High‐precision SIMS analyses of seven spinel‐rich fine‐grained CAIs from the CV3 chondrites Efremovka, Kaba, and Vigarano and the LL3.0 chondrite Semarkona, two known to have volatility‐fractionated Group II REE patterns (likely condensates) and three more probably Group II, all give initial ²⁶Al/²⁷Al (²⁶Al/²⁷Al₀) close to the solar system initial value of 5.2 × 10^–5. Our data thus provide no evidence for multiple condensation events in the early solar system. Other work by Ushikubo et al. (2017) and Kawasaki et al. (2019a, 2019b) did find some similar inclusions whose values are significantly lower than the solar system initial value. Because the latter data are too few to indicate whether or not the lower ratios cluster or rather spread out over a range, more work will be required to determine if nebular condensation occurred following only a few major, punctuated thermal events or rather happened more frequently. Regardless, it is now clear that CAIs having the Group II REE pattern formed very early in solar system history, contemporaneous with the formation of CAIs having unfractionated REE patterns. Whatever the mechanism that formed Group II, it occurred under conditions that caused spinel to condense prior to (at a higher temperature than) melilite. This is contrary to the predictions of equilibrium nebular condensation.

中文翻译：

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尖晶石富集的CAI的Al-Mg同位素研究

高精度SIMS分析了来自CV3球粒陨石Efremovka，Kaba和Vigarano以及LL3.0球粒陨石Semarkona的七个尖晶石富集的细CAI，这两个已知具有挥发分馏的II组REE模式（可能是冷凝物）和另外三个可能是第II组，所有这些都使初始²⁶ Al / ²⁷ Al（²⁶ Al / ²⁷ Al ₀）接近于太阳系初始值5.2×10 ^–5。因此，我们的数据无法提供早期太阳系中多次凝结事件的证据。牛久保等人的其他著作。（2017）和Kawasaki等。（2019a，2019b）确实发现了一些相似的夹杂物，其值显着低于太阳系初始值。由于后面的数据太少，无法显示较低比率是否聚集或分布在某个范围内，因此需要进行更多工作来确定是否仅在几次严重的，破裂的热事件之后发生了星状凝露，或者更频繁地发生了。无论如何，现在已经很清楚，具有II类REE模式的CAI在太阳系历史中很早就形成了，与具有普通REE模式的CAI形成同时。不管形成第二组的机制是什么，它发生的条件是使尖晶石在陨石形成之前（比温度更高）冷凝。这与平衡星云凝结的预测相反。