ISTerre seminar

Effects of iron and volatile elements on the local structure and density of deep silicate melts

Monday 23 November 2026 - 14h00
Lucie Canet (Thesis defense) - ESRF
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Seismic observations of an ultra-low velocity zone at the Core-Mantle Boundary (2900 km depth) suggest the presence of a dense silicate melt layer. These melt layer could potentially represent a remnant basal magma ocean that was trapped after the metal-silicate differentiation and the partial crystallization of the mantle. Such a melt layer could be a potential reservoir for many incompatible geochemical elements and its existence would have important implications for the chemical and geodynamic evolution of the planet. While the potential existence of the basal magma ocean is supported by geodynamical modelling and geochemical analyses, it remains problematic to explain the stability of silicate melts at such conditions, that due to their lower density compared to the crystalline host rock, would rise to the planet’s surface.

To study the effect of Fe and volatiles elements on the structure and density of silicates melts at lower mantle conditions, we conduct in-situ synchrotron X-ray diffraction experiments in diamond anvil cells, on silicates glasses with compositions of (Mg1-xFex)SiO3 with x = 0, 0.1, 0.2, 0.4, and (Ca,Al,Na,Mg)SiO doped with CO2 and H2O, up to 135 GPa, at the beamline ID27 of the ESRF, in Grenoble. Data were acquired up to a very high Q-range (170 nm-1) using an incoming X-ray beam energy of 55 keV, enabling high real-space resolution and revealing distinct structural features in the pair distribution function at low pressure. Structural evolutions were followed qualitatively using the pair distribution functions, while density was extracted using a minimization of the figure of merit, and optimization of parameters such as the Q-range and a r cutoff value. The extracted data allow to identify the structural and density evolution of silicate glasses, as a function of pressure, iron and volatiles content.

Organizing team : Géodynamo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères