Stress-Strain Evolution During Peak-Ring Formation: A Case Study of the Chicxulub Impact Structure

Deformation is a ubiquitous process that occurs to rocks during impact cratering; thus, quantifying the deformation of those rocks can provide first-order constraints on the process of impact cratering. Until now, specific quantification of the conditions of stress and strain within models of impact cratering has not been compared to structural observations. This paper describes a methodology to analyze stress and strain within numerical impact models. This method is then used to predict deformation and its cause during peak-ring formation: a complex process that is not fully understood, requiring remarkable transient weakening and causing a significant redistribution of crustal rocks. The presented results are timely due to the recent Joint International Ocean Discovery Program and International Continental Scientific Drilling Program drilling of the peak ring within the Chicxulub crater, permitting direct comparison between the deformation history within numerical models and the structural history of rocks from a peak ring. The modeled results are remarkably consistent with observed deformation within the Chicxulub peak ring, constraining the following: (1) the orientation of rocks relative to their preimpact orientation; (2) total strain, strain rates, and the type of shear during each stage of cratering; and (3) the orientation and magnitude of principal stresses during each stage of cratering. The methodology and analysis used to generate these predictions is general and, therefore, allows numerical impact models to be constrained by structural observations of impact craters and for those models to produce quantitative predictions. Plain Language Summary During impact cratering events, extreme forces act on rocks beneath the crater to produce deformation. Computer simulations of large impact cratering events are particularly important because the conditions of those events can never be simultaneously produced by laboratory experiments. In this study, we describe a method by which the forces and deformations that occur during cratering can be measured in computer simulations of impact cratering events. Combining this analysis with geological observations from impact structures allows us to improve our understanding of impact crater formation. Here, we use this method to study the Chicxulub impact structure, Mexico, to understand the formation of peak rings, rings of hills found internal to the rim of large impact craters. Our analysis provides estimates of the sequence of forces and deformation during peak-ring formation. As deformation produces fractures, our analysis has important implications for how fluids flow through rocks in craters.