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    Ar-40/Ar-39 age of the Lake Saint Martin impact structure (Canada) - unchaining the late Triassic terrestrial impact craters

    Access Status
    Fulltext not available
    Authors
    Schmieder, M.
    Jourdan, Fred
    Tohver, E.
    Cloutis, E.
    Date
    2014
    Type
    Journal Article
    
    Metadata
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    Citation
    Schmieder, M. and Jourdan, F. and Tohver, E. and Cloutis, E. 2014. Ar-40/Ar-39 age of the Lake Saint Martin impact structure (Canada) - unchaining the late Triassic terrestrial impact craters. Earth and Planetary Science Letters. 406: pp. 37-48.
    Source Title
    Earth and Planetary Science Letters
    DOI
    10.1016/j.epsl.2014.08.037
    ISSN
    0012-821X
    School
    Department of Applied Geology
    URI
    http://hdl.handle.net/20.500.11937/32224
    Collection
    • Curtin Research Publications
    Abstract

    New 40Ar/39Ar dating of impact-melted K-feldspars and impact melt rock from the ~40 km Lake Saint Martin impact structure in Manitoba, Canada, yielded three plateau ages and one mini-plateau age in agreement with inverse isochron ages for the K-feldspar melt aliquots and a minimum age for a whole-rock impact melt sample. A combination of two plateau ages and one isochron age, with a weighted mean of 227.8±0.9 Ma227.8±0.9 Ma [±1.1 Ma; including all sources of uncertainty] (2σ ; MSWD = 0.52; P=0.59P=0.59), is considered to represent the best-estimate age for the impact. The concordant 40Ar/39Ar ages for the melted K-feldspars, derived from impact melt rocks in the eastern crater moat domain and the partially melted Proterozoic central uplift granite, suggest that the new dates accurately reflect the Lake Saint Martin impact event in the Carnian stage of the Late Triassic. With a relative error of ±0.4% on the 40Ar/39Ar age, the Lake Saint Martin impact structure counts among the most precisely dated impact structures on Earth. The new isotopic age for Lake Saint Martin significantly improves upon earlier Rb/Sr and (U–Th)/He results for this impact structure and contradicts the hypothesis that planet Earth experienced the formation of a giant ‘impact crater chain’ during a major Late Triassic multiple impact event.

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