[S-CG49] Rheology, fracture and friction in Earth and planetary sciences

[SCG49-15] Deformation-enhanced dehydration reaction of serpentinite and its implication to inermediate-depth earthquakes

*Ichiko Shimizu¹, Sakurako Okude¹, Mugen Ogata¹, Katsuyoshi Michibayashi² (1.Division of Earth and Planetary Sciences, Kyoto University, 2.Department of Earth and Planetary Sciences, Nagoya University)

Keywords:Serpentinite, intermediate-depth earthquakes, high-PT deformation experiment, dehydration reaction

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.