New publication 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 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

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 Conversation

New publication in Le manteau terrestres au laboratoire. New publication in The Conversation.the French edition of The Conversation!

The Conversation is a network of not-for-profit media outlets that publish news stories written by academics and researchers.

In this paper, TIMEleSS PI S. Merkel speaks about the Earth’s lowermost mantle, seismology, high pressure / high temperature mineral physics, and how phase transformations help us understanding deep Earth processes!

Paper out in Nature Communications !

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, MünsterCNRS, 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].

TIMEleSS PI at AGU 2019

Centennial session at AGU 2019The fall meeting of the American Geophysical Union is the largest international Earth and space science meeting in the world with approximately 25000 attendees.

2019 is a special year that marks the Centennial for AGU. Monday dec. 9th was a celebration day for Earth Interior studies with a special Centennial session in which TIMEleSS PI S. Merkel was in charge of organizing and chairing part of the day.

Things return to a normal AGU now, with the usual layout for sessions and presentations. The TIMEleSS project will be presented on Thursday morning in session DI41C – A Deep Dive into Lowermost Mantle Processes. Please come by to see the state of our current research!

Frederica Rochira presents her work at EGU

Frederica Rochira at EGU 2019 in Vienna

Frederica Rochira was at the EGU General Assembly 2019 in Vienna. EGU brings together geoscientists to one meeting covering all disciplines of the Earth, planetary and space sciences. The meeting is held yearly in Vienna, Austria, and, in 2019, it was attended by 16,273 scientists from 113 countries.

Frederica Rochira presented her works entitled Detecting structures in the mid mantle using out-of-plane signals in the multidisciplinary session Dynamics of the mantle in the Earth and planetary bodies: from magma oceans to the present day.

The session, co-organized by TIMEleSS members, included four oral presentations on Thursday as well as 12 PICO presentations early afternoon on Friday. The session was an opportunity for scientists of various fields of geosciences (seismology, geodynamics, mineral physics) to present the results of her works and discuss their implications for understanding the dynamics of mantles, on Earth and other planetary bodies.

TIMEleSS PI giving invited lecture in Les Houches

CREEP Final Workshop Ecole de Physique des Houches (F) 27 January – 1 February 2019

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.

PhD student day in Lille

Jeff Gay and Estelle Ledoux at PhD student days at UMET in Lille in 2019

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.

The full program of the symposium can be found online in the following document.

Deep Earth Mini Symposium at WWU Münster

Federica Rochira and Matthias Krug at the Deep Earth Mini Symposium in Münster in December 2018

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.

The full program of the symposium can be found online in the following document.

TIMEleSS PI begins its term at the American Geophysical Union Council

The American Geophysical Union held elections to replace its council members earlier in 2018. S. Merkel, one of the TIMEleSS PI’s, was elected for the Mineral and Rock Physics section of AGU.

He will begin is 4-year term as a Council member for AGU on January 1st, 2019. As a member of the Council, representing the broad spectrum of AGU members,  he will oversee the scientific affairs of AGU. The Council is responsible for the scientific affairs of AGU and plays three distinct roles: forming science policy, generating and deliberating science-related ideas, and advising on science and member issues.

He will also endorse the role of president-elect for the Mineral and Rock Physics section in 2019-2020 before becoming the section president for a 2-years term in 2021-2022.

Lecture for high school teachers

Forum "Enseigner les Géosciences", Lille, Octobre 2018La convertion dans le manteau

One of the TIMEleSS PI’s gave a general lecture on Mantle Convection this week.

The French geological society meeting (Réunion des Sciences de la Terre) was held in Lille between Oct 22 and Oct 26, 2018, and included a workshop on Teaching Earth Science in High Schools dedicated to high school teachers in Northern France.

The workshop included a day of scientific presentations during which S. Merkel gave a class on Mantle Convection and a day of field trip. The workshop was also a nice and rare opportunity for high school teachers in Northern France to be in contact with international research in their region.