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Using multigrain crystallography to explore the microstructural evolution of the α-olivine to γ-ringwoodite transformation and ε-mg2sio4 at high pressure and temperature

  • Author(s): Chandler, B;
  • Devoe, M;
  • Kunz, M;
  • Wenk, HR
  • et al.
Abstract

The introduction of multigrain crystallography (MGC) applied in a laser-heated diamond anvil cell (LH-DAC) using synchrotron X-rays has provided a new path to investigate the microstruc-tural evolution of materials at extreme conditions, allowing for simultaneous investigations of phase identification, strain state determination, and orientation relations across phase transitions in a single experiment. Here, we applied this method to a sample of San Carlos olivine beginning at ambient conditions and through the α olivine → γ-ringwoodite phase transition. At ambient temperatures, by measuring the evolution of individual Bragg reflections, olivine shows profuse angular streaking consistent with the onset of yielding at a measured stress of ~1.5 GPa, considerably lower than previously reported, which may have implications for mantle evolution. Furthermore, γ-ringwoodite phase was found to nucleate as micron to sub-micron grains imbedded with small amounts of a secondary phase at 15 GPa and 1000◦C. Using MGC, we were able to extract and refine individual crystallites of the secondary unknown phase where it was found to have a structure consistent with the ε-phase previously described in chondritic meteorites.

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