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40Ar/39Ar ages from the rhyolite of Alder Creek, California: age of the Cobb Mountain normal-polarity subchron revisited

Geology

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Abstract

New 40Ar/39Ar age determinations on sanidine from the rhyolite of Alder Creek, California, indicate a 1.186 ?? 0.006 Ma age for the Cobb Mountain Normal-Polarity Subchron. The hew age is statistically older (?? = 0.05) than the previously reported K-Ar age (1.12 ?? 0.02 Ma) and agrees with the age suggested by the astronomical polarity time scale. Incomplete extraction of radiogenic 40Ar (40Ar*) from the sanidine is the most likely reason for the disparity between the 40Ar/39Ar and K-Ar ages. Because the Cobb Mountain subchron is a worldwide, short-duration event, and because no widely used interlaboratory 40Ar/39Ar standard younger than 27 Ma exists, it is proposed that sanidine from the rhyolite of Alder Creek be considered for use as a new Quaternary 40Ar/39Ar mineral standard. -Authors

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
40Ar/39Ar ages from the rhyolite of Alder Creek, California: age of the Cobb Mountain normal-polarity subchron revisited
Series title:
Geology
Volume
22
Issue:
3
Year Published:
1994
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geology
First page:
251
Last page:
254
Number of Pages:
4