Abstract

⁴⁰Ar/³⁹Ar dating of the Central Plateau Member lavas of the Yellowstone Plateau volcanic field is used to evaluate discordant dates in the existing K-Ar dataset. The ⁴⁰Ar/³⁹Ar method identifies several sources of anomalous behavior; xenocrystic contamination, excess argon, and argon loss that influence assessments of the eruption ages. Single crystal dating, multiple sample runs, and statistical evaluation of the multiple analyses are used to assign eruption ages for the following lavas; 87±12 ka (Pitchstone Plateau), 90±10 ka (Grants Pass), 94±21 ka (West Yellowstone), 108±7 ka (Gibbon River), 106±7 ka (Solfatara), 122±5 ka (Hayden Valley), and 135±11 ka (Summit Lake).

The resulting interpreted eruptive ages provide a better understanding of stratigraphic relations, magma residence times, and eruptive histories. Interpretation of the West Yellowstone eruptive age suggests that about half the volume from CPM lavas erupted from a combination of this flow with the Grants Pass and Pitchstone Plateau flows at ~90 ka. The assigned ages in this study support Vazquez and Reed’s (2002) interpretation of significant residence time between crystallization of zircon and sanidine up to 80,000 years for some flows. The revised ages indicate a 15 ka eruptive reoccurrence interval centered around ages of 90 ka, 107 ka, 122 ka, 135 ka, 150 ka, and 165 ka for lavas of Central Plateau and Mallard Lake Members.