[S-CG62] Rheology, fracture and friction in Earth and planetary sciences

[SCG62-13] CPO of the Earth’s lower mantle minerals in situ at high pressure-temperature conditions inferred from torsional deformation experiments using a rDAC

*Bunrin Natsui¹, Shintaro Azuma¹, Keishi Okazaki^2,3, Kentaro Uesugi⁴, Masahiro Yasutake⁴, Saori Kawaguchi⁴, Steeve Gréaux⁵, Ryuichi Nomura⁶, Kenji Ohta¹ (1.Institute of Science Tokyo, 2.Hiroshima University, 3.Japan Marine Science and Technology Center, 4.Japan Synchrotron Radiation Research Institute, 5.Ehime University, 6.Kyoto University)

Keywords:Lower mantle, Ferropericlase, Deformation Experiment, X-ray diffraction, Crystallographic preferred orientation

Seismic tomography has shown that Large Low Shear Velocity Provinces (LLSVPs) with seismic anisotropy extend from the mid-lower to the lowest mantle beneath the African and Pacific. Seismic anisotropy possibly infers the development of crystallographic preferred orientation (CPO), and thus it is important to investigate the relationship between deformation and CPO development in constituent minerals of LLSVPs. However, few studies have discussed the relationship from experimental approaches due to the difficulty of deformation experiments under lower mantle pressure conditions. Investigating the relationship between mineral deformation and CPO development in these regions can provide valuable insights.
In this study, we performed large strain deformation experiments on the major lower mantle minerals, (Mg, Fe)O and (Mg, Fe)SiO₃ polycrystals under lower mantle pressure conditions. The aim of this study is to clarify the relationship between the dominant slip system associated with the deformation of LLSVPs and its seismic anisotropy.
We performed torsional deformation experiments on (Mg, Fe)O and (Mg, Fe)SiO₃ polycrystals using rotational diamond anvil cells (rDAC). Pt markers for pre- and post-experimental strain measurements were placed in the sample parallel to the sample rotation axis by focused ion beam (FIB) deposition. All deformation experiments were conducted at BL47XU, SPring-8. Strain of deformed samples were determined from the reconstructed cross-sectional images of Pt markers obtained using X-ray laminography imaging techniques. The strain of the samples were determined from the reconstructed cross-sectional images obtained from the X-ray laminography method, and CPO determination during deformation experiments were attempted from single angle (60 degrees direction to the axis of rotation) XRD. We used Rietveld analysis with a crystal orientation distribution function (ODF) incorporated by MAUD to determine the CPO.
We have deformed (Mg, Fe)O and (Mg, Fe)SiO₃ at pressures of 10-126 GPa, temperatures of 300-950 K, and constant strain rates. For (Mg, Fe)O in the lower mantle pressure range, the dominant slip plane during shear deformation was {100}, consistent with previous studies on MgO. No influence of the iron spin transition on the slip system was observed. Additionally, deformation experiments up to ~60 GPa showed that (Mg, Fe)SiO₃ predominantly deformed along the (010) slip plane.