4:15 PM - 4:30 PM
[PPS06-04] Hypervelocity impacts on calcite sand: Peak pressure distribution around the impact point
Keywords:Shock metamorphism, Shock recovery, Calcite, Electron microscopy
Hypervelocity impact is a geological process that irreversibly converts kinetic energy of the Keplerian motion around the Sun into thermal energy by generating shock waves [e.g., Ahrens&O'Keefe72, Moon 4, 214-249]. Shock metamorphic textures formed during impacts have been discovered in various meteorites and lunar samples, and have been used to reconstruct the history of the mutual collisions in the solar system in the past [e.g., Marchi+13, Nature Geo. 6, 303-307]. In order to reconstruct the past, it is necessary to accurately understand the momentum and energy transfer during shock wave propagation. The pressure and temperature required for producing metamorphic features have been estimated by assuming that an asteroid is a homogeneous medium. However, natural rocks are mixtures of minerals and they are heterogeneous in density and size, and have grain boundaries and voids. In recent years, the numerical method that can handle multiple materials at mesoscale have been developed, and it has become possible to numerically solve the propagation of shock waves in such complex systems. As a result, it has been recognized that significant spatial heterogeneity in pressure and temperature occurs in complex systems [Bland+14, Nature Comm. 5, 5451]. In order to interpret the results of analyses of shocked samples, such inhomogeneity should also be taken into account. We believe that It is essential to empirically investigate the energy distribution process at the impact point to elucidate the formation and destruction of solar system bodies.
We attempted to recover a shocked powder target without scattering and to measure the pressure distribution within the structure. When the experimental conditions are optimized, a bowl-shaped structure (hereafter referred to as a ‘bowl’) is left at the center of the impact crater, and it is possible to recover a small amount of material from directly below the impact point [Kurosawa+23, JpGU]. Recently, the study by a part of the authors of the present abstract have conducted shock recovery experiments on marble (a conglomerate of calcite), and made a classification table pertaining to quantify the shock pressures in calcite grains (Tomioka+25, American Mineralogist, in press). In this study, we applied this shock-induced classification table to bowls.
We used a vertical two-stage hydrogen gas gun installed at the Institute of Space and Astronautical Science (ISAS) of JAXA. The same marble used in the previous study was crushed and processed into calcite sand. Aluminium sphereas with a diameter of 2 mm were shoot into the calcite sand vertically at ~3 km/s. The pressure at the point of impact, calculated from the shock Hugoniot oarameters of aluminium and calcite crystals, was about 20 GPa. After the experiment, the bowl was recovered, filled by a resin, and then cut and polished into thin sections. The shock metamorphic structure was observed using a polarized microscope, a scanning electron microscope (SEM–EBSD) equipped with a backscattered electron detector placed at The University of Tokyo, and a transmission electron microscope (TEM) installed at JAMSTEC.
The observations revealed that (1) the degree of damage due to plastic deformation of the calcite grains within the bowl depends on the distance from the impact point and (2) when the classification table by Tomioka+25 is applied, the pressure decreases to <4 GPa at a distance of ~1 mm from the impact point.
Acknowledgments: This work was supported by ISAS/JAXA as a collaborative program with the Hypervelocity Impact Facility. This research was supported by JSPS KAKENHI Grant No. JP21K18660.
We attempted to recover a shocked powder target without scattering and to measure the pressure distribution within the structure. When the experimental conditions are optimized, a bowl-shaped structure (hereafter referred to as a ‘bowl’) is left at the center of the impact crater, and it is possible to recover a small amount of material from directly below the impact point [Kurosawa+23, JpGU]. Recently, the study by a part of the authors of the present abstract have conducted shock recovery experiments on marble (a conglomerate of calcite), and made a classification table pertaining to quantify the shock pressures in calcite grains (Tomioka+25, American Mineralogist, in press). In this study, we applied this shock-induced classification table to bowls.
We used a vertical two-stage hydrogen gas gun installed at the Institute of Space and Astronautical Science (ISAS) of JAXA. The same marble used in the previous study was crushed and processed into calcite sand. Aluminium sphereas with a diameter of 2 mm were shoot into the calcite sand vertically at ~3 km/s. The pressure at the point of impact, calculated from the shock Hugoniot oarameters of aluminium and calcite crystals, was about 20 GPa. After the experiment, the bowl was recovered, filled by a resin, and then cut and polished into thin sections. The shock metamorphic structure was observed using a polarized microscope, a scanning electron microscope (SEM–EBSD) equipped with a backscattered electron detector placed at The University of Tokyo, and a transmission electron microscope (TEM) installed at JAMSTEC.
The observations revealed that (1) the degree of damage due to plastic deformation of the calcite grains within the bowl depends on the distance from the impact point and (2) when the classification table by Tomioka+25 is applied, the pressure decreases to <4 GPa at a distance of ~1 mm from the impact point.
Acknowledgments: This work was supported by ISAS/JAXA as a collaborative program with the Hypervelocity Impact Facility. This research was supported by JSPS KAKENHI Grant No. JP21K18660.