Category: TIMEleSS news

On the Influence of Pressure, Phase Transitions, and Water on Large-Scale Seismic Anisotropy Underneath a Subduction Zone

Publications, TIMEleSS news

We have a new publication ! In his work published in AGU’s Geochemistry, Geophysics, Geosystems, J.K. Magali investigates the Influence of Pressure, Phase Transitions, and Water on Large-Scale Seismic Anisotropy Underneath a Subduction Zone.

In fact, subduction deep inside the Earth’s mantle causes the surrounding mantle to deform according to the movement and pressure exerted by the plates. This influences the alignment of minerals making up the mantle, which in turn, affects the speed and direction of seismic waves known as seismic anisotropy.

In this publication, we investigate the role of pressure in the upper mantle and water in the transition zone on large‐scale seismic anisotropy across a subduction zone. In the upper mantle, we show that the patterns of anisotropy at places where deformation is presumed to be large are affected by changes in pressure. In the transition zone, anisotropy tends to favor a wetter environment.

Want to know more ? The full reference is here : Magali, J. K., Thomas, C., Ledoux, E. E., Capdeville, Y., & Merkel, S. (2025). On the influence of pressure, phase transitions, and water on large-scale seismic anisotropy underneath a subduction zone. Geochemistry, Geophysics, Geosystems, 26, e2024GC011827. https://doi.org/10.1029/2024GC011827.

Federica Defended her thesis!

People news, PhD Theses, TIMEleSS news

PhD defense of F. Rochira, June 6, 2024On June 6, 2024, Federic Rochira defended her thesis! She presented her work for 30 minutes, followed by 60 minutes of oral examination, in front of an international committee composed of Tine Thomas as first examiner, Sebastian Rost (University of Leeds) as second examiner, and Alexander Kappes (University of Münster) as third examiner.

In her work, Federica investigated the presence of seismic structures in the Earth’s mantle and their effect on seismic wave paths, using a combination of seismic signals that are thought to travel along the predicted great circle path, between the source and the receiver, as well as signals traveling off the great circle path direction. To better constrain depth and location of mantle reflectors, she took into account directivity parameters of seismic signals, not yet widely used, as well as their traveltime.

Results show the advantages and necessity of using directivity information of seismic signals to detect regional-scale structures in the mantle associated with both subducted slabs and upwelling plumes, as well as mantle discontinuities. Ignoring the directional information, estimated location and depth of reflectors might be inaccurate and contribute to a misleading interpretation of mantle structures in terms of Earth’s dynamics and mineralogy.

She is now a Doctor of the University of Münster. Congratulations!

Seismic anisotropy of pyrolite in the Earth’s lower mantle

People news, Publications, TIMEleSS news

Depth Dependent Deformation and Anisotropy of Pyrolite in the Earth's Lower MantleYet another publication from the TIMEleSS team! Former TIMEleSS PhD student Jeff Gay has a new paper entitled Depth Dependent Deformation and Anisotropy of Pyrolite in the Earth’s Lower Mantle in the latest issue of Geophysical Research Letters.

Seismologists rely on observable data to construct models that describe the dynamic state of the Earth’s lower mantle. These models, however, require constraints such as mantle composition and material behavior at high pressures and temperatures, which can be provided through experimental mineral physics.

In this study, we use a high pressure devices and X-rays to impose deformation and image the state of our sample with increasing pressure and temperature. We are able to extract information of individual mineral grains within our assemblage, such as the number of grains per phase and their orientations.

Using this experimental data, we identify three regimes of grain orientations in bridgmanite in the lower mantle, corresponding to

  1. transformation from lower pressure phases,
  2. deformation below ~50 GPa,
  3. deformation above ~50 GPa.

With this information, we are able to make predictions about how seismic waves travel and behave based on the deformation state of the lower mantle.

Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flow

Publications, TIMEleSS news

Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flowFormer TIMEleSS post-doc John Keith Magali has a new publication: Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flow. The work was published in May 2024 in Geophysical Journal International.

In this work, John combines the team expertise in both mineral microstructures and seismic measurements to make predictions of seismic anisotropy development induced by mantle flow. In fact, observations of large-scale seismic anisotropy can be used as a marker for past and current deformation in the Earth’s mantle. Nonetheless, global features such as the decrease of the strength of anisotropy between ∼150 and 410 km in the upper mantle and weaker anisotropy observations in the transition zone remain ill-understood.

In this work, we integrate pressure-dependent microscopic flow properties in mantle minerals particularly olivine and wadsleyite into geodynamic simulations, compute the crystallographic preferred orientation and anisotropy in the upper mantle and upper transition zone, and apply a tomographic filter that accounts for finite-frequency seismic data, with the aim of providing mantle models comparable with seismic tomography observations.

Our results show that anisotropy observations in the upper mantle can be well understood by introducing gradual shifts in strain accommodation mechanism with increasing depths induced by a pressure-dependent plasticity model in olivine. Across the upper transition zone, our models predict reasonably low anisotropy, in agreement with observations.

These calculations show that, despite the relatively primitive geodynamic setup, models of plate-driven corner flows can be sufficient in explaining first-order observations of mantle seismic anisotropy. This requires, however, incorporating the effect of pressure on mineralogy and mineral plasticity models.

Publication on olivine-wadsleyite transformation microstructures

Publications, TIMEleSS news

In-situ study of microstructures induced by the olivine to wadsleyite transformation at conditions of the 410 km depth discontinuityThe TIMEleSS team has a new publication! In the December 2023 issue of American Mineralogist, former TIMEleSS student Estelle Ledoux present an In-situ study of microstructures induced by the olivine to wadsleyite transformation at conditions of the 410 km depth discontinuity.

The olivine-wadsleyite transformation is believed to occur at depths of about 410 km in the Earth, producing a major seismic discontinuity in this region of the Earth’s mantle. The mechanism of this phase transition controls the microstructures of the newly nucleated wadsleyite, the major phase of the upper part of the mantle transition zone, and thus impacts seismic observations in the region.

In this work, we study the microstructures produced by the olivine-wadsleyite transformation using in situ laboratory experiments at pressures and temperatures relevant for the mantle transition zone and measure the orientation and size distribution of individual sample grains using multigrain crystallography at synchrotron radiation sources. We find that the olivine to wadsleyite transformation is incoherent at the conditions of the mantle transition zone, and is probably dominated by nucleation of wadsleyite at grain boundaries of the parent olivine.

Thus, we expect that seismic anisotropy near 410 km would drop significantly due to the randomized lattice preferred orientation of newly nucleated wadsleyite induced by the incoherent transformation.

New publication in Geochemistry, Geophysics, Geosystems

TIMEleSS news

Deformation Mechanisms, Microstructures, and Seismic Anisotropy of Wadsleyite in the Earth’s Transition ZoneFormer TIMEleSS student Estelle Ledoux is the first author of Deformation Mechanisms, Microstructures, and Seismic Anisotropy of Wadsleyite in the Earth’s Transition Zone, published in gold open-access in AGU’s Geochemistry, Geophysics, Geosystems.

Rocks deep inside the Earth mantle are deforming plastically under the effect of mantle convection. In return, the way minerals accommodate deformation impacts the properties of the whole rock and controls mantle flow. The deformation mechanisms of upper mantle minerals have been studied extensively. The behavior of minerals found deeper in the Earth, however, still remains debated and poorly understood.

Wadsleyite is the high pressure polymorph of olivine and the major phase of the upper part of the mantle transition zone (MTZ) (at 410–520 km depth) and then is suspected to control the deformation of that region of the mantle. Investigations of deformation mechanisms in wadsleyite have been scarce and only made recently possible with in-situ measurements at relevant pressure and temperature.

Here, using in-situ deformation experiments, multigrain X-ray crystallography, literature results, and numerical simulations, we propose a new view of plastic deformation of wadsleyite in the Earth’s MTZ. We show that it will be strongly affected by both temperature and water content. We then provide models that could be used for the seismic detection of its anisotropic behavior and mapping mantle flow using seismic measurements.

Congratulations Estelle!

New publication in The Seismic Record

Publications, TIMEleSS news

On the Importance of Using Directional Information in the Search for Lower Mantle ReflectorsTIMEleSS PhD student Federica Rochira has a new paper! Along with TIMEleSS PI C. Thomas, Federica is the first author of On the Importance of Using Directional Information in the Search for Lower Mantle Reflectors. The paper is available in Gold Open Access in The Seismic Record.

In this work, Federica focuses on SS precursor signals. SS precursors are signals from S-waves reflected from structures in the Earth’s mantle. Those waves are interesting because they are sensitive to the local thermal and compositional structure deep in the Earth’s mantle.

She analyses how to model the location of the reflections of the wave and shows that a full account of the wave travel path can lead to differences of up to ∼150 km in regard to more simple geometrical calculations. These results hence indicate that the travel‐path deviations of SS precursors should be considered to avoid misinterpretation of mantle discontinuities and potentially reduce previously observed scatter in discontinuity depth.

Congratulations to Federica for the nice work!

First official release of the TIMEleSS-tools and first publication from outside users

Outreach, TIMEleSS news

The TIMEleSS-tools were developed in the course of the TIMEleSS project to streamline the processing of multigrain crystallography data from diamond anvil cell experiments. They were actively developed in the course of the project, guided by our needs for data processing, and used in all TIMEleSS publications involving multigrain X-ray diffraction. They are a set of python programs, open-source, under the terms of the GNU GENERAL PUBLIC LICENSE, Version 2, and part of the more general FABLE-3DXRD project.

After years of development, we finally reach the time for a 1.0.0 release. TIMEleSS-tools were uploaded to PyPI and will now be easily installable on any python distribution, by simply typing those three magical words pip install timeless-tools. The latest and most up-to-date version will remain at our TIMEleSS-tools github homepage, but this release is easier to install for starting users.

This official release also come with our first user publication! Robin Fréville, Agnès Dewaele, and co-authors published a Physical Review B paper on a Comparison between mechanisms and microstructures of α−γ, γ−ε, and α−ε−α phase transitions in iron on March 14, 2023. It is the first non-TIMEleSS published paper that relies on the TIMEleSS-tools. Congratulations to all!

New publication in Earth and Planetary Science Letters

Publications, TIMEleSS news

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

Activities, People news, PhD Theses, Special Events, Student events, TIMEleSS news

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

Publications, TIMEleSS news

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

Publications, TIMEleSS news

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

Conferences and workshops, TIMEleSS news

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

Experiments, TIMEleSS news

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

Experiments, Outreach, TIMEleSS news

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

Publications, TIMEleSS news

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

Publications, TIMEleSS news

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}⟨0−11⟩ 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

Publications, TIMEleSS news

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

Conferences and workshops, TIMEleSS news

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!