Target-rock fluidization during peak-ring formation of the Chicxulub Crater inferred from Expedition 364 drill core

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http://meetingorganizer.copernicus.org/EGU2018/EGU2018-3978.pdf
Author(s): Riller, Ulrich; Schulte, Felix; Poelchau, Michael H.; Rae, Auriol; Grieve, Richard; Lofi, Johanna; Morgan, Joanna; McCall, Naoma; Gulick, Sean
Author Affiliation(s): Primary:
Hamburg University, Institute of Geology, Hamburg, Germany
Other:
Freiburg University, Germany
Imperial College London, United Kingdom
Natural Resources Canada, Canada
Université de Montpellier, France
University of Texas at Austin, United States
Volume Title: European Geosciences Union general assembly 2018
Source: Geophysical Research Abstracts, Vol.20; European Geosciences Union general assembly 2018, Vienna, Austria, April 8-13, 2018. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: The floors of large impact structures are largely flat and contain one or more morphological rings. The formation of the innermost topographic ring, the so-called peak ring, and the causes of target rock weakening leading to observed flat crater floors are not well understood. Constraining these mechanisms is the prime structural geological objective of Expedition 364 "Drilling the K-Pg Impact Crater", using the Chicxulub impact structure, Mexico, as a terrestrial analogue for the formation of planetary impact basins. A total of 829 meters of core was recovered from borehole M0077A drilled into the peak ring of the Chicxulub crater. From bottom to top, the core is crudely composed of: (1) pervasively shocked granitoid target rock hosting meter- to decameter-thick impact melt rock and suevite dike-like bodies, (2) a 130 m thick impact melt rock and suevite unit overlying the target rocks, and (3) a 112 m thick section of post-impact pelagic carbonate rocks. Based on visual appraisal of the drill core, we determined prominent impact-induced deformation structures in target rock pertaining to rock fluidization during cratering. In addition to microscopic planar structures formed by shock metamorphism, the target rocks are replete with impact-induced, mesoscopic planar deformation structures. These structures include: (1) cataclastic deformation zones, (2) striated shear faults, (3) crenulated mineral folia-tions, and (4) ductile shear band structures. Structural overprinting criteria point to a relative age for these structures. Zones of cataclasite are consistently displaced or utilized by shear faults. Cataclasite bands in target rock fragments included in suevite are cut by the latter and a striated target rock fragment was found in impact melt rock. Suevite and impact melt were emplaced in zones of dilation, often localized by shear faults. Collectively, these observations suggest that cataclastic deformation was followed by shear faulting, followed in turn by emplacement of suevite and melt into dilation zones. This succession of deformation mechanisms is corroborated by the observation that suevite and impact melt bodies are devoid of cataclasite and shear faults. These lithologies were still viscous when they were deformed by ductile band structures. Thus, the shear band structures formed after the shear faults. Based on the structural overprinting relationships, we attempt to relate the mesoscopic planar structures to cratering stages known from impact mechanics. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; 23 Surficial Geology, Geomorphology; Atlantic Ocean; Breccia; Cataclasites; Cenozoic; Chicxulub Crater; Craters; Cretaceous; Deformation; Expedition 364; Gulf of Mexico; IODP Site M0077; Impact breccia; Impact features; Impact melts; Impactites; International Ocean Discovery Program; K-Pg boundary; Lower Paleocene; Melts; Mesozoic; Metamorphic rocks; North Atlantic; Paleocene; Paleogene; Peak rings; Stratigraphic boundary; Suevite; Tertiary; Upper Cretaceous
Coordinates: N212701 N212701 W0895658 W0895658
Record ID: 2018093351
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany