Abstract
China's Chang'E-5 mission returned new samples from the Moon and has extended the eruption ages of lunar volcanism ca. 800 million years younger than previous determinations. This finding challenges our past perceptions of the lunar thermal and magmatic evolution and has attracted great attention. Since the lunar basalts show a wide compositional range, it is essential to classify them carefully in order to define their origin and evolution. However, whether the Chang'E-5 basalts are classified as high-Ti or low-Ti type remains debatable because the basalt clasts picked from the Chang'E-5 soil samples are so tiny that tiieir bulk composition estimations involve large uncertainties. Instead of using bulk composition, this study employs Ti in olivine to track the crystallization sequence of the Chang'E-5 basalts and then to classify them. In the Chang'E-5 olivines, Ti contents first increase and then decrease with a continuous decrease of forsterite values. Such a compositional variation reveals a magma differentiation series from early ilmenite unsaturation to ilmenite saturation during the late stage. Furthermore, the TiO2 content of the hypothesized parental magma that corresponds to the most primitive olivine is estimated to be —4.4 wt%. These results confirm that the Chang'E-5 basalts originated from a low-Ti primary magma. This study shows that olivine can be used as a robust mineral indicator to distinguish between high-Ti and low-Ti mare basalts.
NSTL