LABORATORY IMPACT EXPERIMENTS VERSUS NATURAL IMPACT EVENTS

Abstract

Laboratory studies of shock metamorphism have long provided a basis for recognition of the diagnostic features of ancient terrestrial impact craters. However, there are significant differences between the range of parameters accessible in laboratory impact experiments and the conditions of large natural impact events. The basic premise of the laboratory calibrations is that peak pressure is the most significant parameter governing shock metamorphism. To show that other parameters are important, the shock formation of diamond is discussed in detail. Shock-induced phase transitions in silicates are discussed in the framework of current efforts to infer possible kinetic effects. In an effort to encourage critical examination of the literature, we call attention to the characteristics and limitations of experimental techniques. Particular emphasis is placed on the value of thoroughly documenting both the details of shock-loading experiments and the assumptions underlying shock calculations, to permit eventual reassessment of the results in the light of new information.