THE HISTORY OF DEFORMATION DURING PEAK-RING EMPLACEMENT: LINKING OBSERVATIONS WITH MODELS
Here, we show that the recovered target rocks experienced a sequence of discrete deformation events during peak-ring formation; that there was little to no relative rotation between the recovered target rocks; and that faulting occurred on thousands of individual fractures with displacements ranging from mm’s to dm’s and potentially up to the km scale. Furthermore, whilst the recovered basement rocks have experienced no relative rotation, the orientation of shock micro-structures (Feather Features), combined with numerical simulations, indicate that the entire sequence was rotated by ~90 degrees after the passage of the shock wave. Finally, we show that the deformation of the crystalline rocks by the shock wave and large-scale movement during peak-ring formation, has resulted in extraordinary porosities of 8-10%.
These geological observations are invaluable for calibrating numerical models of peak-ring formation. We have determined the incremental strain history of peak ring material within iSALE simulations of the Chicxulub impact. The modelled deformation history is consistent with the observations, allowing us to place quantitative constraints on the magnitudes, directionality, and rates of rotations, pure and simple shears, and volumetric strain, during the stages of peak-ring emplacement.
Our results provide further support for the dynamic collapse model of peak ring formation. Additionally, these results quantitatively describe the kinematics of peak-ring formation, linked to observed deformation styles within Chicxulub peak-ring material. This information provides crucial kinematic constraints on the dynamics of complex crater collapse.