Stress and strain during shock metamorphism
Auriol S.P. Rae, Michael H. Poelchau, Thomas Kenkmann
In Press, Journal Pre-proof, Available online 1 September 2021
• We show the orientation and magnitude of stress and strain in shock waves during impact cratering.
• Stress and strain rotation during natural shock events is a fundamental geometrical consequence of the interaction of the shock and rarefaction waves.
• Structural interpretations of impact craters using simplified assumptions of a radial orientation of shock metamorphic effects can now be improved.
• Understanding stress and strain orientation during shock can constrain the mechanism and timing of specific shock deformation effects, such as shatter cones.”
“Shock metamorphism is the process by which rocks, and the minerals within them, transform during the passage of a shock wave. Shock effects, such as shatter cones, are critical for the identification of impact structures and have commonly been used to infer mechanical and structural information on the cratering process. To make these inferences, the mechanics of shock wave behavior must be understood. Here, we use numerical simulations to demonstrate how stresses act during shock metamorphism across all regions of the target that experience solid-state shock metamorphism. Furthermore, our numerical simulations predict the strains that are produced as a consequence of those stresses. The results show that the magnitude and orientation of stress and strain during shock metamorphism are variable throughout the target, both spatially and temporally, even between rocks that experience the same peak shock pressure. The provenance of a sample relative to the point of impact and the timing/mechanism of the formation of a shock effect must both be considered when making structural interpretations. The stress and strain magnitudes and orientations as functions of time and location presented in this study provide the constraints that enable a greater understanding of the formation of a variety of shock deformation effects. We demonstrate this with a case study of shatter cones at the Gosses Bluff impact structure. Our results provide a useful guide to assist geologists and petrologists in the interpretation of shock metamorphic effects.”