11:00 AM - 1:00 PM
[PPS08-P02] Evaluation of metamorphism of laser-shocked SiO2 using micro-focused X-ray diffraction
Keywords:silica, high-pressure minerals, shock metamorphism, laser shock recovery experiment, micro-focused X-ray diffraction
1. Introduction
The impact event of small bodies is important as one of the elementary processes of planet formation and evolution, and in meteorites, the most common extraterrestrial materials available to us, various shock-metamorphosed minerals have been found. Using high-power laser, we have developed a technique for recovering samples impacted more than 10 km/s, which is difficult to achieve with a conventional gas gun, analyzing the shock metamorphism in the recovery samples [1]. Recently, we have conducted shock recovery experiments with high-power laser to understand the shock metamorphism of SiO2 in natural meteorite, and succeeded in almost entirely recovering powder samples that have undergone laser shock more than about 100 GPa. In this study, we will report the high-pressure metamorphic distribution in the laser-shocked samples investigated by optical microscopy and micro-focused X-ray diffraction measurement.
2. Experiment
The sample analyzed in this study is a recovered synthetic α-quartz powder of several µm in the initial grain size, which was shock-compressed by the GEKKO-XII (HIPER) laser at the Institute of Laser Engineering in Osaka University. The shock pressure at the sample surface is estimated to be about 80-130 GPa. The laser shock experiment was performed using a sample recovery cell, which is similar to the one reported in the past for single crystal samples [1]. The recovered samples were cut near the center, and thin sections (50-70 µm thick) were prepared to observe the depth profile of metamorphism from the impact point. Each thin section was analyzed by optical microscopy in reflected and transmitted light, followed by micro-focused X-ray diffraction measurement (RINT RAPID II, RIGAKU Co. Ltd.) using collimators of φ30 µm and φ100 µm. From the X-ray diffraction profiles (2θ=20°-80°), we identified the high-pressure phase and observed its distribution in shocked area, as well as evaluated remained nonuniform lattice strain and lattice volume in the quartz crystal at each measurement point.
3. Result & Discussion
As a result of optical microscope observation of the cross-section of the shocked sample, it was found that different shock metamorphisms showing apparently white and black color, were almost concentrically distributed and formed a layered structure from impact point. The results of X-ray diffraction measurement showed that stishovite was quenched in the metamorphic white region. Furthermore, diffraction patterns which are not consistent with either the known stable phase of SiO2, titanium or aluminum were observed, suggesting the recovery of unknown phase. For the quartz in the recovered sample, the full width at half maximum of diffraction peaks and the calculated lattice volume increased at near the impact point, and approached the values of the starting sample with depth. In this presentation, we will report the details of distribution of metamorphism in laser-shocked SiO2 based on the results of optical microscopy and X-ray diffraction observations.
Reference
[1] K. Nagaki et al.: Meteoritics & Planetary Science, 51, 1153-1162 (2016)
The impact event of small bodies is important as one of the elementary processes of planet formation and evolution, and in meteorites, the most common extraterrestrial materials available to us, various shock-metamorphosed minerals have been found. Using high-power laser, we have developed a technique for recovering samples impacted more than 10 km/s, which is difficult to achieve with a conventional gas gun, analyzing the shock metamorphism in the recovery samples [1]. Recently, we have conducted shock recovery experiments with high-power laser to understand the shock metamorphism of SiO2 in natural meteorite, and succeeded in almost entirely recovering powder samples that have undergone laser shock more than about 100 GPa. In this study, we will report the high-pressure metamorphic distribution in the laser-shocked samples investigated by optical microscopy and micro-focused X-ray diffraction measurement.
2. Experiment
The sample analyzed in this study is a recovered synthetic α-quartz powder of several µm in the initial grain size, which was shock-compressed by the GEKKO-XII (HIPER) laser at the Institute of Laser Engineering in Osaka University. The shock pressure at the sample surface is estimated to be about 80-130 GPa. The laser shock experiment was performed using a sample recovery cell, which is similar to the one reported in the past for single crystal samples [1]. The recovered samples were cut near the center, and thin sections (50-70 µm thick) were prepared to observe the depth profile of metamorphism from the impact point. Each thin section was analyzed by optical microscopy in reflected and transmitted light, followed by micro-focused X-ray diffraction measurement (RINT RAPID II, RIGAKU Co. Ltd.) using collimators of φ30 µm and φ100 µm. From the X-ray diffraction profiles (2θ=20°-80°), we identified the high-pressure phase and observed its distribution in shocked area, as well as evaluated remained nonuniform lattice strain and lattice volume in the quartz crystal at each measurement point.
3. Result & Discussion
As a result of optical microscope observation of the cross-section of the shocked sample, it was found that different shock metamorphisms showing apparently white and black color, were almost concentrically distributed and formed a layered structure from impact point. The results of X-ray diffraction measurement showed that stishovite was quenched in the metamorphic white region. Furthermore, diffraction patterns which are not consistent with either the known stable phase of SiO2, titanium or aluminum were observed, suggesting the recovery of unknown phase. For the quartz in the recovered sample, the full width at half maximum of diffraction peaks and the calculated lattice volume increased at near the impact point, and approached the values of the starting sample with depth. In this presentation, we will report the details of distribution of metamorphism in laser-shocked SiO2 based on the results of optical microscopy and X-ray diffraction observations.
Reference
[1] K. Nagaki et al.: Meteoritics & Planetary Science, 51, 1153-1162 (2016)