Robust 24 ± 6 ka 40Ar/39Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California
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Abstract
40Ar/39Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K2O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield 40Ar/39Ar ages of 38 ± 7 ka (Cinder Butte; 1.65% K2O), 46 ± 7 ka (Sugarloaf Peak; 1.85% K2O), 67 ± 4 ka (Little Potato Butte; 1.42% K2O) and 77 ± 11 ka (Potato Butte; 1.62% K2O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K2O) 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% K2O) 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.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Robust 24 ± 6 ka 40Ar/39Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California |
| Series title | Quaternary Research |
| DOI | 10.1016/j.yqres.2007.02.004 |
| Volume | 68 |
| Issue | 1 |
| Publication Date | January 20, 2017 |
| Year Published | 2007 |
| Language | English |
| Publisher | Elsevier |
| Contributing office(s) | Volcano Hazards Program |
| Description | 15 p. |
| First page | 96 |
| Last page | 110 |
| Country | United States |
| State | California |
| Other Geospatial | Hat Creek Basalt |
| Online Only (Y/N) | N |
| Additional Online Files (Y/N) | N |