Institut de Physique du Globe de Paris, Université de Paris, CNRS UMR 7154, 75238 Paris, France;
Institut de Physique du Globe de Paris, Université de Paris, CNRS UMR 7154, 75238 Paris, France.
Proc Natl Acad Sci U S A. 2019 Sep 17;116(38):18860-18866. doi: 10.1073/pnas.1907592116. Epub 2019 Sep 4.
The so far unique role of our Solar System in the universe regarding its capacity for life raises fundamental questions about its formation history relative to exoplanetary systems. Central in this research is the accretion of asteroids and planets from a gas-rich circumstellar disk and the final distribution of their mass around the Sun. The key building blocks of the planets may be represented by chondrules, the main constituents of chondritic meteorites, which in turn are primitive fragments of planetary bodies. Chondrule formation mechanisms, as well as their subsequent storage and transport in the disk, are still poorly understood, and their origin and evolution can be probed through their link (i.e., complementary or noncomplementary) to fine-grained dust (matrix) that accreted together with chondrules. Here, we investigate the apparent chondrule-matrix complementarity by analyzing major, minor, and trace element compositions of chondrules and matrix in altered and relatively unaltered CV, CM, and CR (Vigarano-type, Mighei-type, and Renazzo-type) chondrites. We show that matrices of the most unaltered CM and CV chondrites are overall CI-like (Ivuna-type) (similar to solar composition) and do not reflect any volatile enrichment or elemental patterns complementary to chondrules, the exception being their Fe/Mg ratios. We propose to unify these contradictory data by invoking a chondrule formation model in which CI-like dust accreted to so-called armored chondrules, which are ubiquitous in many chondrites. Metal rims expelled during chondrule formation, but still attached to their host chondrule, interacted with the accreted matrix, thereby enriching the matrix in siderophile elements and generating an apparent complementarity.
迄今为止，我们的太阳系在其生命能力方面在宇宙中具有独特的地位，这就提出了关于其形成历史相对于系外行星系统的基本问题。在这项研究中，核心问题是富气的原行星盘内小行星和行星的吸积以及它们在太阳周围的最终质量分布。行星的关键组成部分可能由球粒代表，球粒是球粒陨石的主要成分，而球粒陨石又是行星体的原始碎片。球粒形成机制及其在盘中的后续储存和运输仍然知之甚少，它们的起源和演化可以通过它们与细粒尘埃（基质）的联系（即互补或非互补）来探测，这些细粒尘埃与球粒一起吸积。在这里，我们通过分析改变和相对未改变的 CV、CM 和 CR（Vigarano 型、Mighei 型和 Renazzo 型）球粒陨石中的球粒和基质的主要、次要和微量元素组成来研究明显的球粒-基质互补性。我们表明，最未改变的 CM 和 CV 球粒陨石的基质总体上类似于 CI（Ivuna 型）（类似于太阳成分），并且不反映任何挥发性富集或与球粒互补的元素模式，例外是它们的 Fe/Mg 比。我们建议通过调用一个球粒形成模型来统一这些矛盾的数据，在该模型中，CI 样尘埃吸积到所谓的装甲球粒上，而装甲球粒在许多球粒陨石中普遍存在。球粒形成过程中喷出的金属边缘仍附着在其母体球粒上，与吸积的基质相互作用，从而使基质富含亲铁元素，并产生明显的互补性。
