A new high-precision 40Ar/39Ar age for the Rochechouart impact structure : at least 5 Ma older than the Triassic–Jurassic boundary
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The Rochechourt impact structure in south-central France, with maximum diameter of 40–50 km, has previously been dated to within 1% uncertainty of the Triassic–Jurassic boundary, at which time ~30% of global genera became extinct. To evaluate the temporal relationship between the impact and the Triassic–Jurassic boundary at high precision, we have re-examined the structure's age using multicollector ARGUS-V 40Ar/39Ar mass spectrometry. Results from four aliquots of impact melt are highly reproducible, and yield an age of 206.92 ± 0.20/0.32 Ma (2σ, full analytical/external uncertainties). Thus, the Rochechouart impact structure predates the Triassic–Jurassic boundary by 5.6 ± 0.4 Ma and so is not temporally linked to the mass extinction. Rochechouart has formerly been proposed to be part of a multiple impact event, but when compared with new ages from the other purported “paired” structures, the results provide no evidence for synchronous impacts in the Late Triassic. The widespread Central Atlantic Magmatic Province flood basalts remain the most likely cause of the Triassic–Jurassic mass extinction.
Cohen , B E , Mark , D F , Lee , M R & Simpson , S L 2017 , ' A new high-precision 40 Ar/ 39 Ar age for the Rochechouart impact structure : at least 5 Ma older than the Triassic–Jurassic boundary ' Meteoritics & Planetary Science , vol 52 , no. 8 , pp. 1600-1611 . DOI: 10.1111/maps.12880
Meteoritics & Planetary Science
© 2017 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Cohen was supported by STFC grant ST/N000846/1. The funds for 40Ar/39Ar dating were supplied by the SUERC Argon Isotope Facility. NERC are thanked for the continued funding of the Argon Isotope Facility.
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