10:15 AM - 10:30 AM
[SCG52-06] Faulting in deforming dunite under wet conditions: role of aqueous fluid in semi-brittle behavior of dunite
Keywords:dunite, water, deformation, faulting
To revisit the origin of intraslab earthquakes in wet slabs, we conducted uniaxial deformation experiments on as-is dunite and water-saturated dunite at pressures 1-2 GPa and temperatures 670-1250 K with a constant displacement rate using a deformation-DIA apparatus. Pressure, stress, and strain were measured in situ by using x-ray diffraction patterns and radiographies. Acoustic emissions (AEs) were also recorded continuously on six sensors, and three-dimensional AE source location were determined. Formation of throughgoing faults was observed when differential stress exceeds the confining pressure (i.e., Goetze’s criterion) in as-is and water-saturated dunites. Creep strength required for the initiation of a faulting in as-is dunite was quite similar to that in dry dunite (Ohuchi et al., 2017) at each temperature, suggesting that the fracture strength of dunite is not a function of dissolved water content in olivine. Creep strength of water-saturated dunite was systematically lower than that of as-is dunite (~0.5 GPa at each temperature), resulting in decrease in the threshold temperature for a faulting (as-is dunite: 1150 K: water-saturated dunite: ~900 K). Even though the critical strain rate for initiation of a faulting was > 1E-4 /s in as-is dunite, faulting was observed in water-saturated dunite which was deforming at a lower strain rate (between 1E-5 and 1E-4 /s). Increase in AE rate and strong AEs were recorded around the timing of a faulting in both as-is and water-saturated dunites. Increase in strain rate just before a faulting was observed in as-is dunite, not in water-saturated dunite. Strain localization (and thus adiabatic instability) would not be required for the initiation of a faulting in water-saturated dunite.