^1,2Elizabeth J. Catlos,¹Andrew F. Parisi,¹Michael E. Brookfield,³Timmons Erickson,^1,2Sean P.S. Gulick,^4,5Axel K. Schmitt,^1,2Daniel F. Stockli,⁶Daniel P. Miggins,⁷Ben Ruchte,¹Mark Cloos
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70191]
¹Department of Earth & Planetary Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas,USA
²Center for Planetary Systems Habitability, The University of Texas at Austin, Austin, Texas, USA
³Amentum – JETS II, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston,Texas, USA
⁴Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany
⁵John de Laeter Centre, Curtin University, Bentley, Western Australia, Australia
⁶College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA
⁷IXRF, Inc., Austin, Texas, USA
Published by arrangement with John Wiley & Sons

The Ames impact structure (Oklahoma) is thought to have formed during the Ordovician Meteor Event, based on conodont biostratigraphy of its crater fill. Here, U–Pb zircon dates from its impact-melt portion, conducted using secondary ion mass spectrometry and laser ablation–inductively coupled plasma–mass spectrometry (n = 37 spots), yield a Mesoproterozoic emplacement age for the impacted granodiorite (1401.2 ± 8.1 Ma, ±2σ, upper Concordia intercept). However, the youngest zircon dates define a weighted mean age of 369.7 ± 5.9 Ma (n = 10/11), with MSWD = 0.71 and p(χ²) = 0.7. Cathodoluminescence and electron backscattered diffraction images reveal that most zircons, including the youngest Devonian-age grains, show primary oscillatory zoning and lack deformation. However, two have impact-related textures, including regions of low-angle grain boundaries within microcracks and discrete arrays of granular zircon crosscutting oscillatory growth zoning. Plagioclase (n = 6 samples, ⁴⁰Ar/³⁹Ar) yields Late Carboniferous (~310.5 Ma) and Permian (~250.5 Ma) approximate total fusion dates that overlap the timing of heating and hydrocarbon maturation in the crater, suggesting the argon system records postimpact thermal overprinting. Based on the youngest zircon dates, the Ames impact structure may record activity near the Frasnian–Famennian boundary, contemporaneous with other North American impacts.