Primitive meteorite groups such as the Vigarano, Mighei, and Karoonda carbonaceous chondrites have enigmatic patterns of elemental abundances, with moderately volatile elements—those that transition from vapor to condensate between ∼400 and ∼900 K—defining plateaus of subequal abundances despite a wide range in volatility. In detail, each group defines a plateau with distinctive nonmonotonic “chemical fingerprints” that have been attributed to combinations of mixing, vaporization/condensation, and fluid-mediated metasomatism—but the extent to which these processes can reproduce the observed variability has not been quantified. Starting with primitive Ivuna chondrite, a two-stage, two-component equilibrium condensation–vaporization model—with gravity implemented as Jeans escape—can explain large-scale plateaus in these chondrite groups, as well as more complex, nonmonotonic small-scale variations. For all three chondritic meteorite groups, models favor earlier high-temperature fractionation under low-gravity conditions followed by a low-temperature fractionation event that took place on a protoplanet at least as large as Ceres. The second fractionation event may represent the fractionation of incoming materials to the planetesimal during protracted pebble accretion. Models with only thermally driven volatile loss, gravity, and mixing can explain more than 80% of the observed compositional variability in these meteorite groups. In our five-parameter model, using only five randomly selected elements yields uselessly large ranges of planet sizes and temperatures, ranges that converge with increasing numbers of elements. These results suggest that even simple models are prone to generating inaccurate conclusions when constrained by too few observations, a fault likely held by more complex models as well.

中文翻译：

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丰度-挥发性模型有利于大型碳质球粒陨石母体：卵石增生的可能化学特征

原始陨石群，如 Vigarano、Mighei 和 Karoonda 碳质球粒陨石，具有神秘的元素丰度模式，其中有中等挥发性的元素（这些元素在 ~400 至 ∼900 K 之间从蒸气转变为冷凝物），尽管范围很广，但定义了丰度接近相等的平台。在波动性中。详细地说，每个组都定义了一个具有独特的非单调“化学指纹”的平台，这些“化学指纹”归因于混合、蒸发/冷凝和流体介导的交代作用的组合，但这些过程可以在多大程度上重现观察到的变异性尚未量化。从原始的伊武纳球粒陨石开始，一个两阶段、两组分的平衡凝结-蒸发模型——重力以牛仔裤逃逸的形式实现——可以解释这些球粒陨石群中的大尺度高原，以及更复杂、非单调的小尺度变化。对于所有三个球粒陨石群，模型倾向于在低重力条件下早期发生高温分馏，随后在至少与谷神星一样大的原行星上发生低温分馏事件。第二次分馏事件可能代表在延长的卵石吸积过程中进入的物质分馏为星子。仅由热驱动的挥发性损失、重力和混合的模型可以解释这些陨石群中观察到的 80% 以上的成分变化。在我们的五参数模型中，仅使用五个随机选择的元素会产生无用的大范围的行星大小和温度，这些范围随着元素数量的增加而收敛。这些结果表明，即使是简单的模型，当受到观测值太少的限制时，也容易产生不准确的结论，更复杂的模型也可能存在这种错误。