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

[SCG62-P01] Grain Growth and Diffusion Creep in Materials with Bicontinuous Structure: Experiments and Mechanism Investigation

*Shenghao Jiang¹, Takehiko Hiraga² (1.Department of Earth and Planetary Science, University of Tokyo, 2.Earthquake Research Institute, the University of Tokyo)

Keywords:grian growth, creep, diffusion, bicontinuous structure

Grain growth and plastic deformation are two essential processes within the mantle in which diffusion plays an important role. In mono-phase systems, grain growth only requires atomic diffusion across grain boundaries (short-range diffusion). In multi-phase systems, grain growth requires long-range diffusion from smaller to larger grains of the same phases. Earth materials (rocks) are commonly multi-phase systems. As a first-order approximation, we consider two-phase systems. The phase distribution of a two-phase system varies depending on the volume fraction of the secondary phase. When the volume fraction of the secondary phase is less than ~36%, grains of the secondary phase are isolated from each other, and when the volume fraction is greater than ~36%, both grains of the same phases are interconnected, which we call a bicontinuous structure. Okamoto and Hiraga (2022) showed that creep and grain growth in the isolated case proceed through the same diffusion mechanism. However, this conclusion does not necessarily hold for the bicontinuous case. In this study, we performed grain growth and creep experiments on the forsterite-periclase systems with and without bicontinuous structure. Since the rate-controlling elements for diffusion differ between forsterite and periclase, we can figure out the diffusion path based on the rates of growth and creep. Our results show that creep and grain growth in the bicontinuous case proceed through different diffusion mechanisms.