ELASTICITY AND STRENGTH OF HYDROUS RINGWOODITE AT HIGH PRESSURE

Abstract

OH--bearing (hydrous) ringwoodite compressed non-hydrostatically in a diamond anvil cell supports a differential stress that increases from 2.9 to 4.5 GPa over the pressure range of 6.7-13.2 GPa at room temperature. This result suggests a significant water weakening effect when compared with results from similar experiments on the anhydrous counterpart [Kaver and Duffy, Geophys. Res. Lett. 28 (2001) 2691-2694]. The elastic anisotropy (=2C44/(C11-C12) of hydrous ringwoodite is measured to be 0.87(7) throughout this pressure range, similar to measured values for anhydrous ringwoodite [Kaver and Duffy, Geophys. Res. Lett. 28 (2001) 2691-2694]. This lattice anisotropy cannot be explained by anelastic effects such as faulting and twinning within the structure. These results suggest that hydrous minerals in the upper mantle and transition zone may have higher ductile strain rates for a fixed shear stress at high temperature, resulting in stronger preferred lattice orientation. This, in turn, may be seismically detectable, which opens the possibility of using seismic anisotropy as a marker for local volatile-containing areas within the upper mantle and transition zone.