New experiments on the mechanical properties of minerals at high pressures: Implications for the strength of the Earth's mantle and the mechanism of deep-focus earthquakes

First, we document techniques for measuring the static strength of minerals to pressures as high as 80 gigapascals (GPa) in the diamond anvil cell. These are the first creep experiments ever carried out above 10 GPa. In several instances, we find that the pressure dependence of the strength at room temperature is higher than the value predicted by the elastic continuum theory of dislocations. We also find that the strength of minerals often decreases across phase transformations that involve an increase in coordination and nearest neighbor distance. Experiments on silicates at high pressures show that (Mg,Fe);We describe observations of acoustic emissions and shear instabilities associated with the ;We also describe new techniques for making high precision powder x-ray diffraction measurements at high pressures. We show that by analyzing two-dimensional angle-dispersive powder diffraction patterns, one can measure changes in the scattering angle 2...