Sébastien Merkel

The annual meeting of the AGU attracts over 25,000+ scientists, educators, policymakers, journalists and communicators from over 100 countries in the broad field of Earth and space sciences. In December 2024, I was in Washington DC to attend the 2024 AGU Meeting and present the latest results of our European Research Council HotCores project.

New paper! Measurement bias in self-heating x-ray free electron laser experiments from diffraction studies of phase transformation in titanium, published in the Journal of Applied Physics recently. In this work, we focus on the physics of X-ray self-heating. X-ray heating is a common by-product of X-ray Free Electron Laser (XFEL) techniques that can affect targets, optics, and other irradiated materials. It is also useful in a new family of high pressure experiments that can reach the pressure and temperatures of planetary interiors. The work is a result of a collaboration of 31 laboratories over 7 countries and 3 continents, led by student O.B. Ball and R. S. McWilliams at the University of Edinburgh.

Participating to ICOTOM in Metz this week, the International Conference on Textures of Material, where world experts come to meet and discuss the latest advances in textures and microstructures of materials, with applications in multiple classes of materials, from metals to the deep Earth.

Yet another publication in two days! Zinc is a hcp structure metal, with a very large c/a ratio at ambient pressure, which then decreases and crosses √3 at ~10 GPa. As a consequence, twinning in zinc is unusual and can change in nature, from compressive to tensile, depending on the external pressure. Want to know more? Have a look at our ERC HotCores paper: Androgynous {10⁢-1⁢2} twin in zinc, published today in Physical Review Materials.

New publication from former PhD student Jeff Gay in Geophysical Research Letters: Depth Dependent Deformation and Anisotropy of Pyrolite in the Earth's Lower Mantle! This paper is from the TIMEleSS project, in which we investigated anisotropy induced by phase transformation and deformation using multigrain X-ray crystallography. If you want to learn about pyrolite in the deep mantle, have a look at the paper!

Publication of former TIMEleSS post-doc John Keith Magali: Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flow  in Geophysical Journal International. The papers focuses on a simple model of plate-driven corner flows and shows that, despite its simplistic formulation, it can explain first-order observations of mantle seismic anisotropy if one incorporates the effect of pressure on mineralogy and mineral plasticity models.

New publication in the Journal of Geophysical Research: Solid Earth. N. Hilairet writes about Stress balance in synthetic serpentinized peridotites deformed at subduction zone pressures. In this work, we analyze serpentinite rocks, which contain a variable amount of a weak minerals, including serpentine, and other stronger minerals and try to understand the effect of the percentage of the weak phase on the mechanical properties of the rock. The measurements are intended to help larger scale numerical models of interseismic processes that happen between earthquakes in subduction zones.

In case, you are wondering: you will not see me at the AGU Fall Meeting this year. I attended 22 out of the latest 26 AGU Fall Meeting. I felt that this year was a good one to take a break and not be travelling in December. Enjoy the meeting, I'm sure it will be great.

New publication in 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. We study the microstructures produced by the olivine-wadsleyite transformation using in situ laboratory experiments at pressures and temperatures relevant for the Earth's mantle transition zone, measure the orientation and size distribution of individual sample grains using multigrain crystallography, and find that the olivine to wadsleyite transformation is incoherent at the conditions of the mantle transition zone. 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 AGU’s Geochemistry, Geophysics, Geosystems by former TIMEleSS student Estelle Ledoux today: Deformation Mechanisms, Microstructures, and Seismic Anisotropy of Wadsleyite in the Earth’s Transition Zone. Wadsleyite is the high pressure polymorph of olivine and the major phase of the upper part of the mantle transition zone (at 410–520 km depth) and then is suspected to control the deformation of that region of the mantle. In this work, se use in-situ deformation experiments, multigrain X-ray crystallography, literature results, and numerical simulations to propose a new view of plastic deformation of wadsleyite in the Earth’s mantle transition zone. 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. More details online at https://doi.org/10.1029/2023GC011026.