9706332 Stone Stress-relaxation experiments have demonstrated that many crystalline mineral and metal systems exhibit a mechanical (rheological) equation of state, by which it is possible to completely and uniquely specify the dislocation creep kinetics in terms of a single state variable, which is termed the "hardness" parameter. This state variable must be related to one or more aspects of the deformation- induced microstructure. The PIs propose in this research to determine a microstructural basis for the hardness parameter in terms of statistical distributions of large numbers of dislocations and of larger-scale structures, for example, low-angle (subgrain) boundaries generated during transient and steady state creep. The work focuses on single-crystal Fe-Mg silicate olivine with the ultimate goal of enhancing our ability to accurately extrapolate laboratory creep data to geophysical problems. ***
