Imaging and Drilling the Chicxulub Impact Crater: Testing Models for Crater Collapse

Seismic data acquired in 1996 and 2005 image the buried and surprisingly asymmetric final crater of the 65 Ma Chicxulub impact crater, and highlight features targeted in proposed IODP-ICDP drilling. Strong international interest exists in drilling the intact peak ring to calibrate models of peak ring formation in large impacts. Peak rings are present in nearly all known large impacts on rocky planetary bodies in the solar system. Gravitational collapse of the transient crater at Chicxulub created a terrace zone consisting of faulted slump blocks that reach the greatest depth in the northwest. The topographic peak ring overlies the innermost slump blocks of the terrace zone in all imaged azimuths suggesting interaction of the inward slumping terrace zone and the rebounding central uplift is important for the formation of the peak ring as suggested in modeling. Asymmetry in the peak ring allows for sampling the lithologies beneath the topographic peak ring at relatively shallow depths in order to explain how the proposed deep crustal material can result in lower velocities and densities than the surrounding rocks. Dipping seismic reflections are present beneath the peak ring that may represent a lithologic base of the peak ring material, or a marker for an extinct hydrothermal system; mismatch in the location of the peak ring low velocity zone versus the dipping reflections favor a non-lithologic origin. Bright, discontinuous reflections toward the interior may represent the top of the impact melt sheet overlain by re-surge deposits and capping the central uplift. A proposed drilling transect plans to penetrate and sample: 1) the earliest Tertiary sediments and underlying dipping reflectivity, 2) shallow to medium lithologies of the peak ring, and 3) the intact melt sheet. These sites should calibrate models of peak ring formation and crater collapse and investigate destruction and creation of habitat.