| Autor: |
G. W. Reed, S. Jovanovic |
| Rok vydání: |
1990 |
| Předmět: |
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| Zdroj: |
Chemical Geology: Isotope Geoscience section. 80:181-191 |
| ISSN: |
0168-9622 |
| DOI: |
10.1016/0168-9622(90)90027-a |
| Popis: |
196Hg and 202Hg isotopes measured by neutron activation analysis have been found to have ratios differing from normal in some lunar and meteoritic matter. Some Hg fractions extracted by stepwise heating from several samples of Apollo-14 breccia 14305 and one sample of 14321 exhibit deviations from the normal isotopic ratio by ∼ 20–30%. Samples from three Antarctic basaltic achondrites contain 196Hg202Hg ratios that are lower than normal by factors of 2–4. The anomalies in these meteorites and the temperature fractions in which they occur are reproducible. The anomalous Hg occurs in a single but variable temperature fraction from 14305 samples but only in the 130°C fraction from the three achondrites; data on two of the Antarctic achondrites have been published. The amount of Hg in the fractions with anomalous ratios varied from 10% to ∼ 0.1 % in samples with total Hg of 2–200 ppb. The other 5 to 6 thermally extracted Hg fractions per sample have normal ratios. These fractions act as internal standards and thus serve to reduce uncertainties related to neutron flux variables and sample matrix effects. The anomalous Hg is found in samples from three possible parent bodies: the Moon, that of the shergottites and that of the eucrites. The final thermal evolution of the samples occurred over a time-span ranging from < l.3 to ⩾ 3.9 Ga ago. These facts present obstacles to understanding how this anomalous Hg was acquired; a possible explanation is periodic encounters of the solar system with a dense cloud of interstellar dust containing such Hg. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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