Crystal plasticity of natural garnet: New microstructural evidence

Scanning electron microscope (SEM) orientation contrast images of mantle no dules show that garnets contain cellular domains of different crystallograp hic orientation. Electron backscatter diffraction shows small crystallograp hic mismatches (<3<degrees>) across cell boundaries. A transmission electro n microscope examination of an area containing these substructures shows th at the cell boundaries comprise arrays of dislocations and are subgrain bou ndaries. The observed garnet substructures relate to high-temperature dislo cation creep and recovery. This is the first time that subgrains have been shown to occur in a significant volume of an individual garnet. Wider appli cation of new SEM techniques may enable us to use garnet microstructures to determine deformation conditions more exactly and will aid interpretation of garnet microchemical data.