Séminaire/Seminar - Planetary differentiation studied by in situ time-resolved X-ray diagnostics - Guillaume Morard

Vendredi 8 septembre 2023 à 14 h

IMPMC - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-23, 4e étage, salle 401 

Guillaume Morard, chercheur à l'ISTerre (Grenoble)

Abstract

Understanding the mechanisms and chemistry in play in the deep Earth without direct rock samples is a strong motivation to study the physical properties and phase relations of materials constituting our planetary interior. 

As it formed, the Earth experienced a molten state as a result of large impacts, accretional energy and the contribution of short-lived radio-nuclides. This fully molten stage in planetary accretion, the so-called Magma Ocean (Tonks and Melosh, 1993), has strong implications for the subsequent evolution of the planet, from internal processes such as mantle convection and plate tectonics, up to the distribution of chemical elements, and notably the distribution of volatiles between the atmosphere and the interior of the planet (Elkins-Tanton, 2012), and may be different on Venus or other planets. The Earth then formed a differentiated structure, with a rocky mantle and metallic core, which is common among Earth-like planets and asteroids in the solar system. Past differentiation, as the solidification process starts upon cooling, the mechanical properties of the solid in coexistence with the liquid are required to constrain the heat dissipation related to orbital resonances, core-mantle differentiation mechanisms, and the long-term evolution of a mantle heat over the core

Conventional static compression using Diamond Anvil Cell recently allowed in situ X-ray diagnostics for samples over 500 GPa (Dewaele et al., 2018), albeit at ambient temperature. In addition, dynamic compression driven by high-power lasers easily reach pressures over 500 GPa and temperature over 10 000 K for geomaterials. Until recently, however, conventional diagnostics for laser-driven shock compression experiments were limited to optical measurement of pyrometry and velocimetry. The advent of new X-ray sources, such as Free Electron Laser (FEL) or upgraded synchrotrons (such as the Extremely Brilliant Source (EBS) upgrade at ESRF available since September 2020), opens a favorable window to develop new diagnostics or rethink the existing experimental programs. Indeed, the high brilliance of these new X-ray sources offers the possibility of unprecedented time-resolved in situ X-ray diagnostics, allowing to track high P-T processes at the nanosecond (ns) to microsecond (µs) timescales. Preventing chemical migration, contamination or grain growth, these diagnostics can now be coupled with dynamic or static compression, to unravel the structure and mechanical properties of geomaterials over a wide density range. 

References

Dewaele, A., Loubeyre, P., Occelli, F., Marie, O., Mezouar, M., 2018. Toroidal diamond anvil cell for detailed measurements under extreme static pressures. Nat. Commun. 9, 1–9. https://doi.org/10.1038/s41467-018-05294-2

Elkins-Tanton, L.T., 2012. Magma Oceans in the Inner Solar System. Annu. Rev. Earth Planet. Sci. 40, 113–139. https://doi.org/10.1146/annurev-earth-042711-105503

Tonks, W.B., Melosh, H.J., 1993. Magma ocean formation due to giant impacts. J. Geophys. Res. Planets 98, 5319–5333. https://doi.org/10.1029/92JE02726