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

通过橄榄石晶体的晶格应变定量估计每个普通球粒陨石所经历的冲击压力

基本信息

批准号：
16540440
负责人：
NAKAMUTA Yoshihiro
金额：
$ 2.24万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

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

我们确定了橄榄石晶体的表观应变之间的相关线，通过X射线粉末衍射方法和冲击压力加载到他们的目的是定量估计的冲击程度所经历的每一个陨石。晶体的微观结构，从其中获得的X射线方法产生的明显的应变，也被推断。用电子探针分析了橄榄石晶体的化学成分后，从抛光薄片上取下约100 μm的小晶体，测定了橄榄石晶体的表观应变。用X射线法测定了橄榄石晶体的表观应变，用透射电镜观察了橄榄石晶体经FIB法处理后的显微结构，并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增加。表示表观应变和冲击压力之间关系的直线的斜率 ...更多信息也随每次实验峰值冲击压力持续时间的增加而逐渐增加，并在2 μs内趋于一个恒定值。根据测定的陨石橄榄石晶体表观应变和估算的陨石各冲击阶段的冲击压力范围，适用于陨石的相关线也限于这样的范围，即可以从橄榄石晶体的表观应变中估计出20%的不确定性的冲击压力。用1.8μs激波实验确定的相关线位于用上述方法得到的相关线的可能区域的中间。然后，通过测量陨石中橄榄石晶体的表观应变，在20%的不确定度下定量估算陨石所经受的冲击压力，并在TEM暗视场图像上测量橄榄石晶体的位错密度。位错密度的对数随表观应变的增加而增加。结果表明，视应变是由冲击形成的位错引起的。少