New 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.
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!
First 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].
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 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.
More to come soon with the TIMEleSS-tools developed at this occasion!
The TIMEleSS team is holding a first training session on multigrain diffraction data processing. The session takes place on June 21-23 at the Université de Lille, in France.
Participants (left to right on the image) include Julien Chantel, Sébastien Merkel, Sergio Speziale, Melissa Achorner, Estelle Ledoux, Ilya Kupenko, and Matthias Krug.
Members of the TIMEleSS project are spending a few days at the P02.2 beamline of the PETRA III synchrotron in Hamburg. Week-end will be busy and samples will get hot!
On the picture: Melissa Achorner (WWU Münster), Sergio Speziale (GFZ Potsdam), Estelle Ledoux (Univ. Lille), Matthias Krug (WWU Münster), Ilya Kupenko (WWU Münster), Julien Chantel (Univ. Lille), and Carmen Sanchez-Valle (WWU Münster).