Deformation Experiment of Antigorite Serpentinite with a Solid Medium Deformation Apparatus

Serpentinite is believed to be widespread in and along oceanic plates undergoing subduction. Deformation of serpentinite probably plays an important role in subduction and exhumation process of slab. However, rheological behavior of serpentinite is poorly understood, especially at more than 1GPa. We conducted constant strain rate experiments of antigorite serpentinite to understand the rheological behavior of it using modified Griggs type apparatuses. Experimental conditions were 1 GPa and 3GPa confining pressures, 300 C to 700 C, and 2.0 to 2.4E-5/s of strain rate. The serpentinite sample was collected from Nagasaki metamorphic rock in Japan. The sample was cored parallel to the foliation plane for the starting materials. The sizes of starting materials were ca. 7.0 mm diameter "~ ca. 7.0 mm length or ca. 3.0 mm diameter "~ ca. 8.0 mm length. The mechanical data indicate the following two characteristics: 1) the flow stress at same temperature increases with an increasing confining pressure, 2) temperature dependence flow stress also increases with an increasing confining pressure. The second character is probably attributed to change of deformation mechanism. We are now observing the microstructures of recovered samples with TEM to clarify the deformation mechanism. In the sample from 3GPa and 600 C conditions, many stacking faults developed compared with the starting sample, which suggests that formation process of stacking faults controls the plastic deformation of antigorite at high pressure.