日本地球惑星科学連合2022年大会

講演情報

[J] 口頭発表

セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP27] 変形岩・変成岩とテクトニクス

2022年5月27日(金) 15:30 〜 17:00 102 (幕張メッセ国際会議場)

コンビーナ:中村 佳博(国立研究開発法人産業技術総合研究所 地質調査総合センター)、コンビーナ:針金 由美子(産業技術総合研究所)、座長:谷部 功将(東京大学地震研究所)、針金 由美子(産業技術総合研究所)

16:15 〜 16:30

[SMP27-16] Olivine morphology and fabric during diffusion creep: Pure shear experiments

*NAHYEON KIM1AKIHIRO ANDO1Kosuke Yabe1Takehiko Hiraga1 (1.Earthquake Research Institute, University of Tokyo)


キーワード:olivine texture, diffusion creep , grain morphology

We deformed aggregates of Fe-free olivine + 20 vol% diopside in pure shear to study olivine grain morphology and fabric during diffusion creep. Samples were deformed to nearly uniform strains of ~0.7 at different temperatures and experimental durations, which resulted in different grain sizes among the samples due to grain growth. The sample microstructures were observed from each of the three principal stress directions, which revealed various 3D grain morphologies among the samples. Samples with tabular grains displayed a crystallographic preferred orientation (CPO) in olivine, while samples with weakly anisotropic grains had random CPOs. The CPO patterns vary from AG-type (i.e., a uniaxial [010] concentration in the direction of sample shortening) to A-type (i.e., [010] and [100] concentrations in the directions of sample shortening and stretching, respectively), with intermediate types being the most common. The transition from AG- to A-type fabrics is accompanied by a change from oblate to prolate grain morphologies. We explain the direct correlation between the olivine morphology and fabrics based on an inter-granular slip process, which involves preferential grain-boundary sliding at boundaries with fewer steps (ledges). Oblate morphologies with well-developed grain boundaries oriented parallel to (010) indicate slip in the <h0l>{010} system, while relatively prolate morphologies with boundaries parallel to (010) that are elongated along [100] indicates the <100>{010} slip system. Boundaries form parallel to a particular crystallographic plane through anisotropic grain growth that depends on their crystallographic orientation. We propose such grain growth to be the cause of fabric transitions during diffusion creep.