In situ X-ray diffraction of silicate liquids and glasses under dynamic and static compression to megabar pressures

G Morard and JA Hernandez and M Guarguaglini and R Bolis and A Benuzzi- Mounaix and T Vinci and G Fiquet and MA Baron and SH Shim and B Ko and AE Gleason and WL Mao and R Alonso-Mori and HJ Lee and B Nagler and E Galtier and D Sokaras and SH Glenzer and D Andrault and G Garbarino and M Mezouar and AK Schuster and A Ravasio, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 117, 11981-11986 (2020).

DOI: 10.1073/pnas.1920470117

Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core-mantle boundary. Here we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO3 glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth's core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.

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