Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition 364

Abstract

Highlights  Chicxulub peak-ring rocks have low velocities and densities, and high porosities.  Physical property values indicate considerable damage of granitoid peak-ring rocks.  Suevite flowed downslope during and after peak-ring formation Abstract. Joint International Ocean Discovery Program and International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub impact crater. We present P-wave velocity, density, and porosity measurements from Hole M0077A that reveal unusual physical properties of the peak-ring rocks. Across the boundary between post-impact sedimentary rock and suevite (impact melt-bearing breccia) we measure a sharp decrease in velocity and density, and an increase in porosity. Velocity, density, and porosity values for the suevite are 2900-3700 m/s, 2.06-2.37 g/cm 3 , and 20-35%, respectively. The thin (25 m) impact melt rock unit below the suevite has velocity measurements of 3650-4350 m/s, density measurements of 2.26-2.37 g/cm 3 , and porosity measurements of 19-22%. We associate the low velocity, low density, and high porosity of suevite and impact melt rock with rapid emplacement, hydrothermal alteration products, and observations of pore space, vugs, and vesicles. The uplifted granitic peak ring materials have values of 4000-4200 m/s, 2.39-2.44 g/cm 3 , and 8-13% for velocity, density, and porosity, respectively; these values differ significantly from typical unaltered granite which has higher velocity and density, and lower porosity. The majority of Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable rock damage, and are consistent with numerical model predictions for peak-ring formation where the lithologies present within the peak ring represent some of the most shocked and damaged rocks in an impact basin. We integrate our results with previous seismic datasets to map the suevite near the borehole. We map suevite below the Paleogene sedimentary rock in the annular trough, on the peak ring, and in the central basin, implying that, post impact, suevite covered the entire floor of the impact basin. Suevite thickness is 100-165 m on the top of the peak ring but 200 m in-the central basin, suggesting that suevite flowed downslope from the collapsing central uplift during and after peak-ring formation, accumulating preferentially within the central basin.

Central uplift collapse in acoustically fluidized granular targets: Insights from analog modeling

“…Numerical simulations of impact cratering successfully reproduce the morphology of the Chicxulub impact structure ) and planetary peak-ring craters in general. Also, results from the IODP-ICDP Expedition 364 (Christeson et al 2018) are consistent with the numerical model: the presence of uplifted shocked rocks in the peak-ring as predicted by numerical simulations could be confirmed and the movements of the involved rocks could be reconstructed based on successive rotations of shock indicators and the timing of deformation events Riller et al 2018;Rae et al 2019aRae et al , 2019b. Moreover, the important role of a temporary strength degradation could be demonstrated during uplift and collapse of the central peak.…”

“…Also, results from the IODP‐ICDP Expedition 364 (Christeson et al. ) are consistent with the numerical model: the presence of uplifted shocked rocks in the peak‐ring as predicted by numerical simulations could be confirmed and the movements of the involved rocks could be reconstructed based on successive rotations of shock indicators and the timing of deformation events (Morgan et al. ; Riller et al.…”

Imaging the Shallow Subsurface Structure of the North Hikurangi Subduction Zone, New Zealand, Using 2‐D Full‐Waveform Inversion

“…Given this approximation, we can expect there to be some inaccuracies in the recovered P wave model; for example, if anisotropy is not accounted for, FWI velocity models are stretched and the depths inaccurate. This was observed in the recent drilling of the Chicxulub impact crater, where FWI‐determined (subhorizontal) velocities obtained prior to drilling (Morgan et al, ) led to an overestimate in the vertical velocity within the sedimentary overburden and corresponding depth to the crater (Christeson et al, ).…”

“…In addition, the reflection section represents the vertical differential of the perfect velocity model, and differentiation enhances the shorter wavelengths so that reflections sections are always rougher/sharper than their corresponding velocity models even when their nominal bandwidths are the same. Finally, as the FWI is isotropic (Table ), any anisotropy in the subsurface will not be accounted for, which means that we also expect to see an offset in depth between individual reflections, which are more sensitive to changes in vertical velocity, and the velocity anomalies recovered by FWI, which are more sensitive to the horizontal velocity structure (Bentham et al, ; Christeson et al, ). All of these points mean that we expect the dips and depths of reflectors in the PSDM, to be slightly offset and more smoothed in the FWI velocity model.…”

Malvinas (Falkland) Plateau structure versus Mjølnir crater: Geophysical workflow template for proposed marine impact craters

“…In the paper, we use the term marine impact structures for impacts that occurred in a marine setting and resulted in structures that are currently partially or totally underwater. Of these, the Chicxulub (Gulick et al 2013;Kring et al 2016;Christeson et al 2018), Mjølnir (Gudlaugsson 1993;Dypvik et al 1996, Chesapeake Bay (Koeberl et al 1996;Gohn et al 2006) and Montagnais structures (Jansa et al 1989) are among the most comprehensively documented by geophysical data and/or drilling (Fig. 1a).…”