[S-MP24] Deformed rocks, Metamorphic rocks and Tectonics

[SMP24-P05] Anisotropy of olivine grain boundary slide

*Saya Yoshimatsu ¹, Takehiko Hiraga² (1.The University of Tokyo, 2.Earthquake Research Institute, The University of Tokyo )

The seismic anisotropy observed in the upper mantle is mainly due to the crystallographic preferred orientation (CPO) of olivine, which is dominant mineral in there. The most common type of olivine CPO under mantle convection is A-type, whose [100] and [010] axes are oriented in shear and compression, respectively. Miyazaki et al. (2013) experimentally demonstrated olivine CPO development in the diffusion creep regime, suggesting that crystallographically controlled grain boundary slip may be important. In this study, we experimentally verify this hypothesis, and investigate the contribution of grain boundary slip to A-type development.
Polycrystalline samples containing 90 vol% olivine (forsterite) and 10 vol% clinopyroxene (diopside) are synthesized according to Koizumi et al. (2010). The polycrystalline samples are subjected to a simple shear test to develop A-type according to Kim et al. (2022). From the A-type samples cuboids are cut out so that the angle between vertical plane of them and olivine (010) plane is 45 degrees. The cuboids are compressed uniaxially, and their surfaces were observed with the Atomic Force Microscope (AFM). As a result, the surfaces of each grain are uneven and tilted, indicating grain rotation induced by grain boundary slip during deformation. This result indicates that grain rotation can be analyzed separately in the direction of grain boundary slip.