Sulfur isotopes from the lunar farside reveal global volatile loss following the giant impact.

Abstract

The Moon is strongly depleted in volatile elements and exhibits heavier isotopic signatures (e.g., K, Zn) than the Earth. However, the pronounced nearside-farside dichotomy and uneven distribution of volatiles across lunar interior raise the question of whether such heavier isotopic signatures resulted from a global giant impact or local magmatic processes. Here we report high sulfur contents (1800 ± 400 µg/g) and δ³⁴S values (0.83 ± 0.16‰, 2SE, n = 17) in Chang'e-6 basalt from lunar farside, with similar δ³⁴S values in two nonmare crustal clasts. These values fall within the range reported for nearside mare basalts and basaltic meteorites of different ages and mantle sources, indicating a broadly homogeneous δ³⁴S composition across lunar interior that is ~2‰ heavier than the Earth's mantle. This isotopic signature cannot be explained by core formation or late accretion and is best attributed to global volatile loss during the Moon-forming impact. Subsequent magma ocean evolution and mantle overturn drove heterogeneous volatile budget in lunar mantle.