Shock Metamorphism and High-Pressure Phases in Meteorites

Hypervelocity impact events have been recognized as the form of impact craters on the Earth and planetary surfaces when extraterrestrial materials such as meteorites and comets hit the surfaces. In fact, we can also see many craters on the Moon by eye, and many recent images sent from the observations of solar planets and asteroids show various craters. Impacts are demonstrated to occur very often and play critical roles in forming and evolving planets, including their oceans and atmospheres. The residual effects on rocks and minerals by impact are called shock metamorphism. Some falling meteorites on Earth display shock metamorphism characteristics. Such meteorites have been known to visit the Earth from the Asteroid belt, Mars, and Moon. As shock metamorphism varies with the impact strength and associated energy level, there are many characteristic changes in shock metamorphism, including deformation and microstructure in minerals, solid-state phase transformation to high-pressure minerals, melting and glass formation, vaporization and condensation, etc. They leave many residual changes we observe in the minerals and rocks, and we need to understand impacts by investigating the residual effects in minerals and rocks by the shock compression process. To constrain and understand the shock metamorphism in minerals and rocks, we require direct comparisons between the observed shock metamorphism and the experimentally observed changes by various man-made shock compressions.