Primordial noble gases in "phase Q" in carbonaceous and ordinary chondrites studied by closed-system stepped etching
Primordial noble gases in "phase Q" in carbonaceous and ordinary chondrites studied by closed-system stepped etching
复制标题
DOI：
10.1111/j.1945-5100.2000.tb01485.x
复制
发表时间：
2000-09-01
影响因子：
2.2
通讯作者：
Wieler, R
中科院分区：
文献类型：
--
作者：
Busemann, H;Baur, H;Wieler, R
为了更好地表征原始稀有气体的主要载体“Q相”中的稀有气体，采用封闭系统步进蚀刻（CSSE）测量了CM2 Cold Bokkeveld、CV3 (ox.) Grosnaja、CO3.4 Lance、CO3.7 Isna、LL3.4 Chainpur和H3.7 Dimmitt球粒球粒的耐HF/ hcl残基。除（Ne-20/Ne-22）(Q)外，不同陨石的Q相同位素比值基本一致。正如早期的精确测量（Schelhaas et al., 1990; Wieler et al., 1991,1992）所表明的那样，（Ne-20/Ne-22）(Q)是Q惰性气体中最不均匀的同位素比率。Cold Bokkeveld和Lance的数据簇类似于10.1，Chainpur、Grosnaja和Dimmitt的数据簇类似于10.7。（20Ne/22Ne）(Q)与陨石的分类和蚀变历史没有相关性。所有6个样品的Ar、Kr和Xe同位素比例在其不确定度内是相同的，并且与早期的Q测定以及铀中的Ar-Xe相似。因此，一个未知的过程可能解释了原来合并的Ne-Q的变化。稀有气体元素组成证明，Q至少由两种化学性质稍有不同的碳质载体相“Q(1)”和“Q(2)”组成。比值（Ar/Xe）(Q)和（Kr/Xe）(Q)反映了热变质作用和水蚀变作用。这些母体过程导致了相对于Xe的更大的Ar和Kr消耗。相比之下，遭受严重含水蚀变的陨石，如CM球粒陨石，并没有显示出He和Ne相对于Ar的消耗，而是显示出最高的（He/Ar）(Q)和（Ne/Ar）(Q)比率。这表明Q(1)比Q(2)更不易受水蚀的影响。这两个亚相很可能包含了来自同一个储层的惰性气体，这一点可以从相对于太阳的丰度，较轻的惰性气体的消耗几乎是恒定的（尽管非常大）来说明。然而，元素比表明Q(1)和Q(2)获得（或失去）稀有气体的元素比例略有不同。Cold Bokkeveld认为Q(1)可能与前太阳石墨有关。阶段Q(1)和Q(2)可能与Gros和Anders（1977）提出的子阶段有关。Ne-20/N-22比值的分布不能归因于Q(1)和Q(2)载流子。Chainpur和Cold Bokkeveld的残基中含有大量Ne-E(L)，数据证实了Huss（1997）的建议，即Ne-22-E(L)含量以及太阳系前石墨丰度与陨石的变质历史有关。
The HF/HCl-resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lance, CO3.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed-system stepped etching (CSSE) in order to better characterise the noble gases in "phase Q", a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (Ne-20/Ne-22)(Q). As already suggested by precise earlier measurements (Schelhaas et al., 1990; Wieler et al., 1991, 1992), (Ne-20/Ne-22)(Q) is the least uniform isotopic ratio of the Q noble gases. The data cluster similar to 10.1 for Cold Bokkeveld and Lance and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of (20Ne/22Ne)(Q) with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar-Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne-Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases "Q(1)" and "Q(2)" with slightly distinct chemical properties. Ratios (Ar/Xe)(Q) and (Kr/Xe)(Q) reflect both thermal metamorphism and aqueous alteration. These parent-body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)(Q) and (Ne/Ar)(Q) ratios. This suggests that Q(1) is less susceptible to aqueous alteration than Q(2). Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q(1) and Q(2) must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q(1) may be related to presolar graphite. Phases Q(1) and Q(2) might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the Ne-20/N-22 ratios cannot be attributed to the carriers Q(1) and Q(2) The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne-E(L), and the data confirm the suggestion of Huss (1997) that the Ne-22-E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.