Chemical and isotopic compositions of aluminum-rich chondrules: insights into material mixing in the early solar systemOPEN ACCESS
Yuki Masuda, Yoshiaki Shiraishi, Tetsuya Yokoyama, Tsuyoshi Iizuka, Martin Schiller, Martin Bizzarro
Geochimica et Cosmochimica Acta
In Press, Journal Pre-proof, Available online 5 July 2026
“Chondrules are high-temperature products formed in the protoplanetary disk and are ubiquitous components of undifferentiated extraterrestrial materials. Nucleosynthetic isotope anomalies preserved in chondrules provide a valuable record of isotopic evolution of solids from presolar dust to the accretion of planets. Among various types of chondrules, Al-rich chondrules (ARCs) possess intermediate isotopic and chemical compositions between calcium-aluminum-rich inclusions (CAIs) and ferromagnesian chondrules (FMCs), providing insights into mixing processes of various materials formed in different regions and/or at different times in the protoplanetary disk. This study performed analyses of the abundances of 54 elements and multi-elemental isotopic compositions of Ca-Ti-Cr-Sr on fourteen ARCs extracted from four Vigarano-type chondrites (CVs). Their element abundance patterns demonstrate enrichments reaching up to 10 times of Ivuna-type carbonaceous chondrites (CIs) in refractory elements and depletions down to < 0.05 × CI in volatile elements. Eight ARCs show highly fractionated rare-earth-elements (REEs) signatures, while six ARCs display flat REE patterns. These features suggest that CV ARCs have recycled refractory inclusions, including fine-grained CAIs (FG-CAIs) and other REE-unfractionated types, in addition to less-refractory components with chondritic or matrix-like compositions similar to those contributing to FMCs. The Ca, Ti, and Sr isotopic compositions of the ARCs exhibit variations ranging from those of non-carbonaceous chondrite (NC) components to coarse-grained CAIs (CG-CAIs) and FG-CAIs. The observed isotopic compositions are not consistent with a simple mixture of NC with a single type of refractory inclusion, suggesting that they contain various types of refractory materials. The Cr isotopic compositions of CV ARCs are intermediate between those of NCs and CIs. The observed isotopic variation indicates that components of NC, CI, and refractory inclusions coexisted in the CV chondrule-forming region. This is in contrast to NC chondrule-forming regions, which do not exhibit isotopic anomalies characteristic of refractory inclusions. The significant difference in the degree of CAI signatures between OC ARCs and CV ARCs suggests that CAIs were trapped between the accretion regions of NC and CC parent bodies, leading to an isotopic dichotomy based on the presence or absence of isotopically anomalous CAIs. Meanwhile, fine dust grains with NC or CI isotopic compositions, which are smaller in size than CAIs, were distributed extensively in NC and CC accretion regions, resulting in continuous variations in chondrule isotopic composition.”
