Distribution analysis of rare earth elements in fine-grained CAIs of the Allende meteorite using multiple-spot femtosecond LA-ICP-MS

Calcium–aluminum-rich inclusions (CAIs) in chondrites are one of the oldest materials in the solar system. Presence of refractory minerals in CAIs suggests that they formed thorough a condensation process from nebular gas of solar composition. In particular, fine-grained CAIs (FGs) have escaped melting after condensation, and thus, the elemental distribution of rare earth elements (REEs) in FG minerals provides key information for elucidating the condensation processes. Although the REE abundances of FG fragments have been investigated in previous studies, the distribution of REEs in individual FG constituent minerals remains poorly explored. Here, we demonstrate the utility of laser imaging of REE distribution in CAIs by analyzing five FGs found in the Allende CV3 chondrite using multiple-spot femtosecond laser ablation (msfsLA)-ICP-MS. The msfsLA-ICP-MS imaging system allows for a rapid acquisition of a wider range of REE distributions than previously achieved by Secondary ion mass spectrometry-based imaging techniques. Out of the five FGs examined in this study, three showed the homogeneous REE patterns, while the other two indicated variable REE patterns within each FG. These observations presumably reflect differences in the chemical processes experienced by the FGs, and indicate that multi-step chemical processes were recorded in some of the FGs. The msfsLA-ICP-MS imaging technique can characterize the elemental distribution of individual FGs under the comparable spatial resolution with high-analysis throughput, and thus, it is an effective new method for advancing the taxonomy of FGs, which will improve our understanding of the physicochemical conditions that prevailed in the early solar system.