Leaching-induced Li isotope variations in weathered ordinary chondrites: Implications for terrestrial alteration

Abstract

Meteorite finds are commonly used to assess the chemical and isotopic compositions of their parent bodies. Among these, lithium (Li) isotopes in ordinary chondrites (OCs) have been applied to infer the Li abundance and isotopic characteristics of their parent bodies. However, Li is highly mobile in aqueous conditions and readily undergoes isotopic fractionation during fluid–mineral interactions. It remains uncertain whether Li isotopic compositions in meteorite finds reliably preserve their original parent-body signatures, particularly after prolonged terrestrial exposure. In this study, we investigated Li isotope behavior in Kumtag 015 (W3, L5) by conducting a series of leaching experiments. The untreated whole-rock sample yields a δ⁷Li value of +6.1‰, whereas all leachates exhibit heavier δ⁷Li values, ranging from +8.4‰ to +14.8‰, indicating the presence of weathering-related secondary components enriched in heavy Li isotopes. Combined with the petrographic observations and mass-balance results, these data suggest that the relatively heavy whole-rock δ⁷Li of Kumtag 015 is mainly related to the addition of heavy-δ⁷Li surficial fluids during terrestrial weathering, followed by the sequestration of Li into secondary minerals such as carbonates and Fe-(oxyhydr)oxides. This finding is consistent with prior work showing heavy δ⁷Li in carbonates. We conclude that terrestrial alteration can substantially modify Li isotope compositions in meteorite finds, highlighting the need for caution when using such samples to trace pristine planetary Li inventories.