L.J. Patrick Muffler Michael A. Clynne Duane E. Champion Brent D. Turrin 2007 <p>⁴⁰<span>Ar/</span>³⁹<span>Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K</span>₂<span>O can be dated reliably. The HCB underlies &sim;&nbsp;15&nbsp;ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield&nbsp;</span>⁴⁰<span>Ar/</span>³⁹<span>Ar ages of 38&nbsp;&plusmn;&nbsp;7&nbsp;ka (Cinder Butte; 1.65% K</span>₂<span>O), 46&nbsp;&plusmn;&nbsp;7&nbsp;ka (Sugarloaf Peak; 1.85% K</span>₂<span>O), 67&nbsp;&plusmn;&nbsp;4&nbsp;ka (Little Potato Butte; 1.42% K</span>₂<span>O) and 77&nbsp;&plusmn;&nbsp;11&nbsp;ka (Potato Butte; 1.62% K</span>₂<span>O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K</span>₂<span>O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26&nbsp;&plusmn;&nbsp;6&nbsp;ka is seductively appealing. A second sample (0.17% K</span>₂<span>O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26&nbsp;&plusmn;&nbsp;18, 30&nbsp;&plusmn;&nbsp;20 and 24&nbsp;&plusmn;&nbsp;6&nbsp;ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24&nbsp;&plusmn;&nbsp;6&nbsp;ka is preferred. As with all isotopically determined ages, confidence in the results is significantly enhanced when additional constraints imposed by other isotopic ages within a stratigraphic context are taken into account.</span></p> application/pdf 10.1016/j.yqres.2007.02.004 en Elsevier Robust 24 ± 6 ka ⁴⁰Ar/³⁹Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California article