MD simulations using direct deformation method to apply to diffusion type plasticity have been carried out by means of parallel computing with earth simulator. The direct deformation simulation of MgO can be conducted by anisotropic stress conditions on single crystal induced Shottkey vacancies. The deformation can be measured by anisotropic mean migration distances of vacancies. The results can be obtained as follows: the anisotropic diffusion was possibly simulated by this method by applying the differential stress, and secondly the negative activation volume and negative activation enthalpy for anisotropic diffusion were obtained, and thirdly the diffusion creep resulted from anisotropic diffusion is proportional to the differential stress. These results are consistent with those obtained previously by indirect method.
The dominant deformation mechanism during the Sambagawa metamorphism changes from brittle to ductile with increasing metamorphic temperature. The magnitude of plastic strains inferred from the shapes of deformed radiolaria in metachert increases sharply across the boundary between the epidote‐pumpellyite‐actinolite zone and the epidote‐actinolite zone. The synmetamorphic crack density of metachert is an indicator of the contemporaneous brittle strain of rocks, and it decreases sharply as the grade reaches the epidote‐actinolite zone. Hence, the ratio of the ductile strain to the brittle strain of metachert decreases rapidly across the transition to the epidote‐actinolite zone of the Sambagawa metamorphic belt. The sharp change of the ductile strain magnitude also takes place at the epidote‐actinolite grade in the Shimanto metamorphic belt of Japan, an example of the intermediate pressure facies series of metamorphism. It is concluded that the transition from brittle to ductile deformation takes place at about 300‐400°C. and is independent of pressure of metamorphism.
Mechanical and microstructural evidence indicates that a natural and a synthetic quartzite deformed by Newtonian dislocation (Harper-Dorn) creep at temperatures higher than 1073 K and stresses lower than 300 megapascals. The observation of this creep in these materials suggests that the lower crust may flow like a Newtonian viscous fluid by a dislocation mechanism at stresses much smaller than those previously postulated.
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