1:45 PM - 2:00 PM
[SCG44-07] Crystallographic preferred orientation of MgO in the lower mantle inferred from high-temperature, high-pressure large-strain deformation experiments using rDAC
The crystallographic preferred orientation (CPO) of lower mantle minerals is key to understanding the structure and dynamics of the lower mantle. The seismic observations of the lower mantle have found the localized seismic anisotropy. However, the cause of its formation is not well understood. For instance, the candidates of S-wave anisotropy (VSH>VSV) around Large low-shear-velocity province (LLSVP) are CPO induced by deformation of the lower mantle minerals such as post-perovskite, ferropericlase, and bridgmanite, but it is still controversial. One of the reasons why this discussion remains unresolved is that there are technical difficulties in conducting quantitative deformation experiments under lower mantle conditions. In this study, we performed large strain deformation experiments on periclase (MgO) using the recently developed rotational diamond anvil cell (rDAC) and discuss the CPO and slip system that develop in the lower mantle.
Torsional deformation experiments on periclase were conducted using rDAC at BL47XU, SPring-8 (Pressure: atmospheric pressure–80 GPa, Temperature: 300–973 K, Strain: 61–293 %, Strain rate: 10-5–10-4 /s). The sample was put into the tungsten gasket and pressurized by rDAC, and heated by the near-infrared focused heating system (halogen lamps and reflectors) under vacuum conditions. Debye-Scherrer rings (Debye rings) were obtained by in-situ XRD measurements during the deformation experiments. The differential stress and development of CPO on periclase were determined from the obtained Debye rings.
Our experimental results indicated the temperature dependence in the transition of the slip plane from {110} to {100} under high-pressure conditions. The results were consistent with the slip plane reported from previous studies of the first-principles calculation (Amodeo et al., 2012) and compression experiments of Immoor et al. (2018) that utilized the conventional DAC. However, the temperature and pressure conditions of its transition was clearly different. The slip system transitions inferred from our results suggest that the {1 0 0} is a dominant slip plane throughout the lower mantle. The CPO of the periclase developed in our deformation experiments could reproduce the S-wave anisotropy observed around the LLSVP in the lowermost mantle.
Torsional deformation experiments on periclase were conducted using rDAC at BL47XU, SPring-8 (Pressure: atmospheric pressure–80 GPa, Temperature: 300–973 K, Strain: 61–293 %, Strain rate: 10-5–10-4 /s). The sample was put into the tungsten gasket and pressurized by rDAC, and heated by the near-infrared focused heating system (halogen lamps and reflectors) under vacuum conditions. Debye-Scherrer rings (Debye rings) were obtained by in-situ XRD measurements during the deformation experiments. The differential stress and development of CPO on periclase were determined from the obtained Debye rings.
Our experimental results indicated the temperature dependence in the transition of the slip plane from {110} to {100} under high-pressure conditions. The results were consistent with the slip plane reported from previous studies of the first-principles calculation (Amodeo et al., 2012) and compression experiments of Immoor et al. (2018) that utilized the conventional DAC. However, the temperature and pressure conditions of its transition was clearly different. The slip system transitions inferred from our results suggest that the {1 0 0} is a dominant slip plane throughout the lower mantle. The CPO of the periclase developed in our deformation experiments could reproduce the S-wave anisotropy observed around the LLSVP in the lowermost mantle.