Timing and characteristics of the latest mare eruption on the Moon

Unraveling the timing and duration of mare volcanism on the Moon is essential for understanding its thermal evolution. The end of mare volcanism is poorly constrained, because mare basalts are incompletely sampled. In this study, employing SELENE (Kaguya) high-resolution images, we performed new crater size-frequency measurements for 49 young mare units (<~3.0 Ga) in the Procellarum KREEP Terrane (PKT), in which the latest magma eruption of the Moon occurred. Mare volcanism in this region continued until ~ 1.5 Ga, suggesting that volcanic activity in this region ceased ~ 1.0 Ga after the magma eruption had globally ceased 2.5–3.0 Ga. Volcanic activity may have peaked 1.8–2.2 Ga ago. The youngest basalts occur around the Aristarchus plateau and the Kepler crater, which are located in the central region of the PKT. It is likely that heating in the crust due to the concentration of heat-producing elements in the PKT delayed cooling of a partial-melting zone in the underlying mantle. In contrast with previous basalt dating in this region, our results indicate a higher correlation between ages and spectral types of mare basalts; the young mare units in the PKT tend to have spectral types corresponding to high titanium contents, while low titanium basalts occur mainly in the early stage. The titanium variation in mare basalts may reflect vertical heterogeneity in TiO2 content in the upper mantle beneath the PKT.