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Robust 24 ± 6 ka 40 Ar/ 39 Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California

Brent D. Turrin·L.J. Patrick Muffler·Michael A. Clynne·Duane E. Champion
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Abstract

40 Ar/ 39 Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K 2 O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield 40 Ar/ 39 Ar ages of 38 ± 7 ka (Cinder Butte; 1.65% K 2 O), 46 ± 7 ka (Sugarloaf Peak; 1.85% K 2 O), 67 ± 4 ka (Little Potato Butte; 1.42% K 2 O) and 77 ± 11 ka (Potato Butte; 1.62% K 2 O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K 2 O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26 ± 6 ka is seductively appealing. A second sample (0.17% K 2 O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26 ± 18, 30 ± 20 and 24 ± 6 ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24 ± 6 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.

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Quaternary ResearchArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 39.76210275375137° to 41.20758898181025° latitude; -121.4373779296875° to -120.00915527343749° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Brent D. Turrin, L.J. Patrick Muffler, Michael A. Clynne, Duane E. Champion. 2017-01-20. Robust 24 ± 6 ka 40 Ar/ 39 Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California. https://doi.org/10.1016/j.yqres.2007.02.004

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