Deformation of periclase single crystals at high pressure and temperature: Quantification of the effect of pressure on slip-system activities

In order to investigate the effect of pressure on periclase (MgO) dislocation slip-system activities, creep experiments have been carried out on MgO single crystals, at T and P, respectively, ranging from 1000 °C to 1200 °C and 4 to 9 GPa, in a deformation-DIA apparatus coupled with x-ray synchrotron radiation. Crystals were deformed in compression along either [100], [100], or [111] directions. These orientations were chosen to activate, respectively, either 1/2〈1-10〉{110} dislocation slip systems, 1/2〈1-10〉{100} systems, or simultaneously 1/2〈1-10〉{110} and 1/2〈1-10〉{100} systems. Experiments are carried out in a temperature range of 1000 °C to –1200 °C and a pressure range up to 8 GPa. Experimental results indicate that pressure influences differently the activities of these slip systems, which should yield a transition of dominant slip systems from 1/2〈1-10〉{110} at low pressure to 1/2〈1-10〉{100}. This pressure induced transition is expected to occur at 23 GPa, which would correspond to a pressure in the top portion of the lower mantle.