New argon-argon (⁴⁰Ar/³⁹Ar) radiometric age dates from selected subsurface basalt flows at the Idaho National Laboratory, Idaho

In 2011, the U.S. Geological Survey, in cooperation with the U.S. Department of Energy, collected samples for 12 new argon-argon radiometric ages from eastern Snake River Plain olivine tholeiite basalt flows in the subsurface at the Idaho National Laboratory. The core samples were collected from flows that had previously published paleomagnetic data. Samples were sent to Rutgers University for argon-argon radiometric dating analyses.

Paleomagnetic and stratigraphic data were used to constrain the results of the age dating experiments to derive the preferred age for each basalt flow. Knowledge of the ages of subsurface basalt flows is needed to improve numerical models of groundwater flow and contaminant transport in the eastern Snake River Plain aquifer. This could be accomplished by increasing the ability to correlate basalt flow from corehole to corehole in the subsurface. The age of basalt flows also can be used in volcanic recurrence and landscape evolution studies that are important to better understand future hazards that could occur at the Idaho National Laboratory.

Results indicate that ages ranged from 60 ± 16 thousand years ago for Quaking Aspen Butte to 621 ± 9 thousand years ago for State Butte.