¹M.B. Biren, ¹M.C. van Soest, ^1,2J.-A. Wartho, ¹K.V. Hodges, ³J.G. Spray
Earth and Planetary Science Letters 453, 56–66 Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.07.053]
¹Group 18 Laboratories, School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
²GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, D-24148 Kiel, Germany
³Planetary and Space Science Centre, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada
Copyright Elsevier

The (U–Th)/He method has been applied to constrain the formation ages of the Clearwater West and East impact structures of Quebec, Canada. Zircons were separated from impact melt samples derived from a surface exposure at Clearwater West (32 km diameter), and from a drill core at Clearwater East (26 km diameter). The (U–Th)/He results indicate ages of 280±27 Ma280±27 Ma (2σ , n=7n=7) for Clearwater West, and 450±56 Ma450±56 Ma (2σ , n=8n=8) for Clearwater East. Our (U–Th)/He date for Clearwater West supports the findings of previous Rb–Sr (266±15 Ma266±15 Ma; 2σ) and 40Ar/39Ar (280±4 Ma280±4 Ma and 283.8±2.2 Ma283.8±2.2 Ma, 2σ) impact melt studies. Our (U–Th)/He date for Clearwater East also overlaps with previously published 40Ar/39Ar dating results, which yielded U-shaped spectra, with ‘maximum’ and ‘best-estimate’ dates of ∼ 460–470 Ma. Our results support the contention, previously based solely on 40Ar/39Ar data, that the Clearwater West and East impact structures do not comprise an impact doublet that formed coevally from a binary asteroid pair.