The PI's experimental studies during the previous funding periods have demonstrated that the deformation fabrics (lattice preferred orientation: LPO) in olivine under high water content conditions are markedly different from those under water-poor conditions. Some of the fabrics in naturally deformed peridotites and some of the observed seismic anisotropy in the upper mantle may reflect these water-induced fabric transitions in olivine. However, previous research has major limitations in that the scaling laws for fabric transitions have not been quantified and the roles of other minerals such as orthopyroxene have not been explored. In this new proposal, the investigator proposes to extend the previous studies in the following directions. First, they will determine the scaling laws of fabric diagram with a focus on the effects of temperature. Second, they will investigate microscopic mechanisms controlling the varieties of microstructures with the emphasis on deformation mechanism boundary. Their preliminary results suggest that water may enhance diffusion-related processes more than dislocation-controlled processes. The large-strain shear deformation technique developed in the investigator's lab together with a newly installed high-resolution SEM (scanning electron microscope) will be utilized in this study. The results will have important implications for interpreting deformation fabrics of naturally deformed rocks as well as for the interpretation of seismic anisotropy. The research described in this proposal will comprise a major component of Phil Skemer's Ph D thesis.
