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

点击翻译按钮获取中文摘要

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