Quantitative estimation of the shock pressure experienced by each ordinary chondrite through lattice strain of olivine crystals

我们确定了x射线粉末衍射法得到的橄榄石晶体的表观应变与所受冲击压力之间的相关线，目的是定量估计每块陨石所受的冲击程度。晶体的微观结构，由x射线法得到的明显应变，也被推断出来。从100 μm左右的抛光薄片中取出小晶体，用EPMA分析化学成分，确定橄榄石晶体的表观应变。用FIB法处理后，用透射电镜观察了橄榄石晶体的微观结构，并用x射线法测定了晶体的表观应变。在冲击实验的基础上，发现橄榄石晶体的表观应变随冲击压力的增加而成正比地增加。随着每次实验中冲击压力峰值持续时间的增加，More也逐渐增大，并在2 μs的持续时间内趋于一个恒定值。根据陨石中橄榄石晶体的视应变和陨石各冲击阶段的冲击压力估算范围，适用于陨石的相关线也被限制在橄榄石晶体视应变以20%的不确定度估算冲击压力的范围内。持续时间为1.8μs的激波实验得到的相关线位于上述方法得到的相关线可能区域的中间。然后，通过测量陨石中橄榄石晶体的表观应变，可以定量估计每块陨石所经历的冲击压力，其不确定度为20%。利用透射电镜测量了橄榄石晶体的位错密度。位错密度的对数随视应变的增大而成正比增大。结果表明，表观应变是由冲击形成的位错引起的。少

We determined the correlation line between apparent strains of olivine crystals obtained by the X-ray powder diffraction method and shock pressures loaded on them with the aim of quantitatively estimating the degree of shock experienced by each meteorite. The micro-structures of crystals, from which apparent strains obtained by the X-ray method arise, were also inferred. The apparent strains of olivine crystals were determined by using small crystals taken out from polished thin sections, of about 100 μm in size, after the analysis of chemical compositions by EPMA. Micro-structures of olivine crystals, of which apparent strains were determined by the X-ray method, were observed by TEM after processed by the FIB method.On the basis of shock experiments, it was found that the apparent strains of olivine crystals increase in direct proportion with the increase of shock pressures loaded on them. The slope of the line showing the relation between the apparent strains and the shock pressures … More also increases gradually with the increase of the duration at a peak shock-pressure of each experiment and seems to converge at a constant value over the duration of 2 μs.Based on the apparent strains determined for the olivine crystals from meteorites and the ranges of shock pressures estimated for each shock-stage of meteorites, the correlation line applicable to meteorites is also restricted to the range where shock pressures can be estimated with 20 % of uncertainties from the apparent strains of olivine crystals. The correlation line determined by the shock experiments with 1.8μs duration is in the middle of the probable region of the correlation line obtained by the method mentioned above. Then, shock pressures experienced by each meteorite can be quantitatively estimated with 20 % of uncertainties by measuring apparent strains of olivine crystals in meteorites.The dislocation densities of olivine crystals were measured on the dark-field images taken by TEM. The logarithm of the dislocation density was found to increase in direct proportion with the increase of the apparent strain. The result reveals that apparent strain arises from dislocations formed by shock. Less