Recent Development of Experimental Studies of Plastic Deformation at High-Pressure and Temperature: Some Geophysical Applications

Slow deformation of rocks inside the Earth and other planets controls the way in which Earth loses its heat. The resultant large-scale motion of rocks is responsible for most of geological activities including mountain building, earthquakes and volcanism. Such slow deformation occurs throughout the solid interior of Earth down to ~3000 km from the surface. Pressure and temperature conditions in these areas are extreme (P to ~135 GPa, T to ~4000 K) and the resistance for plastic deformation could change by several orders of magnitude under these conditions. However, experimental studies on plastic deformation under these conditions are challenging, and until recently very little was known on the plastic properties of rocks under the deep Earth conditions. During the last ~10-15 years, a major progress has been made to develop new techniques for studying plastic deformation under high-pressure and temperature conditions using synchrotron X-ray facility combined with a newly developed equipment.  In this presentation, I will provide a historical review of progress in this area and show some of the recent findings including (i) the large pressure effects on plastic deformation, (ii) large contrast in the creep strength of two co-existing minerals in the deep interior of Earth, (iii) the role of grain-size reduction during a phase and (iv) the pressure-induced change in the slip system in MgO.