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.
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.
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.
September 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 ofTextures 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.
In 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!
Multigrain 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
The synchrotron guys of the TIMEleSS project met up for a datatron the second week of May 2019. During a TIMEleSS datatron, we all sit in a room and get moving on data processing from our recent synchrotron experiments!
The datatron was attented by M. Krug, E. Ledoux, and J. Gay, PhD students involved in the TIMEleSS project, S. Merkel, the PI for TIMEleSS. We also welcomed 3 guests during this week: J. Wright, from ID11 at ESRF, A. Dewaële from CEA, and M. Bykov from the Bayerisches Geoinstitut.
The next TIMEleSS datatron has not been planned yet but may happen later in 2019.
The workshop aims to bring together high-pressure researchers with different experimental expertise and to highlight the latest developments in high-pressure techniques across synchrotron beamlines.
S. Merkel gave a presentation entitled “In situ study of phase transformation mechanisms using multigrain crystallography“. The presentation was an opportunity to present the science at the foundation of the TIMEleSS project, its objectives, and some results.
The TIMEleSS team is holding its second training session on multigrain diffraction data processing. The session takes place on Feb 11-15 at the Université de Lille, in France. Participants (left to right on the image) include Julien Chantel, our guest Agnès Dewaele, Sébastien Merkel, Jeffrey Gay, Sergio Speziale, Estelle Ledoux, Matthias Krug, and Carmen Sanchez-Valle.
The session is an opportunity for all members to get trained in multigrain diffraction data processing but also to standardize our data workflow strategies.
This week, two of the TIMEleSS PI’s are attenting the Final Workshop of the CREEP ITN at the Ecole de Physique des Houches, in France. The workshop is held from 27 January to 1 February 2019 in the town of Les Houches, in the Chamonix valley.
The CREEP ITN is a EU funded project that proposed an interdisciplinary and multiscale approach to study the origin of rheological complexity in Earth and analogous materials and how it controls the dynamics of our planet, including natural and human-induced seismicity, and affects a large range of industrial applications, from energy production and waste storage to production of high-performance glasses. It included a number of partners, from academia and industry with over 10 PhD fellowships. More details can be seen at the CREEP ITN website.
The TIMEleSS project, its objectives, and some results were highlighted in a an hour long invited presentation regarding Phase transitions in the mantle by PI S. Merkel.
Matthias Krug and Frederica Rochira gave presentation in front of their institute in Münster.
Matthias presented his work on Jan 8th and Frederica on Jan 21st. These presentations were an opportunity for the students to display their works in front of their colleagues, get feedback, and new ideas for their project.
Estelle Ledoux and Jeff Gay presented they current work at the PhD student days for the UMET lab in Lille. The symposium is organized yearly in January.
This one-day meeting is an opportunity to discover the work of current PhD students and the evolution of research in the lab. It is an opportunity for exchanges between students and researchers, exchange ideas, and build strong future collaborations.
Federica Rochira and Matthias Krug presented posters at the Deep Earth Mini Symposium in Münster. The symposium was organized by TIMEleSS PI Tine Thomas.
This one-day meeting attracted an international and interdisciplinary group of deep Earth scientists, PhDs and Master students, with keynote talks given by Jennifer Jackson (Caltech), Jeroen Ritsema (University of Michigam) and Sebastian Rost (University of Leeds), and a poster session with wine and cheese.