講演情報
[PPS12-P08]Measurement of Shock Metamorphism of Laser-Shocked Silicates Using X-ray Diffraction
*中村 颯汰1、境家 達弘1、中辻 千陽2、重森 啓介2、西 真之1、近藤 忠1 (1.大阪大学大学院理学研究科宇宙地球科学専攻、2.大阪大学レーザー科学研究所)
キーワード：
石英、衝撃変成、X線回折、ウィリアムソンホールプロット、格子ひずみ
Impact events between planetary bodies are important processes in the early formation of the Solar System and in planetary evolution. Rocks that have undergone such events preserve a variety of shock metamorphic features, and understanding these impact-induced shock effects is indispensable for clarifying impact processes. Traditionally, the classification of shock metamorphic stages has been largely based on optical observations. However, recent studies have attempted quantitative determination of shock stage using X-ray diffraction. This study investigated the shock metamorphism of laser-shocked silicates using a polarizing microscope, a scanning electron microscope (SEM), and a micro-X-ray diffraction analyzer (µXRD). The single-crystal quartz samples, which had been recovered from a shock experiment using a high-power laser, the GEKKO-XII HIPER laser and the GEKKO-Ⅱ laser at Institute of Laser Engineering in The University of Osaka, was observed. Shock metamorphic features such as planar deformation features (PDFs) and feather features (FFs) were observed. To quantify the degree of shock metamorphic features for quartz, X-ray diffraction measurements were performed at different shock pressures on the quartz sample. Cell volumes, the full width at half maximum (FWHM), and the mean maximum lattice strains were obtained using five diffraction peaks: (112), (003), (113), (114), and (223). The cell volume decreased with increasing peak shock pressures estimated with the iSALE shock physics code, and the FWHM showed an increasing trend. The strains were determined from the analysis based on Williamson–Hall plot using the diffraction angle and the integral breadth. A plot of strain versus estimated peak shock pressure shows a linear relationship at peak shock pressures below ~20 GPa: P=(ε+0.002(5))/0.0124(6), where P is estimated peak shock pressure in GPa andεis the strain. Furthermore, when this relationship was applied to single-crystal quartz samples recovered from laser-shock experiments at lower pressures, the calculated peak shock pressures were consistent with the pressures estimated from the laser energy. This result suggests that the shock stage can potentially be quantitatively evaluated from quartz grains in meteorites and impact craters.