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

为了了解压力对地幔成分矿物塑性的影响，在49次实验的基础上，提出了一种利用多砧高压仪器和x射线照相系统进行变形实验的新方法。在本实验中，同步辐射产生的强x射线束穿过多砧装置的砧隙，在高达7 Gpa的高压和高温条件下照射样品，到达CCD摄像系统。这个压力范围几乎是普通变形仪产生的压力范围的三倍。利用该技术，可以在8μm左右的精度范围内实时观察样品图像并测量样品长度的变化。通过导块和砧的行程变化，可以估算出试样所受的应力值。该实验技术已应用于圆柱形烧结橄榄石的变形实验。实验条件为5 ~ 7 Gpa压力，900 ~ 1300℃，2.5×10^<-6>/s应变速率（约0.2 Gpa应力）。回收试样的力学数据和显微组织观察表明，试样是位错滑动变形。然而，以往在低于1 Gpa压力下对橄榄石进行的变形实验表明，在与本研究相同的温度和应变速率条件下，位错蠕变是活跃机制。这种差异表明压力对其有影响。也就是说，在橄榄石的变形机制图中，幂律蠕变的优势区即位错蠕变，随着压力的增加，在低剪应力方向上减小。

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.