New publication in Earth and Planetary Science Letters

Gay et al, Transformation microstructures in pyrolite under stress: Implications for anisotropy in subducting slabs below the 660 km discontinuity (2023) Earth and Planetary Science LettersNew year, and new publication for the TIMEleSS team! Former timeless PhD student Jeff Gay is the first author of Transformation microstructures in pyrolite under stress: Implications for anisotropy in subducting slabs below the 660 km discontinuity, published in the February 15, 2023, issue of Earth and Planetary Science Letters. The publication is a result of a collaboration between partners at the Université de Lille (J. Gay, E. Ledoux, J. Chantel, S. Merkel), WWU Münster (N. Krug, C. Sanchez-Valle) with measurements at the Deutsches Elektronen-Synchrotron (A. Pakhomova, H.-P. Liermann).

The ‘660’ discontinuity marks the boundary between the upper and lower mantle and is located 660 km below our feet. The is discontinuity often associated with a phase transitions in pyrolite, a model rock composition for the Earth’s mantle. In addition, there are ubiquitous reports of seismic anisotropy below the ‘660’ which are difficult to explain from a mineralogical point of view.

In this study, we implement multigrain crystallography X-ray diffraction in the laser-heated diamond anvil cell in order to track microstructures induced by phase transitions at the pressure and temperature conditions of the discontinuity, around 24 GPa and 1900 K. Before the onset of transformation, pyrolite minerals such as garnet and ringwoodite are isotropic and do not contribute to seismic anisotropy.  After the transformation, bridgmanite, the most abundant mineral in the Earth, displays a strong preferred orientation, which we attribute to growth under stress. Other minerals such as davemaoite and ferropericlase are also considered.

The results are used to model anisotropy in a subducting slab, with a prediction of no anisotropy above the ‘660’ and up to 1.28% (0.08 km/s) shear wave splitting below the ‘660’ and provide details on how detailed wave forms can be used to understand the geometry of stress at those depths.

PhD Thesis Defence for Jeffrey Gay

PhD Thesis Defense, Jeffrey Gay, Nov 2022A new PhD defense for the TIMEleSS project!

On Nov 24th, 2022, Jeffrey Gay defended his thesis entitled Microstructures and anisotropy of pyrolite in the Earth’s lower mantle: insights from high pressure/temperature deformation and phase transformation experiments at the Université de Lille.

The PhD committee was composed of

  • Motohiko Murakami, ETH Zürich, Rapporteur
  • Denis Andrault, Univ. Clermont Auvergne, Rapporteur
  • Ana Ferreira, Univ. College London, Examinateur
  • Angelika Rosa, European Synchrotron Radiation Facility, Examinateur
  • Huges Leroux, Univ. Lille, Examinateur and President
  • Sébastien Merkel, Univ. Lille, PhD Advisor

Jeff presented his work for 45 minutes, followed by an hour of discussion with the committee. After deliberation, the committee decided to award the Doctoral Degree to Jeffrey Gay.

Congratulations Jeff!

Yet a second publication in Geochemistry, Geophysics, Geosystems: coesite-stishovite transition and the X-discontinuity

Textures Induced by the Coesite-Stishovite Transition and Implications for the Visibility of the X-Discontinuity, by M. KrugSeptember 2022 is a good month for the TIMEleSS project: we have a second publication in the journal Geochemistry, Geophysics, Geosystems by the American Geophysical Union! TIMEleSS PhD student Matthias Krug is the first author of Textures induced by the coesite-stishovite transition and implications for the visibility of the X-discontinuity. The work is a result of the TIMEleSS collaboration and involves Morvarid Saki, Estelle Ledoux, Jeffrey P. Gay, Julien Chantel, Anna Pakhomova, Rachel Husband, Arno Rohrbach, Stephan Klemme, Christine Thomas, Sébastien Merkel, and Carmen Sanchez-Valle as co-authors.

Coesite is a high pressure polymorph of SiO2 formed from quartz at pressures above 2 to 3 GPa. In the Earth coesite is formed at approximately 70 km depth or more, depending on the exact temperature conditions. At pressures of 8 to 11 GPa, corresponding to approximately 250 to 300 km, yet another transformations occurs and coesite becomes stishovite. Stishovite was discovered experimentally in 1961 by Sergey M. Stishov and later found in Meteor Crater in Arizona. In parallel, seismic studies report widespread occurrence of velocity anomalies at ∼300 km depth in the Earth’s mantle, whose origin is still not well understood. In this work, Matthias Krug performed experiments to check whether the phase transition in SiO2 from coesite to stishovite could explain these observations and the reasons for the widespread but not global occurrence of the X-discontinuity at 300 km depth.

We reproduced the pressure and temperature conditions at 300 km depth in the laboratory and applied an advanced X-ray diffraction technique to monitor changes in the orientation of grains (i.e., microstructure) in the sample across the transition. We observe that the randomly oriented grains in the low-pressure phase coesite display strong preferred orientation when transformed to stishovite after the transition. In order to relate the experimental observations of grain orientations to the seismic detection of the X-discontinuity, we then computed the effect of grain orientations on the propagation of seismic waves and the velocity changes across the phase transitions. We conclude that 10 – 50 vol.% of crustal rocks embedded in the mantle are needed to explain the observed anomalies and propose that the intermittent observation of this anomaly is related to the seismic sampling strategy rather than to lack of silica anomalies (and hence the absence of the transition) in some specific mantle settings.

New publication in Geochemistry, Geophysics, Geosystems

D" Reflection Polarities Inform Lowermost Mantle MineralogyThe TIMEleSS project has a new paper in September 2022! TIMEleSS PI C. Thomas is the first author of a publication entitled D” Reflection Polarities Inform Lowermost Mantle Mineralogy in the journal Geochemistry, Geophysics, Geosystems from the American Geophysical Union.

In this work, C. Thomas and co-authors L. J. Cobden, A. R. T. Jonkers investigate the polarities of seismic waves reflecting at structures in the Earth’s mantle and how they can be affected by seismic velocity changes at the interface. For the lowermost mantle reflector, a velocity increase generates a polarity that is the same for the main wave and the core-reflected wave. If, however, the percentage change of the velocity of the S wave increases at least three times as much as that of the P wave velocity (expressed as the R-value, the ratio dVs/dVp), the polarity of the D”-reflected PdP wave changes polarity, becoming opposite to both the main P wave and the reflection from the core-mantle boundary below it.

In the publication, they analyze sets of 1 million models with variable compositions of mantle material and mid-ocean ridge basalt and use an advanced statistical method to identify those combinations of minerals that produce large positive R-values. They distinguish four cases and find that previous explanations for three of these cases concur with our analysis. For regions where velocities decrease over the D” reflector, the analysis shows that enrichment with the lower-mantle mineral bridgmanite is responsible for the observed polarity behavior of P and S waves. This means that for regions such as large low-velocity anomalies in the lowermost mantle, primitive or bridgmanite-enriched material is the preferred explanation.

For more details, have a look at the full publication: C. Thomas, L. J. Cobden, A. R. T. Jonkers, D” Reflection Polarities Inform Lowermost Mantle Mineralogy, Geochemistry, Geophysics, Geosystems, 23, e2021GC010325 [doi: 10.1029/2021GC010325]

Study of the Earth’s Deep Interior

View from the rooftop of ETH ZürichSEDI is an international scientific organization dedicated to the Study of the Earth’s Deep Interior. The ultimate goal of SEDI is an enhanced understanding of the past evolution and current thermal, dynamical and chemical state of the Earth’s deep interior and of the effect that the interior has on the structures and processes observed at the surface of the Earth.

The 2022 Symposium of SEDI is being held in Zurich, Switzerland, from 11th to 15th of July, 2022. TIMEleSS participants C. Thomas, S. Merkel, and J-K Magali are in to discuss their latest results and understanding of deep Earth processes.

TIMEleSS presentations include

  • On the hunt for seismic anisotropy in the lower-mantle from the crystallographic preferred orientation of bridgmanite aggregates induced by large-scale flow, by John Keith Magali et al.
  • Microstructures and anisotropy in pyrolite at lower mantle pressures and temperature, by Jeffrey P. Gay, Estelle Ledoux, Matthias Krug, Julien Chantel, Carmen Sanchez-Valle, Sébastien Merkel
  • Seismic anisotropy due to textures above and below the 410 km discontinuity, by Morvarid Saki et al

See you in Zürich for a wonderful week!

TIMEleSS Tools for Multigrain X-ray Diffraction

TIMEleSS toolsIn addition to contributing the TIMEleSS Multigrain Wiki, TIMEleSS members also released a set of python and matlab utilities to process, analyze, plot, and understand multigrain X-ray diffraction data. All are released under an open-source licence at GitHub on the TIMEleSS-tools and TIMEleSS-Matlab repositories.

TIMEleSS-tools include various utilities to process images, clean up parasite signals on the X-ray diffraction images, manage your peaks and grains, and post-process the output of the various multigrain XRD sofwares.

TIMEleSS-Matlab are MTEX functions one can use to represent grain orientations in pole or inverse pole figures with efficient and intuitive color scales.

Enjoy, and do not hesitate to push any improvement you might make!

TIMEleSS Multigrain Wiki

TIMEleSS Multigrain WikiMultigrain X-ray diffraction (sometimes called 3D-XRD or HEDM depending on communities) allows characterizing hundreds of crystals in a polycrystalline material. It has been adapted to diamond anvil cell experiments for the investigation of materials under high pressure and high temperature. The method lies at the core of the experimental portion of the TIMEleSS project. We use it to characterize transformation and deformation microstructures in mantle minerals.

Multigrain X-ray diffraction can be hard to learn and implement. Hence, along the course of the project, timeless members documented their procedures for processing such data in an online documentation: the TIMEleSS Multigrain Wiki.

We are now finished with our rounds of experiments, data has been processed, and results are being submitted for publication, so it is time to give back to the community! The TIMEleSS Multigrain Wiki has been accessible for years to who knew the URL. Now the link is public and should be easy to find with your best search engines. Please use it, enjoy it, and do not hesitate to contact us if you want to contribute and suggest corrections

This wiki, among with other outputs, was used as a basis for the creation of the Commission on Diffraction Microstructure Imaging of the International Union of Crystallography. This new Commission on Diffraction Microstructure Imaging was established at the Prague General Assembly in August 2021 and TIMEleSS PI S. Merkel is one of the founding members for the application.

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!

PhD Thesis Defence for Estelle Ledoux

PhD Defence Estelle Ledoux, Oct 20, 2021A new PhD defense for the TIMEleSS project!

On Oct 20th, 2021, Estelle Ledoux defended her thesis entitled Microstructures de transformation et déformation dans le manteau terrestre : application au périclase et à la wadsleyite at the Université de Lille.

The PhD committee was composed of

  • Jannick Ingrin, Univ. Lille, President
  • Sylvie Demouchy, Univ. Montpellier II, Rapporteur
  • Daniele Antonangeli, Sorbonne Univ., Rapporteur
  • Jonathan Amodeo, Univ. Lyon 1, Examinateur
  • Isabelle Daniel, Univ. Claude Bernard Lyon 1, Examinateur
  • Sébastien Merkel, Univ. Lille, PhD Advisor
  • Damien Jacob, Univ. Lille, PhD Advisor

Estelle presented her work for 45 minutes, followed by an hour of discussion with the committee. After deliberation, the committee decided to award the Doctoral Degree to Estelle Ledoux.

Congratulations Estelle!

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!