraduate studies in the Philippines he joined the International Center for Theoretical Physics in Trieste for a post-graduate diploma, followed by a PhD at the Université de Lyon. He is interested in inversion techniques of seismic data and how seismic data can be used as a constrain for geodynamics.

In TIMEleSS, John Keith will be in charge of studying the effect of mineral microstructures on elastic wave propagation and upscaling mineral physics knowledge to the scale of seismic observations.

Welcome!

Publication in the European Journal of Mineralogy!

Publication in the European Journal of Mineralogy: Deformation of NaCoF3 perovskite and post-perovskite up to 30 GPa and 1013 K: implications for plastic deformation and transformation mechanismA new publication from a TIMEleSS student in the European Journal of Mineralogy : Deformation of NaCoF3 perovskite and post-perovskite up to 30 GPa and 1013 K: implications for plastic deformation and transformation mechanism.

Jeff Gay uses a resistively heated diamond anvil to study the plastic deformation and phase transformation mechanisms in NaCoF3. Under ambient pressure, NaCoF3. crystallizes in the perovskite structure, and later transforms to the post-perovskite. It is hence an excellent analogue to understand the physical properties of bridgmanite, the most abundant mineral on Earth, and dominant component of the Earth’s lower mantle between 660 and 2900 km depth.

These results from a collaboration between the Université de Lille, the University of Utah, University College London, and the PETRA III / DESY synchrotron source were published on 30 Sep 2021 in the European Journal of Mineralogy.

Full reference: J. P. Gay, L. Miyagi, S. Couper, C. Langrand, D. P. Dobson, H.-P. Liermann, S. Merkel, Deformation of NaCoF3 perovskite and post-perovskite up to 30 GPa and 1013 K: implications for plastic deformation and transformation mechanism, European Journal of Mineralogy, 33, 591–603 (2021), abstract [doi: 10.5194/ejm-33-591-2021].

Ernst-von-Rebeur-Paschwitz-Preis for Tine Thomas

Ernst-von-Rebeur-Paschwitz-Preis for Tine ThomasTIMEleSS PI Tine Thomas received the Ernst-von-Rebeur-Paschwitz-Preis from the Deutschen Geophysikalischen Gesellschaft in 2020 for her sustained excellence in science. The medal was awarded in 2020 with a virtual celebration ceremony in 2021.

Ernst von Rebeur-Paschwitz was an astronomer, geodesist and geophysicist, famous for his work on horizontal pendulums to record long-distance earthquakes. He also proposed to create an international network of seismological stations and this idea led to the founding of the International Seismological Association.

Since 2004, the DGG honors outstanding scientific achievements in the field of geophysics with the Ernst von Rebeur Paschwitz Prize. The target group are researchers from Germany or abroad who are in the middle or advanced stages of their careers, with an award every 2 to 4 years.

 

TIMEleSS at the AGU Fall Meeting

AGU Fall Meeting 2020

The Fall Meeting of the American Geophysical Union is on online and everywhere in 2020! The AGU Fall Meeting typically attract over 25 000 registrants from all over the world, in a conference center somewhere in San Francisco, New Orleans, or somewhere else in the United States. This year, the Fall Meeting is fully online and TIMEleSS members are happily joining in for presenting their latest results!

Presentations from the TIMEleSS project include

Enjoy your AGU fall meeting!

We are hiring!

Post-doctoral position at the Université de Lille, starting in 2021The TIMEleSS project is looking for a post-doctoral fellow. The position is available in 2021 and extendable until the end of 2022. The position is attached to the Earth and Planetary Materials group the Unité Matériaux et Transformations, at the Université de Lille, France, with strong collaborations with the Institute for Geophysics at the University of Münster.

The candidate should have a strong background in deep Earth seismology and/or wave propagation in complex media and/or mineral physics and will be in charge of connecting mineral physics knowledge of phase transformations and microstructures in the Earth’s mantle to potential observations of seismic reflections and scattering.

Details on the position, conditions, and requirements can be found in the following document.

TIMEleSS Annual Meeting

TIMEleSS Annual Meeting 2020The 2020 TIMEleSS Annual Meeting was held online on 8-9 September 2020. Members from the Université de Lille (Julien Chantel, Jeffrey Gay, Estelle Ledoux, Sébastien Merkel), the Westfälische Wilhelms-Universität, Münster (Matthias Krug, Federica Rochira, Morvarid Saki, Angelo Pisconti, Christine Thomas), and the Deutsche GeoForschungsZentrum, Potsdam (Sergio Speziale) met for two half-days to discuss current advances and future plans.

The first day was dedicated to progress report by the PhD students. The second day followed by a scientific presentation by our guest Morvarid Saki and discussions on the geophysical implications of the results.

Despite the 2020 conditions, the TIMEleSS project is nicely moving forward. Students are reaching a stage when they fully interact with each other. The PIs can’t wait for next year with results and publications!

 

Beamtime at SOLEIL!

TIMEleSS team at the SOLEIL synchrotron during COVID-19We’ve made it! Despite delays due to COVID-19, we’ve made it to SOLEIL!

SOLEIL (“Sun” in French) is a synchrotron facility near Paris, France. The name SOLEIL is a backronym for Source optimisée de lumière d’énergie intermédiaire du LURE (LURE optimised intermediary energy light source), LURE meaning Laboratoire pour l’utilisation du rayonnement électromagnétique.

We are currently running an experiment at PSICHÉ (Pression Structure Imagerie par Contraste à Haute Énergie), a beamline dedicated to x-ray diffraction under extreme conditions (pressure-temperature) and to tomography by absorption contrast at high energy (20-50 keV), looking at phase transformation in deep Earth minerals.

Publication in The Conversation

New publication in Le manteau terrestres au laboratoire. New publication in The Conversation.the French edition of The Conversation!

The Conversation is a network of not-for-profit media outlets that publish news stories written by academics and researchers.

In this paper, TIMEleSS PI S. Merkel speaks about the Earth’s lowermost mantle, seismology, high pressure / high temperature mineral physics, and how phase transformations help us understanding deep Earth processes!

Seismology training for TIMEleSS members!

TIMEleSS February 2020 seismology trainingTIMEleSS members are in Münster!

TIMEleSS PI C. Thomas is hosting a seismology training for TIMEleSS students.

Participants include TIMEleSS students E. Ledoux, J. Gay, F. Rochira, M. Krug, and guests from WWU Münster Mineralogy and Seismology labs.

The training is the opportunity to move on to the next step in the TIMEleSS project: combining Mineral Physics and Seismology observations and try to say something about deep mantle processes!

Paper out in Nature Communications !

Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth's D″ layerFirst  publication for the TIMEleSS team: Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth’s D″ layer.

Bridgmanite is a magnesian-iron mineral ((Mg,Fe)SiO3) with a crystal structure that is not stable under ambient conditions. It forms about 660 kilometers below the surface of the Earth, and transforms to a new structure at even greater depth, approximately 2700 km depth, just above the Core-Mantle boundary.

During his PhD, C. Langrand, PhD student at the Université de Lille studied the kinetics of such transformation. It is fast on geological timescales: about 10 to 10,000 seconds, depending on pressure and temperature. Thanks to the collaborations in the TIMEleSS project, the authors realized that this includes the timescales of seismic waves. As such, seismic waves can trigger the transformation and, in turn, the transformation can amplify the seismic signal from D” seismic reflections.

These results from a collaboration between the Université de Lille, the université Clermont-Auvergne, the université de Lyon, the Westfälische Wilhelms-Universität, MünsterCNRS, and the PETRA III / DESY synchrotron source were published on 12 decembre 2019 in Nature Communications.

Full reference : C. Langrand, D. Andrault, S. Durand, Z. Konôpková, N. Hilairet, C. Thomas, S. Merkel, Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth’s D″ layer, Nature Communications, 10, 5680 (2019) [doi: 10.1038/s41467-019-13482-x].

TIMEleSS PI at AGU 2019

Centennial session at AGU 2019The fall meeting of the American Geophysical Union is the largest international Earth and space science meeting in the world with approximately 25000 attendees.

2019 is a special year that marks the Centennial for AGU. Monday dec. 9th was a celebration day for Earth Interior studies with a special Centennial session in which TIMEleSS PI S. Merkel was in charge of organizing and chairing part of the day.

Things return to a normal AGU now, with the usual layout for sessions and presentations. The TIMEleSS project will be presented on Thursday morning in session DI41C – A Deep Dive into Lowermost Mantle Processes. Please come by to see the state of our current research!

We are hiring!

Post-doc position on wave propagation in structures and microstructures at the University of Lille, France

The TIMEleSS project is looking for a post-doctoral fellow. The position is available for 1 year and extendable. The position is attached to the Earth and Planetary Materials group the Unité Matériaux et Transformations, at the Université de Lille, France, with strong collaborations with the Institute for Geophysics at the University of Münster.

The post-doc will be in charge of  simulating wave propagation in structures and microstructures with the aim of interpreting deep Earth seismic observables.

The candidate should have a strong background in deep Earth seismology and/or wave propagation in complex media and/or mineral physics and will be in charge of connecting mineral physics knowledge of phase transformations and microstructures in the Earth’s mantle to potential observations of seismic reflections and scattering.

Details on the position, conditions, and requirements can be found in the following document. The review of of applications will start by January 31st 2020 and will continue until the position is filled. The position is expected to start in the spring or the summer of 2020.

 

Lecture for junior high school students

Lecture for junior high school student

Students from the “Collège Val de la Sensée” in Arleux (Junior High School) are working on a project related to the famous Jules Vernes book Journey to the Center of the Earth.

On Nov. 25, 2019, they came to the Université de Lille for an example of a university class, as Otto Lidenbrock can teach in the Jules Vernes book. S. Merkel gave them a lecture on the Center of the Earth, as scientists view it and study it today, and how Jules Vernes visionary writings were both close and distant from today’s view of the Earth interior.