Characterization of Artificially Shocked forsterites: (1) Diffraction Profile Analysis by Gandolfi Camera

摘要

We have examined synthetic single crystals of forsterites shocked up to 82GPa using a single stage propellant gun. Even in forsterites shocked to 82GPa, any decomposition phases such as spinels or silica glasses and fine-grained MgO could not be detected by X-ray diffraction and EPMA methods. Profile analysis of X-ray diffraction peaks of the shocked forsterites using a Gandolfi camera has been done to detect the maximum strain. The maximum strain derived from Williamson-Hall plot of about 20 diffraction angles and their integral maximum breadths had a linear relation to the shock pressures, in which the elastic limit could not be detected. Unit cell dimensions did not show any changes against the shock pressures, however the increasing broadening of X-ray diffraction peaks occurred with the increase of shock pressures, indicating the homogeneous lattice distortion due to shock pressures. This is the first quantitative analysis that enables us to estimate an experienced shock pressure from the X-ray peak broadening, and is applied to the Dhurmsala LL6 chondrite; the pressure estimated in this study is ranging from 24.0 to 37.8GPa in contrast to the range of 5 to 20 GPa (shock stage S3 by Stoeffler et al, 1991) estimated from the texture of olivine in the chondrite.