[S-CG46] Rheology, fracture and friction in Earth and planetary sciences

[SCG46-07] Dehydration experiments of antigorite serpentinite under slab-mantle conditions

Sakurako Okude¹, *Ichiko Shimizu¹ (1.Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University)

Keywords:serpentinite, dehydration reaction, deformation experiments, intermediate-depth earthquakes

A popular hypothesis for the occurrence of double seismic zones in subducting slabs is "dehydration embrittlement" of serpentinized mantle. In the classical deformation experiments of antigorite-serpentinites conducted by Raleigh & Paterson (1965), brittle failure was observed at the temperature beyound the stability field of antigorite (> 650 ^oC) at the confining pressures up to 0.5 GPa. However, it is questionable if the same mechanism could be effective in subducting slabs at the depth. Here we report the results of deformation and dehydration experiments of antigorite-serpentinite, taken from the Nagasaki Metamorphic Belt, at comfining pressures up to 1.7 GPa. Using a modified Kumazawa-type solid-medium apparatus, intact serpentinite samples were axially compressed at a constant strain rate of 3.3 x 10^-5 sec^-1, while laterally confined by talc assembly.

In the experimental run at 500 ^oC and 1.2 GPa confining pressure, the serpentinite wample was strong and show strain-hardening behavior. The final differential stress exceeded 1.8 GPa. The sample was deformed in a brittle mannar with conjugate faults. The samples deformed at 700 ^oC exhibited "dehydration softening" and stable creep behaviors and showed semi-brittle deformation. Forsterite and enstatite were formed along the fault zones, suggesting enhancement of dehydration reaction by fracturing and shearing. Implication of the present results to the mechanism of intermediate-depth earthquakes well be discussed.