Sorting and recycling processes of early inner Solar System materials

Within pristine chondrites, chondrules and a fine-grained matrix are the dominant components; however, their genetic relationship remains unresolved. Specifically, during chondrule formation through multiple heating events, recycling of chondritic materials was inevitable, yet its influence on elemental distributions between chondrules and the residual material that ultimately became the matrix remains poorly understood. We aim to evaluate how recycling processes influence the chemical relationship between chondrules and matrix in unequilibrated ordinary chondrites and the parent body evolution. We performed systematic major and trace element analyses of silicate minerals, chondrule mesostasis, and matrix in nine unequilibrated ordinary chondrites using an in situ analytical technique, combined with numerical simulations to model recycling processes and parent body evolution. Our analytical results show that chondrule mesostasis exhibits the lowest Mg/Si ratios, followed by the matrix and chondrule silicates. Both mesostasis and matrix display similar enrichment patterns in incompatible elements, although matrix compositions vary widely among samples. These observations suggest that recycling was accompanied by compositional sorting, leading to differential reincorporation of mesostasis- and silicate-derived fragments. Numerical simulations further reproduce (1) the chemical divergence between chondrules and matrix, (2) variable enrichment of incompatible elements in the matrix, and (3) heavy-isotope enrichment of moderately volatile elements. In addition, sorting during accretion likely resulted in variable Al abundances among chondrite parent bodies, thereby influencing the duration and extent of their thermal evolution. Early-stage recycling coupled with compositional sorting played a key role in establishing the chemical diversity of materials accreting to planetesimals and exerted a fundamental control on their thermal evolution in the early Solar System.