Search for: All records

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 microstructural 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. 

Understanding spatial distribution of phases as well as dynamics across phase transformations in the lower mantle are crucial understanding the evolution of the Earth’s interior. Studies at high pressures and temperatures have previously relied on powder diffraction or single crystal methods which have limitations in spatial resolution during dynamic processes. Here we apply the novel multigrain crystallography technique at high pressure and temperature in a laser heated diamond anvil cell (LH-DAC) to study the formation of the Earth’s most abundant mineral bridgmanite MgSiO3 from a natural olivine sample. We constrain the twinning relationship in the bridgmanite phase at high pressure with grain-size resolution as well as evidence for an interconnected network formed by the weaker ferropericlase phase which could contribute to slab stagnation and plume deflection