Abstract We determined the silicon isotopic compositions of silicates (olivine and low-Ca pyroxene) in type I and type II chondrules of the carbonaceous chondrites Allende, Kaba, NWA (Northwest Africa) 5958, and MIL (Miller Range) 07342. Type I chondrule silicates show large, mass-dependent Si isotopic fractionations, with δ 30 Si values ranging from −7‰ to +2.6‰, whereas the δ 30 Si values of type II chondrule silicates are close to zero and vary by less than 2‰. When present, Mg-rich relict olivine grains in type II chondrules show larger Si variations than their FeO-rich counterparts. In type I chondrules, low-Ca pyroxenes yield systematically lighter δ 30 Si values than Mg-rich olivines. Our results show that type I chondrules are complex objects whose Si isotopic compositions derived from their precursors and SiO-rich gas-melt interactions. This corroborates that type I chondrules are nebular products that formed under open-system conditions. Our data also suggest that at least some type II chondrules derived from their type I counterparts. Overall, this demonstrates that recycling was common during the evolution of the protoplanetary disk.

中文翻译：

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碳质球粒陨石中球粒硅酸盐的硅同位素组成和吸积盘中原始固体的形成

摘要 我们确定了碳质球粒陨石 Allende, Kaba, NWA (Northwest Africa) 5958 和 MIL (Miller Range) 07342 的 I 型和 II 型球粒中硅酸盐（橄榄石和低钙辉石）的硅同位素组成。 I 型球粒硅酸盐显示出大的、质量相关的 Si 同位素分馏，δ 30 Si 值范围从 -7‰ 到 +2.6‰，而 II 型球粒硅酸盐的 δ 30 Si 值接近于零并且变化小于 2‰。当存在时，II 型球粒中富含 Mg 的残存橄榄石颗粒显示出比其富含 FeO 的对应物更大的 Si 变化。在 I 型球粒中，低 Ca 辉石比富含镁的橄榄石产生系统性更轻的 δ 30 Si 值。我们的研究结果表明，I 型球粒是复杂的物体，其 Si 同位素组成源自其前体和富含 SiO 的气体-熔体相互作用。这证实了 I 型球粒是在开放系统条件下形成的星云产物。我们的数据还表明，至少有一些 II 型球粒来自它们的 I 型对应物。总的来说，这表明在原行星盘的演化过程中回收是很常见的。