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

G.L. Christeson (1) , S.P.S. Gulick (1, 2) , J.V. Morgan (3) , C. Gebhardt (4) , D.A. Kring (5) , E. Le Ber (6) , Johanna Lofi (7) , C. Nixon (8) , M. Poelchau (9) , A.S.P. Rae (3) , M. Rebolledo-Vieyra , U. Riller (10) , D.R. Schmitt (8) , A. Wittmann (11) , T.J. Bralower (12) , Elise Chenot (13) , P. Claeys (14) , C.S. Cockell (15) , M.J.L. Coolen (16) , L. Ferrière (17) , S. Green (18) , K. Goto (19) , H. Jones (12) , C.M. Lowery (1) , C. Mellett (20) , R. Ocampo-Torres (21) , L. Perez-Cruz (22) , A.E. Pickersgill (23, 24) , C. Rasmussen (25) , H. Sato (26) , J. Smit (27) , S.M. Tikoo (28) , N. Tomioka (29) , J. Urrutia-Fucugauchi (22) , M.T. Whalen (30) , L. Xiao (31) , K.E. Yamaguchi (32, 33)

1 IG - Institute of Geophysics [Austin]
2 Department of Geological Sciences [Austin]
3 Department of Earth Science and Engineering [Imperial College London]
4 AWI - Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung = Alfred Wegener Institute for Polar and Marine Research = Institut Alfred-Wegener pour la recherche polaire et marine
5 LPI - Lunar and Planetary Institute [Houston]
6 Department of Geology
7 Géosciences Montpellier
8 Department of Physics
9 Department of Geology
10 Institut für Geologie
11 Eyring Materials Center
12 Department of Geosciences
13 BGS - Biogéosciences [UMR 6282]
14 Analytical, Environmental and Geo- Chemistry
15 SUPA School of Physics and Astronomy [Edinburgh]
16 WA-OIGC - WA-Organic and Isotope Geochemistry Centre
17 NHM - Natural History Museum [Vienna]
18 British Geological Survey [Edinburgh]
19 International Research Institute of Disaster Science
20 United Kingdom Hydrographic Office
21 ICPEES - Institut de chimie et procédés pour l'énergie, l'environnement et la santé
22 Instituto de Geofísica
23 School of Geographical and Earth Sciences
24 NERC Argon Isotope Facility [Glasgow]
25 Department of Geology and Geophysics
26 JAMSTEC - Japan Agency for Marine-Earth Science and Technology
27 FALW - Faculty of Earth and Life Sciences [Amsterdam]
28 Department of Earth and Planetary Sciences [Piscataway]
29 Kochi Institute for Core Sample Research
30 Department of Geosciences
31 School of Earth Sciences [Wuham]
32 Department of Chemistry
33 NAI - NASA Astrobiology Institute

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/cm3, 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/cm3, 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/cm3, 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.

Mots clés: Chicxulub peak ring physical properties impact crater

Domaines: Stratigraphie; Géophysique [physics.geo-ph]

G.L. Christeson, S.P.S. Gulick, J.V. Morgan, C. Gebhardt, D.A. Kring, et al.. Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition 364.. Earth and Planetary Science Letters, 2018, 495, pp.1-11. ⟨10.1016/j.epsl.2018.05.013⟩. ⟨hal-01803718⟩