Noble gases in separated meteoritic minerals - Murchison /C2/, Ornans /C3/, Karoonda /C5/, and Abee /E4/
Noble gases in separated meteoritic minerals - Murchison /C2/, Ornans /C3/, Karoonda /C5/, and Abee /E4/
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分离陨石矿物中的稀有气体 - Murchison /C2/、Ornans /C3/、Karoonda /C5/ 和 Abee /E4/
DOI：
10.1029/jb082i005p00762
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发表时间：
1977
影响因子：
--
通讯作者：
E. Anders
中科院分区：
文献类型：
--
作者：
B. Srinivasan;J. Gros;E. Anders
通过将陨石溶解在HF-HCl中制备了四种陨石的耐酸矿物馏分，并通过质谱法分析了He，Ne，Ar，Kr和H2O。虽然它们只占陨石的0.1-2.2%，但这些残留物含有高达80%的惰性气体。高富集一般与高铬含量的残留物。为了确定惰性气体成分在各个矿物中的分布情况，采用逐步加热或选择性破坏各个相等技术对几种残留物进行了更详细的检查。在Murchison C2球粒陨石中，约80%的Ar、Kr和Ar+以及约50%的裂变产物存在于HNO 3可溶相（“Q”，可能是Fe-Ni和Fe-Cr硫化物的混合物）中。Q还包含20 Ne/22 Ne = 6.8的俘获Ne分量。铬铁矿包含大部分同位素组成明显不同的He和Ne（20 Ne/22 Ne = 8.64）和少量较重的气体。剩余的10-20%的气体包含在有机聚合物中。铬铁矿馏分中含有强烈富集的Kr和Kr，推测为裂变重同位素; Kr也富含轻同位素。在相同的假设条件下，Kr和Kr的标称裂变谱与阿连德的标称裂变谱相同，但通过假设已知较少的捕获组分具有更多的分馏成分，可以显著改变标称裂变谱。铬铁矿馏分是惊人的富集在散裂21 Ne，由一个因素的15相对于散装陨石。对于这种富集没有完全令人满意的解释;可以想象，这可能是由于经历了前太阳带电粒子照射的尖晶石杂质。Murchison矿物的含气量比阿连德中相应矿物的含气量高约1个数量级。这可能意味着地层区域的压力较高或温度较低，更可能是前者。相对于大块陨石，奥尔南斯残留物（铬铁矿，据推测也是Q和碳质物质）富含重惰性气体一百多倍。一个被困的Ne成分20 Ne/22 Ne = 9.13也出现了，不再被大块陨石中的散裂Ne所掩盖。Karoonda残渣（镍黄铁矿含量约95%）中捕集气体的富集程度较低，但逐步加热实验表明，捕集气体主要存在于高释放温度（1300° ~ 1600 ° C）的微量矿物中，而不存在于镍黄铁矿（释放温度700° ~ 1000 ° C）中。Abee样品（主要是碳）是最不丰富的四个残留物，但仍然表现出增强捕获的气体在散裂的。
Acid-resistant mineral fractions of four chondrites were prepared by dissolving the meteorites in HF-HCl and were analyzed for He, Ne, Ar, Kr, and Xe by mass spectrometry. Although they comprise only 0.1–2.2% of the meteorites, these residues contained up to 80% of the total noble gases. High enrichments generally correlated with high Cr contents of the residues. To determine the distribution of noble gas components among individual minerals, several residues were examined in more detail by techniques such as stepwise heating or selective destruction of individual phases. In the Murchison C2 chondrite some 80% of the trapped Ar, Kr, and Xe and about 50% of the fission Xe reside in an HNO3-soluble phase (‘Q’, presumably a mixture of Fe-Ni and Fe-Cr sulfides). Q also contains a trapped Ne component of 20Ne/22Ne = 6.8. Chromite contains most of the He and Ne of distinctly different isotopic composition (20Ne/22Ne = 8.64) and lesser amounts of heavier gases. The remaining 10–20% of the gases is contained in the organic polymer. The chromite fraction contains Kr and Xe strongly enriched in presumably fissiogenic heavy isotopes; the Xe is also enriched in light isotopes. Nominal fission spectra of Kr and Xe are identical to those for Allende for the same set of assumptions but can be varied markedly by assuming more fractionated compositions for the poorly known trapped component. The chromite fraction is strikingly enriched in spallogenic 21Ne, by a factor of 15 relative to the bulk meteorite. No wholly satisfactory explanation is available for this enrichment; conceivably, it may be due to a spinel impurity that experienced a presolar charged particle irradiation. The gas contents of the Murchison minerals are about 1 order of magnitude higher than those of the corresponding minerals in Allende. This may imply either a higher pressure or a lower temperature in the region of formation, more likely the former. The Ornans residue (chromite, presumably also Q and carbonaceous matter) was more than a hundredfold enriched in heavy noble gases relative to the bulk meteorite. A trapped Ne component of 20Ne/22Ne = 9.13 also emerged, no longer being masked by spallogenic Ne in the bulk meteorite. The Karoonda residue (∼95% pentlandite) was less enriched in trapped gases, but a stepwise heating experiment showed that the gases were contained mainly in trace minerals of high release temperature (1300°–1600°C), not in pentlandite (release temperature, 700°–1000°C). The Abee sample (mainly carbon) was the least enriched of the four residues but still showed an enhancement in trapped gases over spallogenic ones.