Petrogenesis of Chang’e-6 Basalts and Implication for the Young Volcanism on the Lunar Farside

Abstract

Mare basalts from lunar farside are pivotal for unraveling lunar nearside-farside dichotomies and global thermal history. The Chang’e-6 (CE-6) mission conducted the first sampling from a young basaltic unit within the Apollo basin on the lunar farside. Here, we performed comprehensive petrological and geochemical analyses on the CE-6 basalt clasts. The CE-6 basalt is a low-titanium basalt (about 5 wt% TiO2) depleted in KREEP components. The absence of olivine, particularly magnesium-rich olivine, suggests that the basaltic magma underwent extensive fractional crystallization. Thermodynamic modeling supports that there may be 10%–20% late-stage cumulates of magma ocean (clinopyroxene and ilmenite) present in the source region of CE-6 basalt. The magma derived from the partial melting of such lunar mantle may undergo fractional crystallization dominated by olivine and clinopyroxene within a shallow magma cg1hamber, followed by eruption. Modeling of the REE pattern further indicates that 3%–7% batch melting of a depleted lunar mantle source, combined with 21%–59% fractional crystallization, achieves the observed REE abundances of CE-6 basalt. The genesis of CE-6 basalt could be attributed to the synergistic influence of a readily fusible mantle source, resulting from the incorporation of late-stage cumulates, and the crust-mantle deformation induced by large impacts. This could serve as a paradigm for the formation of other young basalts on the Moon.