[S-CG50] Rheology, fracture and friction in Earth and planetary sciences

[SCG50-P01] Highly dense fine-grained upper mantle composites synthesized from sedimentary mud in the peridotite quarry

*Sanae Koizumi¹, Takehiko Hiraga¹ (1.Earthquake Research Institute,The University of Tokyo)

Keywords:Peridotite, Horoman, sedimentary mud, Wet Pulverization, Spark plasma sintering, Grain size

High-precision deformation experiments of olivine aggregate by Yabe and Hiraga 2020 have revealed that the addition of Ca and Al, which partition (segregate) to grain boundaries, to olivine aggregate can enhance grain boundary diffusion, resulting in weakening of the aggregate. The result indicates that "impurities" in natural rocks control the strength of the upper mantle. Ideally, we can conduct high temperature deformation experiments and analyze mechanical properties using real upper mantle composites to further investigate the impurity effect, while it is experimental challenging due to the sample qualities such as mineral distribution, grain size, porosity and so on. To solve this problem, we attempted to develop a peridotite sample synthesis method for laboratory measurements. We collected sedimentary mud from the peridotite quarry in Horoman, Hokkaido, Japan. Chemical composition of the mud was found to represent the compositions of various types of peridotite exposed in 80 km² of the area. By jet milling mud with grain size smaller than 45 μm in an aqueous solution, a submicron powder was obtained while avoiding contamination. To improve the particle size distribution of the powder, the hydraulic elutriation was used in addition to the pulverization process. We applied pressure-assisted Spark plasma sintering at low temperature and short time. The microstructures of the synthesized sintered compacts were evaluated using scanning electron microscopy and transmission electron microscopy. We successfully synthesized highly dense (porosity <1%) and fine-grained (~1 µm) upper mantle composite without cracks or melts.