Strain localization bands in fine-grained aggregates of germanate olivine and pyroxene deformed by a Griggs type apparatus

Strain localization bands are often observed in natural and experimentally deformed porous rocks in stress state of the transitional regime, from brittle faulting to cataclastic (or ductile) flow. The rock samples used in most of the previous studies were natural porous coarse sandstones. Meanwhile, fine-grained aggregates originating from powders were used as an initial sample for high-pressure coaxial deformation experiments. Generally, compaction for sintering these aggregates were performed before the experiments. No coaxial experiments have been performed the compaction of the powder under high pressure and low temperature during experiments (cold pressing). This stress state during sintering is close to the transitional regime from brittle faulting to cataclastic flow, hence, there is a possibility that compaction bands which are a type of strain localization bands may form at the cold-pressing stage of deformation in laboratory experiments. We conducted cold pressing experiments on the powder of fine-grained germanate olivine and pyroxene with approximately 30% porosity using a Griggs type apparatus. The experiments reveal that compaction bands form in the compacted and sintered sample. Microstructural analysis revealed that grains with a high dislocation density rotate and crush with shear strain concentration during compaction. At the end of the compaction, the grain size becomes small and bands are made of fine-grained material.