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In Situ Observations of Phase Changes in Shock Compressed Forsterite
Ist Teil von
Geophysical research letters, 2018-08, Vol.45 (16), p.8129-8135
Ort / Verlag
Washington: John Wiley & Sons, Inc
Erscheinungsjahr
2018
Quelle
Wiley-Blackwell Journals
Beschreibungen/Notizen
Shockwave data on mineral‐forming compounds such as Mg2SiO4 are essential for understanding the interiors of Earth and other planets, but correct interpretation of these data depends on knowing the phase assemblage being probed at high pressure. Hence, direct observations of the phase or phases making up the measured states along the forsterite Hugoniot are essential to assess whether kinetic factors inhibit the achievement of the expected equilibrium, phase‐separated assemblage. Previous shock recovery experiments on forsterite, which has orthorhombic space group Pbnm, show discrepant results as to whether forsterite undergoes segregation into its equilibrium phase assemblage of compositionally distinct structures upon shock compression. Here we present the results of plate impact experiments on polycrystalline forsterite conducted at the Dynamic Compression Sector of the Advanced Photon Source. In situ X‐ray diffraction measurements were used to probe the crystal structure(s) in the shock state and to investigate potential decomposition into periclase and bridgmanite. In contrast to previous interpretations of the forsterite shock Hugoniot, we find that forsterite does not decompose but instead reaches the forsterite III structure, which is a metastable structure of Mg2SiO4 with orthorhombic space group Cmc21.
Key Points
Chemical segregation of forsterite does not occur on the microsecond timescales
Kinetic effects determine the phases present on the forsterite Hugoniot up to 73 GPa