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Noble gases in diamonds: Occurrences of solarlike helium and neon

Honda, M. and Reynolds, J. H. and Roedder, E. and Epstein, S. (1987) Noble gases in diamonds: Occurrences of solarlike helium and neon. Journal of Geophysical Research B, 92 (B12). pp. 12507-12521. ISSN 0148-0227. doi:10.1029/JB092iB12p12507.

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We have measured noble gases in 17 diamond samples, mostly inclusion free, from diverse, known locations. The ^3He/^4He ratios are characterized by a large spread (10^4), ranging from values below atmospheric to close to the solar ratio. Highest ratios were seen for an Australian colorless diamond composite and an Arkansas diamond. These samples also have imprecise but intriguing neon isotopic ratios, which are close to the solar value. An origin for the solarlike He and Ne in the diamond samples is unlikely to be accounted for by the presence of nucleogenic or spallogenic components. For single diamond stones a positive correlation is found between ^3He/^4He and ^(13)C/^(12)C, possibly indicating that heavy carbon is accompanied by primordial helium. However, the He result for the Australian colorless diamond composite with low δ^(13)C value requires another explanation, possibly sedimentary carbon contaminated with cosmic dust. The wide variation in ^4He/^(40)_*Ar ratios observed from diamond samples suggests a complex history for the source regions and the diamond crystallization processes. Results for two Australian diamond composites (colorless and colored), which came from the same kimberlite pipe, are especially notable: the colorless stones contain no radiogenic components but solarlike He and Ne isotopic ratios, whereas the colored stones are enriched in radiogenic and fissiogenic components. Seemingly the Australian diamonds crystallized in a heterogeneous environment in the mantle source region. A pair of Arkansas diamonds, believed to be from a single pipe, exhibits similar anomalies.

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Additional Information:© 1987 American Geophysical Union. Received June 16, 1986; revised December 5, 1986; accepted March 3, 1987. We thank G. A. McCrory and M. Poole for important technical assistance. We thank G. Crozaz and especially R. Korotev of the Department of Earth and Planetary Sciences at Washington University, St. Louis, for instrumental neutron activation analyses of one of the gemstones. We thank D. Phinney of the Lawrence Livermore Laboratory for a preliminary lithium and boron analysis of one of the samples and S. P. Smith of Charles Evans & Associates for an attempted uranium analysis. We thank A. Yaniv for helpful discussions about spallogenic production of noble gas isotopes. We thank G. Lux for help with our absolute calibration and for assistance to one of us in writing, and Sandy Ewing and Melissa Stevenson for typing. The isotopic analyses of carbon at the California Institute of Technology were supported in part by the National Science Foundation under grant EAR8504096. The work at Berkeley was supported in part by NASA under grant NAG9-34 and bears code 142. Paper number 6B6135
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Issue or Number:B12
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Official Citation:Honda, M., J. H. Reynolds, E. Roedder, and S. Epstein (1987), Noble gases in diamonds: Occurrences of solarlike helium and neon, J. Geophys. Res., 92(B12), 12507–12521, doi:10.1029/JB092iB12p12507.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44268
Deposited By: Ruth Sustaita
Deposited On:12 Mar 2014 17:51
Last Modified:10 Nov 2021 16:49

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