Abstract We report on the investigation of presolar grains and organic matter (OM) in 14 xenolithic carbonaceous clasts (C-clasts) identified in the Kapoeta howardite based on high-resolution NanoSIMS hydrogen, carbon, nitrogen, and oxygen isotopic imaging data. The 14 C-clasts are ∼50–200 μm in size and consist of one CM-like and 13 CI-like clasts, which are classified based on their mineralogies. The clasts from this study are likely sourced from an ice-bearing parent body, either an icy asteroid or a comet, originating from the outer solar system according to the following mineralogical observations: (1) in two CI-like clasts, embayments of magnetite grains between the C-clast and the host howardite point to aqueous alteration occurring on Vesta as a result of melting the ice embedded in the C-clasts; (2) all of the C-clasts, especially the 13 CI-like clasts, likely originated from the same parent body, because (i) the 14 C-clasts are clustered in the thin section, and (ii) the clasts show a much higher ratio of CI-like to CM-like clasts with respect to those reported in the literature. Four presolar silicon carbide (SiC) and two presolar silicate grains were identified in the C-clasts. In addition, all the C-clasts contain moderate bulk D- and 15N-enrichments with the presence of sub-micron to micron-sized D and 15N hotspots, indicating the presence of primitive organic material. Comparison of the abundances and isotopic compositions of presolar grains and OM in these C-clasts with literature data for different samples of primitive extraterrestrial material provides support for (1) the genetic linkage of xenolithic C-clasts to highly aqueously altered but minimally heated carbonaceous chondritic materials and (2) a homogeneous distribution of circumstellar and interstellar materials in the protoplanetary disk. The low amounts of heat experienced by the C-clasts suggest that they arrived at Vesta and/or Vestoids at low speeds after the late heavy bombardment in the inner solar system ∼3.5–4.0 Gyr ago.

中文翻译：

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来自 kapoeta Howardite 的捕集碳质碎屑的 NanoSIMS 同位素研究

摘要 我们报告了基于高分辨率 NanoSIMS 氢、碳、氮和氧同位素成像数据在 Kapoeta Howardite 中鉴定的 14 种捕集碳质碎屑 (C-clasts) 中的前太阳颗粒和有机质 (OM) 的研究。14 个 C 碎屑大小约为 50-200 μm，由 1 个类 CM 碎屑和 13 个类 CI 碎屑组成，根据其矿物学分类。根据以下矿物学观察，这项研究中的碎屑很可能来自含冰的母体，无论是冰冷的小行星还是彗星，根据以下矿物学观察结果：(1) 在两个类 CI 碎屑中，磁铁矿的海湾C-clast 和宿主霍华德石之间的颗粒表明，由于嵌入 C-clast 中的冰融化，灶神星上发生了水蚀；(2) 所有的 C-clast，特别是 13 个类 CI 碎屑，可能起源于同一母体，因为 (i) 14 个 C-碎屑聚集在薄片中，(ii) 类碎屑显示出更高的 CI 类碎屑与 CM-就像文献中报道的那些碎屑一样。在 C 碎屑中发现了四个太阳前碳化硅 (SiC) 和两个太阳前硅酸盐颗粒。此外，所有 C 碎屑都含有中等体积的 D-和 15N-富集，存在亚微米到微米大小的 D 和 15N 热点，表明存在原始有机材料。将这些 C-碎屑中的前太阳颗粒和 OM 的丰度和同位素组成与原始外星物质不同样本的文献数据进行比较，为 (1) 捕食 C-碎屑与高度含水改变但加热程度最低的碳质球粒陨石的遗传联系提供了支持(2) 原行星盘中星周和星际物质的均匀分布。C-clasts 所经历的少量热量表明它们在大约 3.5-4.0 Gyr 之前对太阳系内部的晚期重轰击之后以低速到达灶神星和/或 Vestoids。