A Reassessment of the Lithium Isotope Composition of the Moon Using Mare Basalt, Mg‐Suite and Anorthosite Meteorites

Abstract

To further constrain the lunar Li isotopic composition and its behavior during lunar magmatic differentiation, we measured twelve lunar meteorites, including mare basalts, Mg‐suite rocks and anorthosites. Petrographic observation, dilute acid cleaning, and trace elemental characteristics indicate minimal terrestrial contamination. Low‐Ti basalt meteorites yield a restricted δ ⁷ Li range (2.75 ± 0.52‰ to 3.95 ± 0.16‰), consistent with Apollo low‐Ti basalts (3.1∼5.6‰). The Mg‐rich norite Arguin 002 shows a similar value, supporting limited Li isotope fractionation during early lunar magma ocean (LMO) differentiation, a conclusion corroborated by modeling results of Li isotopic evolution during LMO differentiation. The heavier δ ⁷ Li in high‐Ti basalts, however, points to the presence of interaction between ilmenite‐bearing cumulate‐derived melts and the ambient mantle rather than to simple late‐stage LMO differentiation. Combining the reported Apollo and La Paz mare basalt meteorites data, we estimate the lunar mantle δ ⁷ Li to be 3.8 ± 1.3‰, indistinguishable from the Earth's mantle, implying negligible fractionation during the Giant Impact. In contrast, lunar anorthosites exhibit extreme δ ⁷ Li variations (−0.7‰ to 9.8‰) with a negative correlation with Li content, likely reflecting impact‐driven secondary redistribution. These findings not only confirm the Earth‐Moon Li isotopic similarity using meteorites from diverse lunar terrains that complement the Apollo collection but also reveal that the lunar crust has been pervasively modified by impact processes, which have significantly disturbed its primary Li isotopic compositions.