Nature 325, 335 - 337 (22 January 1987); doi:10.1038/325335a0

Cosmic-ray-produced neon and helium in the summit lavas of Maui

K. Marti^* & H. Craig^†

^*University of California, San Diego, Chemistry Department, B-017, La Jolla, California 92093, USA
^† Scripps Institution of Oceanography, A-020, University of California, San Diego, La Jolla, California 92093, USA

A ³He component attributed to cosmic-ray-induced spallation reactions (³He_c) in silicate minerals has recently been identified in lava flows on the summit of Haleakala volcano on Maui^1–3. This³He_c is observed in the helium extracted by fusion of olivine and pyroxene phenocrysts after first removing almost all of the mantle-derived helium by vacuum-crushing, a procedure which releases the volatiles trapped in fluid inclusions within the phenocrysts. Cosmic-ray-produced ³He was found in the high-altitude (3,000 m) summit lavas, which are 500,000 years old, but was not observed in sub-surface samples which were overlain by younger basalts² or in a 200-yr-old lava flow at sea level on Maui^1,2. We report here the identification of cosmic-ray-produced ²¹Ne_c, in addition to ³He_c, in gases extracted by fusion of olivines and clinopyroxenes after vacuum-crushing. The observed (³He/²¹Ne)_c ratios and the ratio of ²¹Ne_c in olivine to that in clinopyroxene are consistent with an in situ origin of ³He_c and ²¹Ne_c by cosmic-ray spallation reactions. This component could be important for interpreting helium isotopic data in terrestrial reservoirs. Geophysical applications could include determinations of erosion rates and exposure histories of terrestrial rocks.

References

1.	Craig, H. & Poreda, R. J. Proc. natn. Acad. Set. U.S.A. 83, 1970−1974 (1986). | ChemPort |
2.	Kurz, M. D. Nature 320, 435−439 (1986); Terra cogn. 6, 106 (1986).
3.	Craig, H., Poreda, R. J. & Marti, K. Terra cogn. 6, 258 (1986).
4.	Macdonald, G. A. U.S. geol. Surv. misc. Invest. Ser. Map I-1088 (1978).
5.	Eberhardt, P. & Eberhardt, A. Helv. phys. Acta 33, 593−594 (1960). | ChemPort |
6.	Eberhardt, P., Eugster, O. & Marti, K. Z. Naturf. 20a, 623−624 (1965). | ChemPort |
7.	Bogard, D. D. & Cressy, P. J. Jr Geochim. cosmochim. Acta 37, 527−546 (1973). | Article | ChemPort |
8.	Staufler, H. J. geophys. Res. 67, 2023−2028 (1962).
9.	Nishiizumi, K., Lal, D., Klein, J., Middleton, R. & Arnold, J. R. Nature 319, 134−136 (1986). | Article | ISI | ChemPort |