Tag: publication

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!

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.

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]

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 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]

Publication in the European Journal of Mineralogy!

Activities, Publications

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].

Paper out in Nature Communications !

Publications, TIMEleSS news

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, Münster,  CNRS, 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].