ISOTOPIC ANOMALIES OF NOBLE-GASES IN METEORITES AND THEIR ORIGINS .3. LL-CHONDRITES
ISOTOPIC ANOMALIES OF NOBLE-GASES IN METEORITES AND THEIR ORIGINS .3. LL-CHONDRITES
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DOI：
10.1016/0016-7037(79)90134-0
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发表时间：
1979-01-01
影响因子：
5
通讯作者：
ANDERS, E
中科院分区：
文献类型：
--
作者：
ALAERTS, L;LEWIS, RS;ANDERS, E
用选择性腐蚀技术研究了9种低硫铝土矿，确定了三种矿物组分中的贵气组分：HF-HCl可溶物（硅酸盐、金属、硫铁矿等）;占陨石总量的1.99%）、铬铁矿和碳（1.0000.3 -0.7%）和Q（一种特征不佳的矿物，其在HNO 3中的溶解度定义为，占陨石总量的1.000.05%，但含有大部分Ar、Kr、Ar和氖成分，20 Ne 22 Ne= 10.9±0.8）。在Q福尔斯的20 Ne 36 Ar比下降的岩石类型和上升的36 Ar含量，预期冷凝从冷却的太阳星云，但与预期的趋势变质损失。因此，不同岩石学类型的球粒陨石不可能都来自同一个富含挥发分的祖先，而是必须在一个温度范围内形成，相应地具有不同的固有挥发分含量。碳质球粒陨石裂变（CCFs）组分随岩石类型而系统变化。最原始的LL 3（Krymka、Bishunpur、Chainpur）在铬铁矿碳中含有大量的CCF 3，相对于原始的CCF 3富集，如高136 <$132 <$（0.359-0.459，原始的CCF 3为0.310）所示。这些伴随着He和Ne（20 Ne 22 Ne≈ 8.0）以及可变数量的富含轻同位素的氙成分。这些陨石中的铬铁矿成分特殊，含有大量的Fe（III）。这些陨石，以及Parnallee（LL 3）和哈姆雷特（LL 4）也含有Q相的CCF 3，被原始的CCF 3（136 <$132 <$= 0.317-0.329）严重稀释。另一方面，LL 5和LL 6（Olivenza，St. Séverin，Manbhoom和Dhurmsala）中的两种矿物都不含CCF 3，这种缺陷一定是内在的，而不是变质损失造成的，因为这些陨石中的Q仍然含有大量的原始Ne。如果CCF 3来自超新星，那么它在LL-陨石中的分布需要三种具有正确溶解度特性的前太阳载体矿物，其中包含三种不同的氙成分。这些矿物必须适当地分布在岩石类型上，与当地产生的含原始气体的Q一起，并且它们必须是同位素正常的，与它们所含的气体相反。另一方面，如果CCF 3来自一种挥发性超重元素的裂变，那么它从LL 3到LL 6的减少可以归因于太阳星云逐渐不完全的凝聚。特设的假设必须的主机相Q，其协会与铁铬铁矿和起源的相关氙组分富集轻同位素。LL 3和LL 4中的可溶性矿物质含有以前未观察到的太阳氙成分，然而，它不是来自太阳风。因此，三种类型的“原始”氙并排出现在同一陨石的不同矿物中：铁铬铁矿和碳中的强烈分馏氙，Q相中的轻微分馏氙和可溶物中的“太阳能”氙。因为前两个显然可以通过质量分馏从第三个衍生出来，所以看起来很可能都是从同一个太阳星云库中捕获的，但质量分馏的程度不同。
Nine LL-chondrites were studied by a selective etching technique, to characterize the noblegas components in three mineral fractions: HF-HCl-solubles (silicates, metal, troilite, etc.; comprising∼ 99% of the meteorite), chromite and carbon (∼ 0.3–0.7%) and Q (a poorly characterized mineral defined by its solubility in HNO 3, comprising∼ 0.05% of the meteorite but containing most of the Ar, Kr, Xe and a neon component of 20 Ne 22 Ne= 10.9±0.8). The 20 Ne 36 Ar ratio in Q falls wi petrologic type and rising 36 Ar content, as expected for condensation from a cooling solar nebula, but contrary to the trend expected for metamorphic losses. Chondrites of different petrologic types therefore cannot all be derived from the same volatile-rich ancestor, but must have formed over a range of temperatures, with correspondingly different intrinsic volatile contents. The CCFXe (carbonaceous chondrite fission) component varies systematically with petrologic type. The most primitive LL3s (Krymka, Bishunpur, Chainpur) contain substantial amounts of CCFXe in chromite-carbon, enriched relative to primordial Xe as shown by high 136 Xe 132 Xe (0.359–0.459, vs 0.310 for primordial Xe). These are accompanied by He and by Ne with 20 Ne 22 Ne≈ 8.0 and by variable amounts of a xenon component enriched in the light isotopes. The chromite in these meteorites is compositionally peculiar, containing substantial amounts of Fe (III). These meteorites, as well as Parnallee (LL3) and Hamlet (LL4) also contain CCFXe in phase Q, heavily diluted by primordial Xe (136 Xe 132 Xe= 0.317–0.329). On the other hand, LL5s and 6s (Olivenza, St. Séverin, Manbhoom and Dhurmsala) contain no CCFXe in either mineral. This deficiency must be intrinsic rather than caused by metamorphic loss, because Q in these meteorites still contains substantial amounts of primordial Ne. If CCFXe comes from a supernova, then its distribution in LL-chondrites requires three presolar carrier minerals of the right solubility properties, containing three different xenon components in certain combinations. These minerals must be appropriately distributed over the petrologic types, together with locally produced Q containing primordial gases, and they must be isotopically normal, in contrast to the gases they contain. On the other hand, if CCFXe comes from fission of a volatile superheavy element, then its decrease from LL3 to LL6 can be attributed to progressively less complete condensation from the solar nebula. Ad hoc assumptions must of the host phase Q, its association with ferrichromite and the origin of the associated xenon component enriched in the light isotopes. Soluble minerals in LL3s and LL4s contain a previously unobserved, solar xenon component, which, however, is not derived from the solar wind. Three types of ‘primordial’xenon thus occur side-by-side in different minerals of the same meteorite: strongly fractionated Xe in ferrichromite and carbon, lightly fractionated Xe in phase Q, and ‘solar’Xe in solubles. Because the first two can apparently be derived from the third by mass fractionation, it seems likely that all were trapped from the same solar nebula reservoir, but with different degrees of mass fractionation.