TIMEleSS

The TIMEleSS project aims at studying interfaces in the Earth’s mantle combining observations from seismology, mineral physics experiments, microstructures, and wave propagation modeling. It is supported through a bilateral grant, from the ANR in France and the DFG in Germany. The project is led by Sébastien Merkel and Nadège Hilairet at the Université de Lille, Christine Thomas and Carmen Sanchez-Valle from the Westfälische Wilhelms-Universität, Münster, and Sergio Speziale from the Deutsche GeoForschungsZentrum, Potsdam.

Project launch: March 2018
Duration: 36 months, extended until December 2022
Total ANR-DFG funding: 700 000 €

The active research period of TIMEleSS is now over, but we are still working on our datasets and publications so stay tuned for more!

Latest news

Seismic anisotropy of pyrolite in the Earth’s lower mantle

9 June 2024 | Posted in People news, Publications, TIMEleSS news

Depth Dependent Deformation and Anisotropy of Pyrolite in the Earth's Lower MantleYet another publication from the TIMEleSS team! Former TIMEleSS PhD student Jeff Gay has a new paper entitled Depth Dependent Deformation and Anisotropy of Pyrolite in the Earth’s Lower Mantle in the latest issue of Geophysical Research Letters.

Seismologists rely on observable data to construct models that describe the dynamic state of the Earth’s lower mantle. These models, however, require constraints such as mantle composition and material behavior at high pressures and temperatures, which can be provided through experimental mineral physics.

In this study, we use a high pressure devices and X-rays to impose deformation and image the state of our sample with increasing pressure and temperature. We are able to extract information of individual mineral grains within our assemblage, such as the number of grains per phase and their orientations.

Using this experimental data, we identify three regimes of grain orientations in bridgmanite in the lower mantle, corresponding to

  1. transformation from lower pressure phases,
  2. deformation below ~50 GPa,
  3. deformation above ~50 GPa.

With this information, we are able to make predictions about how seismic waves travel and behave based on the deformation state of the lower mantle.

Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flow

13 May 2024 | Posted in Publications, TIMEleSS news

Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flowFormer TIMEleSS post-doc John Keith Magali has a new publication: Pressure-dependent large-scale seismic anisotropy induced by non-Newtonian mantle flow. The work was published in May 2024 in Geophysical Journal International.

In this work, John combines the team expertise in both mineral microstructures and seismic measurements to make predictions of seismic anisotropy development induced by mantle flow. In fact, observations of large-scale seismic anisotropy can be used as a marker for past and current deformation in the Earth’s mantle. Nonetheless, global features such as the decrease of the strength of anisotropy between ∼150 and 410 km in the upper mantle and weaker anisotropy observations in the transition zone remain ill-understood.

In this work, we integrate pressure-dependent microscopic flow properties in mantle minerals particularly olivine and wadsleyite into geodynamic simulations, compute the crystallographic preferred orientation and anisotropy in the upper mantle and upper transition zone, and apply a tomographic filter that accounts for finite-frequency seismic data, with the aim of providing mantle models comparable with seismic tomography observations.

Our results show that anisotropy observations in the upper mantle can be well understood by introducing gradual shifts in strain accommodation mechanism with increasing depths induced by a pressure-dependent plasticity model in olivine. Across the upper transition zone, our models predict reasonably low anisotropy, in agreement with observations.

These calculations show that, despite the relatively primitive geodynamic setup, models of plate-driven corner flows can be sufficient in explaining first-order observations of mantle seismic anisotropy. This requires, however, incorporating the effect of pressure on mineralogy and mineral plasticity models.

Publication on olivine-wadsleyite transformation microstructures

10 December 2023 | Posted in 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

16 November 2023 | Posted in 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!

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Partners

Partner institutions

Université de Lille CNRS   Westfälische Wilhelms-Universität Münster  Deutsche GeoForschungsZentrum

Participating laboratories

Unité Matériaux et Transformations, Université de Lille Institut für Geophysik, Universität Münster
Institut für Mineralogie, Universität Münster Chemistry and Physics of Earth Materials, GFZ

Funding bodies

 

Agence Nationale de la Recherche Deutsche Forschungsgemeinschaft  Projet financé par l'ANR