Determination of flow law of olivine at high P and T conditions using synchrotron radiation, high pressure apparatus,and CCD camera system

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A new technique of deformation experiment using a multi-anvil high pressure apparatus and X-ray radiography system has been developed on the basis of 49 experiments, in order to understand a pressure effect on the plasticity of mantle constituent minerals. With this experiment, strong X-ray beam from synchrotron radiation passes through the anvil gaps of multi-anvil apparatus, and irradiates sample under high pressure, up to 7 Gpa, and temperature conditions, and then reaches CCD camera system. This pressure range is almost three times larger than that generated by ordinary deformation apparatus. By using this technique, we can observe real time image of sample and measure the change of sample length within a precision about 8μm. And we can estimate the stress values applied to sample from stroke change of guide block and anvils.This experimental technique has been applied to the deformation experiment of cylindrical sintered olivine. The experimental conditions were 5 to 7 Gpa pressure, 900℃ to 1300℃, and about 2.5×10^<-6>/s strain rate (about 0.2 Gpa stress). The mechanical data and microstructural observation of retrieved sample suggest that sample was deformed by dislocation glide mechanism. However, the previous deformation experiments of olivine conducted at lower than 1 Gpa pressure demonstrate that the dislocation creep is active mechanism at the same temperature and strain rate conditions as present study. This discrepancy suggests the pressure effect on it. That it to say, the dominant region of power law creep, namely dislocation creep, in the deformation mechanism map of olivine decreases in the direction of lower shear stress with increasing pressure.