Plastic deformation of deep mantle minerals will be investigated through high pressure, high temperature deformation experiments to provide a mineral physics background for understanding the style of mantle convection. We shall extend our previous studies that used indirect approach such as the search for systematics in analogue materials or measuring dislocation recovery rates to obtain more direct results on the possible rheological stratification of the deep mantle (the transition zone and lower mantle). The research project has three major components: 
 

• We shall determine the relative strength of high pressure silicate minerals (such as majorite, spinel and perovskite) under high pressures and temperatures.
• We shall investigate the role of grain-size reduction on the rheology of subducting slabs through calculation of grain-size reduction for a variety of slab temperatures combined with a new date set of grain-size sensitive creep and grain growth kinetics in spinel.
• Rheological properties of the lower mantle which is composed of two minerals with a large rheological contrast (a hard perovskite and a soft magnesiowusite) will be investigated through large strain simple shear deformation experiments on analogue materials as well as silicate perovskite plus magnesiowustite mixture.

 

The present research project will provide us with a firm basis for modelling mantle convection and for interpreting seismic tomography in terms of mineral physics.