Liquid silicates under extreme conditions : implications for magma oceans differentiation

4 to 6 months (March-July 2022) ; based at ESRF, Grenoble

Contexte du stage
During its early stage, our planet experienced a molten state as a result of large impacts, accretional energy and the contribution of short-live radio-nuclides. The resulting magma ocean, with (Mg,Fe)SiO3 as an archetypical composition, had major implications in the Earth’s evolution ranging from the formation of the core and its interaction with the mantle, to mantle convection and plate tectonics, up to the distribution of chemical elements, and notably the distribution of volatiles between the atmosphere and the interior [1].
However, several technical issues limit our current understanding of dense silicates melts. Static compression studies in large volume presses allow to produce silicate liquids under well-controlled conditions but are limited, up to now, to 25 GPa and less than 3000 K. The recent combination of dynamic compression techniques (laser drives and plate impacts) and ultrafast X-ray probes on X-ray free electron laser and 4th generation synchrotrons allows to get structural and chemical insights on these liquids. In previous studies, we investigated the properties of pure MgSiO3 glasses and melts under both static and dynamic compression [2,3]. The logical next step is therefore exploring the properties of more realistic high-pressure Fe-bearing silicates melts forming magma oceans.
The environment of Fe atoms as well as their oxidation states in liquid and glassy ferro-magnesian silicates will be probed using X-ray Absorption Spectroscopy. Tracking the Fe oxidation state as a function of pressure and temperature in liquid silicates is important to understand the potential Fe disproportionation, where Fe2+ evolves toward Fe3+ and metallic iron as shown in the solid phase [4].

Objectifs du stage
The recent availability of an high power laser on the XAS beamline ID24 at ESRF [5] will make it a unique place to perform such experiments coupling energy dispersive XAS and laser-driven compression.
The aim of this internship is to participate to the targets’ elaboration for dynamic compression experiments, to contribute to a large international consortium using state-of-the-art European facility and to perform unique dataset analysis on X-ray Absorption Spectroscopy of Fe-bearing molten silicates under extreme Pressure-Temperature conditions.
The internship will be based at ESRF, on the ID24 beamline, and co-supervised by Jean-Alexis Hernandez (ESRF), Guillaume Morard (ISTerre, Grenoble) and Alessandra Ravasio (LULI, Ecole Polytechnique) for a duration of 4 to 6 months (March-July 2022).

Références bibliographiques
[1] Wood, B. J., & Halliday, A. N. (2005). Nature, 437, 1345-1348.
[2] Hernandez, J. A., et al. (2020). Geophysical Research Letters, 47(15), 1–9.
[3] Morard, G., et al. (2020). Proceedings of the National Academy of Sciences, 117(22), 11981–11986.
[4] Fialin, M., et al. (2009). Physics and Chemistry of Minerals, 36(4), 183-191.
[5] Torchio, R., et al. (2016). Scientific reports, 6(1), 1-8.