On nature of bimodal release of noble gases during pyrolysis of the meteoritic nanodiamonds |
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Authors: | A V Fisenko L F Semjonova |
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Institution: | 1.Vernadsky Institute of Geochemistry and Analytical Chemistry,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Analysis of noble gas proportions and their release kinetics during stepped pyrolysis and oxidation of meteoritic nanodiamonds,
as well as their core-shell structure led to the following conclusions: (1) Noble gases of HL component with anomalous isotopic
composition were presumably formed prior to implantation in the nanodiamonds owing to mixing of nucleosynthetic products of
p- and r- process associated with explosion of type-II supernova with noble gases having “normal” isotopic composition; (2) isotopically
normal P3 noble gases in the nanodiamonds grains are confined to the nondiamond (for instance, graphite-like) phase in the
surface layer. The “layer” structure of nanodiamonds grains resulted from heating up to 800–900°C. Observed increase in contents
of P3 noble gases with increasing grain sizes of meteoritic nanodiamonds is caused by the dependence of the degree of graphitization
of the superfical layer at given temperature on the grain size and surface defect density; (3) bimodal release of noble gases
during pyrolysis of the meteoritic nanodiamonds from weakly metamorphosed meteorites was caused by P3 and HL components, which
are comparable in abundance but sharply differ in their release temperature. |
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