thumbnail

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

Quaternary Research

By:
, , ,
DOI: 10.1016/j.yqres.2007.02.004

Links

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. ?? 2007 University of Washington.

Additional Publication Details

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
Year Published:
2007
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Quaternary Research
First page:
96
Last page:
110
Number of Pages:
15