Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..543v&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 543-544
Other
4
Chondrites, Diamonds, Meteoritic Composition, Nitrogen, Pyrolysis, Rare Gases, Chemical Composition, Diffusion, Mineralogy, Phase Transformations, Temperature Effects
Scientific paper
It has long been known that release of noble gases from Cdelta diamonds is not a pure diffusion process but is accompanied by the release of chemically active gases that suggest that chemical reactions occur between coexisting phases of the sample and its environment. Therefore the release temperatures of noble gases depend on sample purity; for the purest sample of Cdelta the difference between release temperatures of Ne and Xe is very small. This means that the release of noble gases is governed by diamond destruction rather than a diffusion-controlled process. An explanation of the phenomenon suggests reactions between C and oxide minerals, which also survive the chemical treatment during the sample preparation. However, other O sources need to be considered. We present some new thoughts on chemical processes to extend our previous work. In all our pyrolysis experiments with Cdelta samples from CI, CM, CV, and CO meteorites we have observed the release of substantial amounts of C. Chemical analysis of the gas phase at each step reveals C in the form of both CO2 and CO with CO2/CO ratio about 4 at low temperature. Most of the C released from the sample is just in the range where the major portion of HL noble gases are observed, strongly indicating that diamond destruction is the reason for their release. The greater proportion of light N releases well before chemical reactions start to destroy diamond grains effectively. Actually we do not kow the mechanism of N release during diamond pyrolysis. If diffusion is involved for N, we cannot expect it to be released from Cdelta at lower temperature than Ne unless different carriers exist for the light N and HL noble gases.
Pillinger Colin T.
Verchovsky Alexander B.
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