Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29s.513o&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 513-514
Other
1
Abundance, Meteoritic Composition, Pyrolysis, Xenon Isotopes, Phase Transformations, Pressure Measurement, Radioactive Age Determination, Volatility
Scientific paper
Using a combination of pyrolysis and combustion we extracted noble gases from a bulk sample of ALH 85085. If a clear separation of isotopically diverse components were possible by this approach, it would be valuable for the study of meteorites that are in such short supply. Major release of Xe occurs not during combustion, but rather during the preceding pyrolysis steps, which may be taken to indicate that most of Xe is carried by silicates rather than carbonaceous phases. However, release of volatiles also peaks in these same steps, possibly because of reactions of carbonaceous with other, O-bearing, phases, and a clear distinction is not feasible. Since volatiles surviving our extraction process in gaseous form are essentially only CO and CO2, we infer from pressure measurements a C content of approximately 1.05%. Total Xe-136/Xe-132 is 0.3145 +/- 0013, similar to what is found in ordinary chondrites or ureilites. Combustion at 550 and 600 C releases Xe with enhanced Xe-136/Xe-132, probably from Xe-HL. Xenon with very low Xe-136/Xe-132 (approximately 0.305) similar to Xe measured in bulk ALH 85085 (split 22) is observed only in the last two extraction steps that account for approximately 4% of total Xe. Also, compared to the results of Euqster and Niedermann (1990), we find only about half the concentrations of He-4 and Ar-40. In addition, our data do not show evidence for the presence of solar Ne. Data points for the first 10 steps lie approximately on a single straight line connecting to a spallogenic component with Ne-21/Ne-22 approximately 0.9. For the normal shielding conditions thus indicated and published elemental abundances, the Ne-21 production rate is 0.282 cu cm STP/g-m.y., hence the resulting exposure age of 1.5 m.y.
Loehr H. P.
Ott Ulrich
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