Lithium concentrations and isotopic compositions of chondrules − Part I: Type I and type II chondrule systematics

We report high-precision lithium (Li) abundances and isotopic compositions of olivine crystals from type I chondrules in carbonaceous chondrites (Murchison, NWA 852, Renazzo) and type II chondrules in ordinary chondrites (NWA 11752, NWA 12462, NWA 12581, NWA 13501). Olivine crystals in type I chondrules exhibit large Li isotopic fractionations both within and between grains, with δ 7 Li values ranging from −46.6‰ to + 9.9‰ and Li concentrations of 3.8–9.0 ppm. Olivine grains in type II chondrules, including Mg-rich relict cores, show δ 7 Li values from −38.0‰ to + 8.4‰ (Li = 0.6–5.6 ppm), while their Fe-rich overgrowths exhibit lower variability, with δ 7 Li values between −30.6‰ and + 4.7‰ (Li = 0.6–11.9 ppm). Our data indicate that the observed variations are not attributable to low-temperature aqueous alteration or dry thermal metamorphism, fractional crystallisation, or simple degassing of the chondrule melt. Instead, the Li isotopic signatures are best explained by kinetic fractionation during open-system gas–melt exchange with a volatile-rich vapour, enriching the chondrule melts in Li. Such open-system processes produced larger isotopic fractionations than expected during closed-system crystallisation. These findings suggest that some type II chondrules may have originated from type I chondrules through reprocessing in an open-system environment, providing new insights into the complex physicochemical evolution of early solar system solids.