CI chondrites have nonvolatile chemical compositions closely resembling that of the Sun’s photosphere and are thus considered to have the most primitive compositions of all known solar system materials. They have, however, experienced pervasive parent-body alteration processes that transformed their primary constituents, obscuring the nature and origin of primordial CI dust. We used in-situ quantitative microprobe and secondary ion mass spectrometry techniques to characterize the chemistry and oxygen isotopic compositions of anhydrous silicates in two sections of the CI chondrites Ivuna and Alais, which contain higher abundances of those than other CI samples. These silicates are Mg-rich olivine and low-Ca pyroxene crystals mostly occurring as aggregates within sub-mm Fe-rich clasts. Our data reveal mass-independent oxygen isotopic variations with Δ¹⁷O values ranging from −23.63 to −0.57‰, representing the first evidence of extremely ¹⁶O-rich (Δ¹⁷O < −20‰) olivine and pyroxene grains in CI chondrites. Two of these olivines are characterized by MnO/FeO ∼ 1, typical of low-iron, Mn-enriched silicates commonly observed in amoeboid olivine aggregates. Other anhydrous silicate grains have Δ¹⁷O values ranging from −6 to 0‰, probably representing chondrule fragments. Combined, these results indicate that chondrule and refractory inclusion material were incorporated into the CI parent body(ies). This conclusion is consistent with recent models showing that refractory inclusions could have formed and/or been transported at larger heliocentric distances than previously thought during the concomitant injection of material from the molecular cloud and outward extension of the disk by viscous spreading. The CI chondrules are presumably of local origin, with their isotopic systematics suggesting an affinity with the CR clan.

CI球粒陨石具有与太阳光球层非常相似的非挥发性化学成分，因此被认为具有所有已知太阳系材料中最原始的成分。然而，它们经历了普遍的母体改变过程，改变了它们的主要成分，掩盖了原始 CI 尘埃的性质和起源。我们在现场使用定量微探针和二次离子质谱技术，用于表征 CI 球粒陨石 Ivuna 和 Alais 的两个部分中无水硅酸盐的化学和氧同位素组成，这两个部分的丰度高于其他 CI 样品。这些硅酸盐是富含镁的橄榄石和低钙辉石晶体，主要作为亚毫米富铁碎屑中的聚集体出现。我们的数据揭示了与质量无关的氧同位素变化，Δ ¹⁷ O 值范围从 -23.63 到 -0.57‰，代表了极富¹⁶ O（Δ ¹⁷O < -20‰) CI 球粒陨石中的橄榄石和辉石颗粒。其中两种橄榄石的特征是 MnO/FeO~1，这是在变形橄榄石聚集体中常见的低铁、富含 Mn 的硅酸盐的典型特征。其他无水硅酸盐颗粒有 Δ ¹⁷O 值范围从 -6 到 0‰，可能代表球粒碎片。综合起来，这些结果表明球粒和耐火夹杂物被掺入 CI 母体中。这一结论与最近的模型一致，该模型表明，在从分子云同时注入材料和通过粘性扩散向外延伸圆盘的过程中，难熔夹杂物可能已经形成和/或以比以前认为的更大的日心距离传输。CI 球粒可能起源于当地，它们的同位素系统表明与 CR 氏族有亲缘关系。