G. B. Dalrymple 1969 <div id="abstracts" class="Abstracts u-font-serif"><div id="ab1" class="abstract author" lang="en"><div id="aep-abstract-sec-id4"><p>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<span>&nbsp;</span>to 1.5 × 10⁻¹²<span>&nbsp;</span>mol/g. Possible excess³⁶Ar in three flows was on the order of 10⁻¹⁶<span>&nbsp;</span>to 10⁻¹⁵<span>&nbsp;</span>mol/g. Upper 95% confidence limits for excess⁴⁰Ar in samples with normal⁴⁰Ar/³⁶Ar ratios are generally less than 3 × 10⁻¹³<span>&nbsp;</span>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.</p></div></div></div><ul id="issue-navigation" class="issue-navigation u-margin-s-bottom u-bg-grey1"></ul> application/pdf 10.1016/0012-821X(69)90160-5 en Elsevier 40Ar/36Ar analyses of historic lava flows article