(U‐Th)/He zircon dating of Chesapeake Bay distal impact ejecta from ODP site 1073

1M. B. Biren,2J.‐A. Wartho,1M. C. VAN Soest,1K. V. Hodges,3,4H. Cathey,5B. P. Glass,6,7C. Koeberl,8J. W. Horton Jr,9W. Hale
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13316]
1Group 18 Laboratories, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
2GEOMAR Helmholtz Centre for Ocean Research Kiel, D‐24148 Kiel, Germany
3LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona, 84287 USA
4Central Analytical Research Facility, Queensland University of Technology, Brisbane, Queensland, 4000 Australia
5Department of Geological Sciences, University of Delaware, Newark, Delaware, 19716 USA
6Department of Lithospheric Research, University of Vienna, A‐1090 Vienna, Austria
7Natural History Museum, Burgring 7, A‐1010 Vienna, Austria
8U.S. Geological Survey, 926A National Center, Reston, Virginia, 20192 USA
9IODP Core Repository, Bremen, D‐28359 Germany
Published by arrangement with John Wiley & Sons

Single crystal (U‐Th)/He dating has been undertaken on 21 detrital zircon grains extracted from a core sample from Ocean Drilling Project (ODP) site 1073, which is located ~390 km northeast of the center of the Chesapeake Bay impact structure. Optical and electron imaging in combination with energy dispersive X‐ray microanalysis (EDS) of zircon grains from this late Eocene sediment shows clear evidence of shock metamorphism in some zircon grains, which suggests that these shocked zircon crystals are distal ejecta from the formation of the ~40 km diameter Chesapeake Bay impact structure. (U‐Th/He) dates for zircon crystals from this sediment range from 33.49 ± 0.94 to 305.1 ± 8.6 Ma (2σ), implying crystal‐to‐crystal variability in the degree of impact‐related resetting of (U‐Th)/He systematics and a range of different possible sources. The two youngest zircon grains yield an inverse‐variance weighted mean (U‐Th)/He age of 33.99 ± 0.71 Ma (2σ uncertainties n = 2; mean square weighted deviation = 2.6; probability [P] = 11%), which is interpreted to be the (U‐Th)/He age of formation of the Chesapeake Bay impact structure. This age is in agreement with K/Ar, 40Ar/39Ar, and fission track dates for tektites from the North American strewn field, which have been interpreted as associated with the Chesapeake Bay impact event.

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