Mechanisms of target-rock deformation during peak-ring formation

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Crater floors of large terrestrial impact structures, also known as impact basins, are largely flat and dissected by two or more morphological rings. The formation of the innermost ring, the so-called peak ring, and causes of target rock weakening leading to flat crater floors are still unknown. Unravelling these mechanisms are the prime structural geological objectives of Expedition 364 Drilling the K-Pg Impact Crater and this proposal using the Chicxulub impact structure, Mexico, as a terrestrial analogue for the formation of planetary impact basins. Specifically, drill core will be analysed in terms of (1) impact-induced deformation mechanisms, (2) kinematics of deformation, (3) weakening of target rock during cratering and (4) structural evidence of long-term relaxation of crust underlying the crater floor. This will be accomplished by microfabric analysis applying quantitative image analysis using an in-house work flow, electron microprobe analysis, televiewer data and high-resolution 3D volumetric imaging by means of X-ray-computed microtomography. The structural data will be compared to equivalent data from the Sudbury impact structure, Canada, to relate the 1D structural information gained from Expedition 364 drill core to a more comprehensive structural framework of large impact cratering on terrestrial planets.