Formation of the young (< 3 Ga) lunar volcanism: Insight from Chang’e-6 samples

The return of the Chang’e samples has confirmed that lunar volcanic activities remained active after the Imbrian-aged eruptions, yet the thermodynamic mechanisms driving these young volcanic events remain unresolved. The basalts retrieved by Chang’e-6 (CE-6) originated from young volcanism on the far side of the Moon, and the comparison of them with young near side basalts can provide new insights into the thermal evolution of the lunar interior. Researchers conducted systematic petrological, mineralogical, and isotopic analyses on the CE-6 basalts, identifying two distinct types of mare basalts: low-Ti basalts (~2.8 Ga) and ultra-low-Ti basalts (~2.9 Ga). Trace elements and phase equilibrium models show that their source regions are ilmenite-bearing pyroxenites at a depth of about 60–80 km and clinopyroxene-rich cumulates at a depth of about 120 km, respectively. The variation in source depth indicates that the thermal triggering mechanism is bottom-up rather than top-down. Numerical simulations suggest that magmatic underplating between the shallow pyroxenite cumulates and the underlying peridotites may be the primary thermal mechanism of the young volcanism. Global remote-sensing investigations further support this model and reveal differences in the chemical features of young basalts from both sides of the Moon: the near side is dominated by intermediate-Ti basalts similar to Chang’e-5 basalts, whereas the far side is characterized by VLT basalts similar to those from CE-6. This disparity reflects the asymmetry in the composition and structure of the lunar mantle, providing important constraints on the origin of the lunar dichotomy.