Birth of the presolar nebula: The sequence of condensation revealed in the Allende meteorite
Birth of the presolar nebula: The sequence of condensation revealed in the Allende meteorite
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太阳前星云的诞生：阿连德陨石揭示的凝结序列
DOI：
10.1007/bf00648496
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
D. Wark
中科院分区：
文献类型：
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作者：
D. Wark
这项工作适用于著名的太阳系形成的超新星触发假说，详细解释了阿连德陨石的许多属性。阿连德碳质球粒陨石是由毫米至厘米大小的富钙铝包体（CAI's）、细粒富碱尖晶石聚集体、变形橄榄石聚集体、橄榄石球粒和硫化物球粒组成的组合，它们位于极细粒的黑色基质中。详细的同位素、化学和结构性质表明，这些组分以上述顺序形成为独立的宇宙颗粒。一些CAI含有微米级的金属块，其中通常不相容的耐火材料（Mo，Re，W）和铂族（Pt，Os，Ir，Ru）金属以近似“宇宙”的比例合金在一起，这表明这些金块也凝聚成宇宙颗粒。从以上列表中早期成分在后期成分中的一致模式来看，似乎在这些材料形成的环境中，凝析作用的方向是：橄榄石含量增加，难熔元素和16 O含量减少（从16 O过剩的0.4%到16 O“正常”的陆源氧同位素组成）。凝结序列都是短暂而不完整的，由此可以得出结论，凝结物质很快就从凝结环境中分离出来，并被隔离，直到所有物质都聚集在一起，形成最终的“暴风雪”，由细颗粒的橄榄石晶体构成陨石基质。这些主要性质可以在一个模型中解释，在这个模型中，超新星遗迹（SNR）处于“雪犁”阶段，其氧气最初是纯的16 O，推入黑暗的星际云中。在这个模型中，CAI的凝结开始于SNR壳层中，当它被来自云的质量的2500倍稀释时，这也部分解释了在CAI中观察到的同位素异常的罕见性。云对信噪比的延迟推动凝聚的颗粒在它们自己的动量下向云前进。云的持续稀释和颗粒中最难熔元素的持续去除可以解释连续冷凝物中难熔元素（包括REE）的分馏和贫化的演变模式。该模型还能满足CAI上的边缘和细颗粒集料的同心环带等特征。太阳前起源和短（10000年）的碳质玄武岩中的包裹体的形成时间是该模型的主要影响。
This work applies the well-known supernova-trigger hypothesis for solar system formation to explain in detail many properties of the Allende meteorite. The Allende carbonaceous chondrite meteorite is an assemblage of millimetre- to centimetre-sized Ca-Al-rich inclusions (CAI's), fine-grained alkali-rich spinel aggregates, amoeboid olivine aggregates, olivine chondrules and sulfide chondrules set in an extremely fine-grained black matrix. Detailed isotopic, chemical and textural properties show that these components formed in the above order as independent cosmic grains. Some CAI's containmicron-sized metal nuggets in which the normally incompatible refractory (Mo, Re, W) and platinum group (Pt, Os, Ir, Ru) metals are alloyed together in approximately ‘cosmic’ proportions, suggesting that these nuggets also condensed as cosmic grains.From the consistent pattern of enclosure of earlier components on the above list within later ones, it appears that in the environment where these materials formed, condensation moved inexorably in the direction of increasing olivine and decreasing refractory element and16O content (from ∼4% excess16O to ∼‘normal’ terrestrial oxygen isotopic composition). Condensation sequences are all short and incomplete, from which it is concluded that condensing materials were soon separated from the condensing environment and isolated until all were brought together in a final ‘snowstorm’ of fine-grained, olivine crystals constituting the meteorite matrix.These major properties can be accounted for in a model in which a supernova remnant (SNR) in the ‘snowplow’ phase, whose oxygen was initially pure16O, pushes into a dark interstellar cloud. In the model, condensation of CAI's begins in the SNR shell when it has been diluted with ∼2500 times its mass of matter from the cloud, which also in part explains the rarity of observed isotopic anomalies in CAI's. The retardation of the SNR by the cloud propels condensed grains ahead toward the cloud under their own momentum. Continuing dilution by the cloud and continuing removal of the most refractory elements in grains can explain the evolving patterns of fractionation and depletion of refractory elements, including REE's, in successive condensates. Features such as rims on CAI's and concentric zonation of fine-grained aggregates can also be satisfied in the model. A presolar origin and a short (∼ 10 000 years) formation time for inclusions in carbonaceous chondrites are major implications of the model.