[SCG50-P04] Faulting in deforming harzburgite under wet conditions
Keywords:harzburgite, water, semi-brittle flow
To evaluate the effect of water on semi-brittle behavior of harzburgite, we conducted in-situ uniaxial deformation experiments on as-is/water-saturated harzburgite at pressures 1.2-3.0 GPa and temperatures 770-1250 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 radiographs. Acoustic emissions (AEs) were also recorded continuously on six sensors, and three-dimensional AE source location were determined.
Formation of throughgoing faults was observed even when differential stress is much lower than the confining pressure (i.e., > 0.3 times of confining pressure) in water-saturated harzburgite. This is contrast to the case of water-saturated dunite (Ohuchi et al., 2018), in which fracture strength exceeds the confining pressure (i.e., Goetze’s criterion). Creep strength of water-saturated harzburgite was lower than that of as-is harzburgite (~0.5-1 GPa at each temperature). Weakening of the harzburgite by the aqueous fluid resulted in the reduction in the number of AE events and decrease in fault slip rate (< 3.6E-4 s-1 at a stress of < 1.05 GPa). Stress/pressure drop around the timing of a faulting was limited at strains of 1E-4 s-1. The aseismic faulting observed in the water-saturated harzburgite implies that silent slip events around the subduction interface is due to semi-brittle flow of water-saturated harzburgite (i.e., a dehydration product of antigorite).