4:00 PM - 4:15 PM
[SCG44-03] Grain growth and creep experiments on a solid-state bicontinuous system
Keywords:viscosity, forsterite, diopside, diffusion creep, grain growth, bicontinuous structure
Diffusion creep is an important deformation mechanism in the Earth's interior. Convection in the lower mantle or the whole mantle may proceed via diffusion creep. The strain rate of diffusion creep is very sensitive to the grain size, so changes in grain size affect the earth's rheological properties significantly. In general, grains grow spontaneously to reduce the energy of the system. Therefore, to understand the flow of the earth's interior materials, we must consider creep and grain growth together.
In most cases, rocks are simplified to a mono-phase system of the most abundant minerals and used to yield parameters such as viscosity. However, such simplifications are different from reality. In the case of two-phase systems, the volume fraction is an important parameter. When the volume fraction of one phase is small, the minor phase is isolated and the grain growth mechanism corresponds to the theoretical model of Ostwald ripening subjected to Zener pinning. When the volume fraction of the minor phase exceeds 36%, both phases become continuous, the structure of which is referred to as a bicontinuous structure, and the corresponding grain growth mechanism is unknown in this case. The bicontinuous structure is also very important for studying deformation in two-phase systems. In a bicontinuous structure, both phases are "major phases" and it is difficult to predict the bulk viscosity, especially when the end-member viscosities are very different.
In this study, we investigated grain growth, creep, and their relationship in a two-phase system with a bicontinuous structure using forsterite + 50vol% diopside aggregates. The viscosity of the two end members differs by more than one order of magnitude (forsterite is more viscous) and diffuses in different ways (grain boundary diffusion for forsterite and lattice diffusion for diopside).
The experimental results showed that our samples were deformed by diffusion creep. The bulk viscosity is consistent with the viscosity of a forsterite single-phase aggregates. This suggests that the viscosity of the solid-state two-phase system with a bicontinuous structure is determined by the stronger phase. Comparing the results with the iso-strain rate and iso-stress models, it is found that our experimental results correspond well to the iso-strain rate model but have a higher viscosity. Grain growth experiments also exhibit characteristics similar to those of forsterite-rich samples but at a relatively slower growth rate.
In most cases, rocks are simplified to a mono-phase system of the most abundant minerals and used to yield parameters such as viscosity. However, such simplifications are different from reality. In the case of two-phase systems, the volume fraction is an important parameter. When the volume fraction of one phase is small, the minor phase is isolated and the grain growth mechanism corresponds to the theoretical model of Ostwald ripening subjected to Zener pinning. When the volume fraction of the minor phase exceeds 36%, both phases become continuous, the structure of which is referred to as a bicontinuous structure, and the corresponding grain growth mechanism is unknown in this case. The bicontinuous structure is also very important for studying deformation in two-phase systems. In a bicontinuous structure, both phases are "major phases" and it is difficult to predict the bulk viscosity, especially when the end-member viscosities are very different.
In this study, we investigated grain growth, creep, and their relationship in a two-phase system with a bicontinuous structure using forsterite + 50vol% diopside aggregates. The viscosity of the two end members differs by more than one order of magnitude (forsterite is more viscous) and diffuses in different ways (grain boundary diffusion for forsterite and lattice diffusion for diopside).
The experimental results showed that our samples were deformed by diffusion creep. The bulk viscosity is consistent with the viscosity of a forsterite single-phase aggregates. This suggests that the viscosity of the solid-state two-phase system with a bicontinuous structure is determined by the stronger phase. Comparing the results with the iso-strain rate and iso-stress models, it is found that our experimental results correspond well to the iso-strain rate model but have a higher viscosity. Grain growth experiments also exhibit characteristics similar to those of forsterite-rich samples but at a relatively slower growth rate.