Sulfur lsotope Effect and the Discovery of 120 Ma Volcanic Glasses in Chang'e-5 Samples

Lunar volcanic products are crucial for understanding the Moon’s formation and evolution. These samples not only record early lunar volcanic activity but also reveal the Moon’s internal structure and composition. In addition to igneous rocks, volcanic glasses can represent the lunar mantle. Eruptions of gas-rich magma can produce magma fountains, generating submillimeter glass beads that may be widely distributed and further transported by impacts. Such glasses could exist as trace components in lunar samples. Recent studies of hundreds of glass beads in Chang’e-5 samples found that three-fourths contain undigested clasts, indicating an impact origin. Glasses without clasts but with compositional heterogeneity are also classified as impact glasses, as their compositions often match the local regolith. For chemically homogeneous glasses free of mineral fragments, traditional major-element criteria are insufficient for classification.

Impact glasses exhibit diverse major- and trace-element compositions. Distinguishing volcanic glasses from abundant impact glasses in lunar regolith requires a multi-criteria approach. By analyzing textures, major and trace elements, and in-situ sulfur isotopes, three picritic volcanic glasses were identified among ~3,000 glasses in Chang’e-5 samples. This methodology can be applied to other lunar samples, providing data to assess the frequency of volcanic eruptions in lunar history.

Radiometric dating of the three Chang’e-5 volcanic glass beads confirms 120-million-year-old lunar volcanism, supporting remote sensing evidence of relatively young volcanic activity, such as Irregular Mare Patches (IMPs). These findings demonstrate that the Moon remained volcanically active until ~120 million years ago, offering new insights into its thermal and geological evolution.