40Ar/36Ar analyses of historic lava flows

Earth and Planetary Science Letters



The ratio40Ar/36Ar was measured for 26 subaerial historic lava flows. Approximately one-third of the samples had40Ar/36Ar ratios either higher or lower than the atmospheric value of 295.5 at the 95% confidence level. Excess radiogenic40Ar in five flows ranged from about 1 × 10−13 to 1.5 × 10−12 mol/g. Possible excess36Ar in three flows was on the order of 10−16 to 10−15 mol/g. Upper 95% confidence limits for excess40Ar in samples with normal40Ar/36Ar ratios are generally less than 3 × 10−13 mol/g. The origin of the excess36Ar is unknown but it may be due either to the incorporation of primitive argon that has been stored in the mantle in very low potassium environments or to enrichment in36Ar as atmospheric argon diffuses into the rocks after they cool.

    Publication type Article
    Publication Subtype Journal Article
    Title 40Ar/36Ar analyses of historic lava flows
    Series title Earth and Planetary Science Letters
    DOI 10.1016/0012-821X(69)90160-5
    Volume 6
    Issue 1
    Year Published 1969
    Language English
    Publisher Elsevier
    Description 9 p.
    First page 47
    Last page 55
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