CM球粒陨石的原始三维化学成分揭示外盘中球粒的形成
Chondrule formation in the outer disk from the primary three-dimensional chemical composition of CM chondrules
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中文总结 AI 辅助
通过分析CM球粒陨石的66个球粒及细粒环边的元素组成与三维形态，提出外盘球粒形成的“微球粒优先”场景，揭示局域熔融与聚集的关键作用。
中文摘要 AI 辅助
球粒及其相关的细粒环边记录了原行星盘中的关键过程，但球粒的化学组成、形态与基质互补性之间的联系仍未得到充分约束。我们采用LA-ICP-MS与X射线断层扫描技术，对来自相对未受蚀变的CM型碳质球粒陨石Asuka 12236、Paris和Maribo的66个球粒及细粒环边（FGRs）的主量、微量与痕量元素组成，连同其三维形态展开研究。CM球粒记录了系统性的金属损失与富硅基质的蒸发，使初始类CI的前驱体组成沿CI比例线向更富镁、硅的整体组成转变，并形成日益贫硅的镁橄榄石集合体。原始CM基质中的类GEMS材料与球粒组成高度吻合，可能代表源自蒸发基质的互补冷凝物。附着在球粒上的尘埃主要为类CI成分，但包含约14 wt.%的互补冷凝物（由球粒状无定形硅酸盐代表），协调了球粒与基质间的Mg/Si互补性，同时保留了原始有机物与前太阳颗粒。形态观测显示无显著切片偏差，与CM球粒主要由~100 μm微球聚集体组成的结论一致，许多球粒呈现由较小球粒与富金属或类CI环边熔接形成的葡萄串状结构，该结构可解释球粒中等挥发性元素在约0.3×CI处的平台。我们提出“微球粒优先”场景：局域加热事件产生小型熔融液滴，随后附着类CI尘埃与冰、聚集并经历有限的水蚀变。这些观测为外盘中球粒的形成提供了新约束，并凸显了局域熔融与聚集过程的重要性。
英文摘要
Chondrules and their associated fine-grained rims record key processes in the early protoplanetary disk, yet the links between chondrule chemistry, morphology, and matrix complementarity remain poorly constrained. We investigate the major, minor, and trace element compositions of 66 chondrules and FGRs from the relatively unaltered CM carbonaceous chondrites Asuka 12236, Paris, and Maribo, together with their 3D morphology, using LA-ICP-MS and X-ray tomography. CM chondrules record systematic metal loss and evaporation of Si-rich mesostasis, driving initially CI-like precursor compositions toward more Mg- and Si-rich bulk compositions along the CI ratio line and toward increasingly Si-poor forsteritic assemblages. GEMS-like materials in pristine CM matrices closely mirror chondrule compositions and likely represent complementary condensates derived from evaporated mesostasis. Dust accreted onto chondrules is predominantly CI-like but contains about 14 wt.% complementary condensate material represented by chondritic amorphous silicates, reconciling Mg/Si complementarity between chondrules and matrix with the preservation of primordial organics and presolar grains. Morphological observations show no significant sectioning bias, consistent with CM chondrules being dominated by agglomerates of ~100 um microspherules. Many display grape-bunch textures produced by welding of smaller chondrules with metal-rich or CI-like rims. This structure may explain the chondrule moderately volatile-element plateau at about 0.3xCI. We propose a "micro-chondrule-first" scenario in which localized heating events produced small molten droplets that subsequently accreted CI-like dust and ice, aggregated, and experienced limited aqueous alteration. These observations place new constraints on chondrule formation in the outer disk and highlight the importance of localized melting and aggregation processes.
