Abstract
The absolute cosmogenic production of 21Ne (21Nec) and 3He (3Hec) in olivine (Fo81) is measured for the well‐dated Tabernacle Hill flow. Values scaled to sea level and high latitude ( > 60°) are 45 atoms/g/yr for 21Nec and 109 atoms/g/yr for 3Hec for the past 17,800 years.Production rates for 21Nec are about 50% higher than the theoretical values given by Lal [1991]. A ratio of 21Nec/3Hec of 0.41 ± 0.05 is measured in olivines that have a range of 25 in cosmogenic exposure; there is no evidence of 3Hec loss in samples older than 100,000 years.Volcanic plagioclase is shown to be a suitable mineral for cosmogenic 21Nec dating of surfaces. 21Nec in co‐existing plagioclase and olivine phenocrysts have a constant ratio of 0.42 ± .04 in samples with more than 106 atoms of 21Nec. Using all of the 21Nec data and the 3Hec as a cosmic ray flux monitor, production of 21Nec in Ab36 plagioclase is calculated at 16.8 ± 1.7 atoms/g‐yr for the past 17,800 years. The production of 21Nec from 23Na is estimated at 160 ± 50 atoms/g/yr at 60° and sea level or equivalent to that on 24Mg.
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