Primordial noble gases in separated meteoritic minerals,II |
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Authors: | Gregory F Herzog Edward Anders |
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Institution: | 1. Enrico Fermi Institute, University of Chicago, Chicago, Ill. USA;2. Department of Chemistry, University of Chicago, Chicago, Ill. USA |
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Abstract: | Eight silicate samples from the Orgueil carbonaceous chrondrite were analyzed for He, Ne, Ar, and Xe by a stepwise heating technique. Six of the samples, including two etched with NaOH, were density fractions covering the following ranges: < 2.35, 2.35–2.45, 2.45–2.48, and > 2.48 g/cm3. Two others were grain-size fractions, separated according to their ability to form a colloid at pH 11.5.All fractions are grossly deficient in cosmogenic neon, having retained only 8–33% of their normal complement. Retentivity increases with density.All fractions give low20Ne/22Ne ratios above 950°C, suggestive of D.C. Black's exotic “Neon-E” component of20Ne/22Ne ≤ 3.4. The lowest ratios were found in the low-density and especially the non-colloidal fractions. This suggests that the host phase of Ne-E is a clay mineral of lower iron content and coarser grain size than the main silicates of Orgueil.The main fraction,ρ = 2.35–2.45g/cm3, is inhospitable to Xe; it contains less Xe and releases it more readily at low temperatures (30–35% in 1 hour at 550°C) than do any of the other fractions. |
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