Petrologic evidence for core sulfur degassing in partially differentiated planetesimals

Partial differentiation hypothesis is a scenario for interpreting the internal structure of planetesimals and the genetic relationship between chondrites and nonchondrites. However, no petrologic records supporting this hypothesis have been reported yet. Here, we report sulfide replacement textures of melilite and olivine in Ornans-like chondrites, whose occurrences are correlated with the degree of thermal metamorphism of the host chondrites. The mineral assemblages of the replacement textures and the correlation with petrologic subtype are best explained with high-temperature reactions between silicate phases and S-rich vapors, which degassed from a solidifying Fe-Ni-S core. The sulfide replacement texture in Ornans-like chondrites could be the first petrologic record supporting the partial differentiation hypothesis. Given the widespread presence of sulfide replacement textures in different meteorites, we propose that core sulfur degassing could be an endemic process in differentiated planetesimals.