We measured noble gases in “cluster chondrite clasts” from nine unequilibrated ordinary chondrites (UOCs). For five meteorites, we also present data for so‐called “clastic matrix,” the impact‐brecciated material in which the angular to subrounded cluster chondrite clasts are often embedded. Cluster chondrite clasts are characterized by close‐fit texture of deformed and indented chondrules with lower amounts of fine‐grained interchondrule matrix than in other UOCs (Metzler 2012). They are ubiquitous in UOCs and may indicate accretion and compaction of hot and deformable chondrules within hours or days after formation. Clastic matrix of four of the five meteorites contains He and Ne implanted by the solar wind (SW), indicating that they are regolith breccias. In contrast, cluster chondrite clasts are essentially devoid of SW, confirming that they are fragments of “primary accretionary rocks” (Metzler 2012). Trapped Kr and Xe in all samples are essentially primordial (type “Q”). Trapped Xe concentrations in cluster chondrite clasts are similar to values in other UOCs of similar metamorphic grade despite their low fractions of primordial gas‐bearing fine‐grained materials. This possibly indicates that the interchondrule matrix in cluster chondrite clasts is more pristine than matrix of regular UOCs. Later loss of primordial gases during parent body metamorphism is mirrored in the decreasing concentrations of primordial noble gases with increasing petrologic type. Relative to cluster chondrite lithologies, clastic matrix often contains excesses of cosmogenic noble gases, most likely due to precompaction exposure in the parent body regolith.

中文翻译：

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簇状球粒陨石碎屑及其宿主角砾岩中的稀有气体


我们测量了来自九个不平衡的普通球粒陨石（UOC）的“簇状球粒陨石碎屑”中的稀有气体。对于五颗陨石，我们还提供了所谓的“碎屑基质”的数据，即撞击角砾状材料，其中通常嵌入有角至近圆形的簇状球粒陨石碎屑。簇状球粒陨石碎屑的特征是变形和锯齿状球粒的紧密配合纹理，与其他 UOC 相比，细粒球粒间基质的数量较少（Metzler 2012）。它们在 UOC 中无处不在，可能表明热且可变形的球粒在形成后数小时或数天内发生吸积和压实。 5块陨石中的4块碎屑基质含有由太阳风（SW）注入的He和Ne，表明它们是风化角砾岩。相比之下，簇状球粒陨石碎屑基本上不含 SW，证实它们是“原生增生岩”的碎片（Metzler 2012）。所有样品中捕获的 Kr 和 Xe 本质上都是原始的（“Q”型）。簇状球粒陨石碎屑中捕获的 Xe 浓度与类似变质等级的其他 UOC 中的值相似，尽管它们的原始含气细粒材料比例较低。这可能表明簇状球粒陨石碎屑中的球粒间矩阵比规则 UOC 的矩阵更原始。母体变质作用过程中原始气体的后期损失反映在原始稀有气体浓度随着岩石类型的增加而降低。相对于簇状球粒陨石岩性，碎屑基质通常含有过量的宇宙成因惰性气体，很可能是由于母体风化层中的预压实暴露所致。