A new high-pressure form of mg 2 sio 4 highlighting diffusionless phase transitions of olivine

Naotaka Tomioka, Takuo Okuchi

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    8 Citations (Scopus)

    Abstract

    High-pressure polymorphism of olivine (α-phase of Mg 2 SiO 4 ) is of particular interest for geophysicists aiming to understand the structure and dynamics of the Earth’s interior because of olivine’s prominent abundance in the upper mantle. Therefore, natural and synthetic olivine polymorphs have been actively studied in the past half century. Here, we report a new high-pressure polymorph, the ε*-phase, which was discovered in a heavily shocked meteorite. It occurs as nanoscale lamellae and has a topotaxial relationship with the host ringwoodite (γ-phase of Mg 2 SiO 4 ). Olivine in the host rock entrapped in a shock-induced melt vein initially transformed into polycrystalline ringwoodite through a nucleation and growth mechanism. The ringwoodite grains then coherently converted into the ε*-phase by shear transformation during subsequent pressure release. This intermediate metastable phase can be formed by all Mg 2 SiO 4 polymorphs via a shear transformation mechanism. Here, we propose high-pressure transformations of olivine that are enhanced by diffusionless processes, not only in shocked meteorites but also in thick and cold lithosphere subducting into the deep Earth.

    Original languageEnglish
    Article number17351
    JournalScientific reports
    Volume7
    Issue number1
    DOIs
    Publication statusPublished - 2017

    ASJC Scopus subject areas

    • General

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