Resolving the age of the Haughton impact structure using coupled 40Ar/39Ar and U-Pb geochronology

1,2Timmons M.Erickson,2Christopher L.Kirkland,2,3Fred Jourdan,4Martin Schmieder,2MichaelI. H. Hartnady,2Morgan A.Cox,2Nicholas E.Timms
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.008]
1Jacobs – JETS Contract, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, 77058, USA
2The Institute for Geoscience Research (TIGeR), (Timescales of Mineral Systems Group), School of Earth and Planetary Sciences, Curtin University, GPO Box 1984, Perth, WA, 6845, Australia
3Western Australian Argon Isotope Facility, John de Laeter Centre and Space Science and Technology Centre, Curtin University, GPO Box 1984, Perth, WA, 6845, Australia
4HNU Neu-Ulm University of Applied Sciences, Wileystraße 1, D-89231 Neu-Ulm, Germany
Copyright Elsevier

The Haughton Dome located on Devon Island, in the Canadian Archipelago represents a well-preserved, moderate-sized, complex impact crater. Previous age constraints for the 24 km-diameter impact structure have ranged from ca. 21 Ma to ca. 39 Ma. Herein, we present a coordinated microstructural and in situ U-Pb study of zircon and monazite coupled with 40Ar/39Ar laser step heating of shock-melted K-feldspar clasts from shock metamorphosed gneissic fragments collected from the allochthonous impact breccia at Haughton. Moderately shocked zircon and monazite grains yield an age distribution consistent with an Archean protolith metamorphosed at ca. 1.9 Ga, whereas shock recrystallized zircon and monazite yield a lower intercept age of 31.8 ± 1.7 Ma (n=48, MSWD = 0.58, P = 0.99). Four inverse isochron 40Ar/39Ar ages of shocked feldspar clasts yield a weighted mean age of 31.04 ± 0.37 Ma (MSWD = 0.98, P = 0.40), within uncertainty of the U-Pb lower concordia intercept. Ar diffusion modelling supports the interpretation of the impact age and helps resolve impact-driven age resetting. These results highlight the power of coupling multiple geochronologic techniques for determining impact ages, especially from targets with complex geologic histories. Furthermore, they resolve previous discrepancies in the age of the Haughton Dome and the interpretation of the post impact stratigraphy of the crater fill.

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