[S-CG49] 地球惑星科学におけるレオロジーと破壊・摩擦の物理

[SCG49-15] 蛇紋岩の変形促進脱水反応と稍深発地震

*清水 以知子¹、奥出 桜子¹、緒方 夢顕¹、道林 克禎² (1.京都大学大学院理学研究科地球惑星科学専攻、2.名古屋大学大学院環境学研究科地球環境科学専攻)

キーワード：蛇紋岩、中深発地震、高温高圧変形実験、脱水反応

Dehydration embrittlement of serpentinite (Raleigh & Paterson, 1965) has been discussed as a possible cause of the intra-slab earthquake but whether or not the same mechanism can be effective at the mantle depths has long been debated. Herein we report the results of deformation and dehydration experiments of antigorite serpentinite conducted at 700 oC temperature and confining pressure up to 1.7 GPa using a modified Kumazawa-type solid-medium apparatus. Samples of antigorite serpentinite collected from the Nagasaki Metamorphic Belt in Japan were used for the experiments. Among four experimental runs using intact core samples of serpentinite, three displayed "dehydration softening" and stable creep behaviors and semi-brittle deformation, whereas one sample did not yield. In the recovered samples, forsterite and hematite were formed along the fault zones, suggesting enhancement of dehydration reaction by fracturing and shear deformation. These observations suggest that deformation of serpentinized slab mantle is affected by initial heterogeneity in serpentinite, and that once brittle failure occurred, dehydration reaction is drastically enhanced and induce further deformation of serpentinite. Deformation and reaction of serpentinite bodies would lead to high pore pressures in surrounding mantle peridotite to induce intraslab earthquakes.