Petrogenesis of Chang'E-6 basalts and implication for multi-episode volcanism in the lunar farside basin

Abstract

Mare basalts are products of lunar mantle via partial melting, and hence viewed as crucial probes of the mantle's composition and thermal state. While previous mission-returned lunar samples have provided valuable insights into the composition and structure of the lunar interior, our understanding remains limited because all samples have been collected from the lunar nearside. Consequently, numerous scientific questions about the Moon's dichotomy remain unresolved. In June 2024, China's Chang'E-6 (CE-6) mission successfully returned the first-ever samples from lunar farside, which marks a new era in lunar science. In this work, we examine the petrography, mineralogy, and geochemistry of CE-6 basaltic fragments. Our results reveal that the basaltic fragments at the CE-6 landing site exhibit variable chemical compositions, ranging from very low-Ti to low-Ti types. The diversity in the petrogenesis of these basaltic rocks demonstrates significant differences in the mantle source and subsequent magmatic processes. Combined with remote sensing data, these findings indicate a complex thermal evolution for the southern mare of the Apollo basin in the South Pole-Aitken (SPA) basin, which experienced at least three episodes of volcanism. Additionally, the broad variation in TiO₂ content suggests the possibility of even more episodes of volcanism occurred and more types of basalts existed in this farside basin of the Moon. Furthermore, the multi-episodes magmatism occurred in the lunar farside basin, suggests that spatial variations in magma production rates across the Moon's interior may be negligible. The petrogenetic modeling of CE-6 basaltic fragments demonstrates that incompatible element concentrations and mineral modes are likely to be similar across lunar nearside to farside mantle. In contrast, the lunar crust appears to play a critical role in controlling basaltic magma eruptions on the farside surface.