2:30 PM - 2:45 PM
[U04-04] Semi-brittle flow in dunite and harzburgite at upper mantle pressures
Keywords:water, semi-brittle flow, faulting
To evaluate the effect of water on semi-brittle behavior of dunite and harzburgite, we conducted in-situ uniaxial deformation experiments on as-is/water-saturated dunite and harzburgite at pressures 1-3 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 radiographs. Radiographs were taken at each several minutes in most of deformation experiments, though radiographs were continuously taken (each 5 seconds) during a deformation run (at 2 GPa and 860 K). Acoustic emissions (AEs) were also recorded continuously on six sensors, and three-dimensional AE source location were determined.
Formation of throughgoing faults was observed in water-saturated dunite and harzburgite at 860 K and lower temperatures. Fault slip rate is between 3E-5 and 4E-4 s-1 which are comparable to the background strain rate just before a faulting (1E-5 and 3E-4 s-1), showing that shear localization is ineffective under water-saturated conditions. Addition of the aqueous fluid resulted in the reduction in the number of AE events in the faulted sample (i.e., aseismic faulting). A high time-resolution strain monitoring revealed that fault slip rate fluctuate within several ten seconds (i.e., stick-slip phenomena). Because the high time-resolution strain monitoring is a preliminary experiment, the relationship between stick-slip phenomena and aqueous fluid is unclear. We will investigate that point in near future.