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富铝球粒(ARC)在岩矿学和同位素组成等方面兼具富钙富铝难熔包体(CAI)和镁铁质球粒的特征,可以揭示其成因及时空关系因而成为天体化学重要的研究对象之一.本文研究了3个普通球粒陨石(GRV 022410(H4),GRV 052722(H3.7)和Julesburg(L3.6))中发现的7个富铝球粒.详细的岩相学和矿物学研究表明,这些富铝球粒的全岩Al2O3含量为17%~33%,均显示火成结构,主要由橄榄石、高钙和低钙辉石、长石、尖晶石和玻璃组成.离子探针原位分析显示,富铝球粒组成相的氧同位素成分(δ18O=–6.1‰~7.1‰;δ17O=–4.5‰~5.1‰)与镁铁质球粒相近,远比CAI(δ18O=-40‰;δ17O=-40‰)亏损16O.在三氧同位素图上,大部分富铝球粒投在地球分异(TF)线附近,少部分(含尖晶石)投在TF线和碳质球粒陨石无水矿物(CCAM)线之间.长石、霞石及玻璃的氧同位素成分是母体变质过程中氧同位素交换的结果.尖晶石、橄榄石及辉石的氧同位素成分代表了原始的富铝球粒的氧同位素组成,这些数据拟合线的斜率为0.7±0.1.与前人研究结果相比,更缓的斜率及更贫16O的成分进一步表明普通球粒陨石中的富铝球粒不是CAI与镁铁质球粒简单混合形成的.相反,他们很有可能在多次熔融过程中与贫16O的星云气体储库经历了更高程度的氧同位素交换.
Aluminum-rich grains (ARC) have the characteristics of both calcium-rich aluminum-rich refractory inclusions (CAI) and mafic spherulites in terms of petrography and isotopic composition, revealing their genesis and spatiotemporal relationships and thus becoming astrophysical important .In this paper, we study seven aluminum-rich spherulites found in three common chondrules (GRV 022410 (H4), GRV 052722 (H3.7) and Julesburg (L3.6) Phylogeny and mineralogical studies have shown that the Al 2 O 3 pellets have a whole-rock Al2O3 content of 17% -33%, showing an eruptive structure mainly composed of olivine, high-calcium and hepasite, feldspar, spinel and Glass composition.The ion probe in-situ analysis showed that the oxygen isotopic composition (δ18O = -6.1 ‰ ~ 7.1 ‰; δ17O = -4.5 ‰ ~ 5.1 ‰) of the Al-rich pellets was similar to that of the mafic pellets On the oxygen isotope chart, most of the aluminum-rich spherulites are cast near the TF (TF) line, and a small proportion (including spinel) is cast on the CAI (δ18O = -40 ‰; δ17O = -40 ‰) Between the TF line and the CCAM line, the oxygen isotopic composition of feldspar, nepheline, and glass is the result of oxygen isotope exchange during maternal metamorphism. The spinel, olivine and pyroxene The isotopic composition represents the oxygen isotopic composition of the original aluminum-rich spherulites, and the slopes for these data fitting lines are 0.7 ± 0.1. The slower slope and the poorer 16O components compared to previous studies further demonstrate that common pellets Aluminum-rich pellets in meteorites are not formed by simple mixing of CAI with malleable pellets, but rather, they are likely to undergo a higher degree of oxygen isotope exchange with the 16.0-depleted nebular gas reservoir over multiple fusions.