A changing thermal regime revealed from shallow to deep basalt source melting in the Moon

Abstract

Sample return missions have provided the basis for understanding the thermochemical evolution of the Moon. Mare basalt sources are likely to have originated from partial melting of lunar magma ocean cumulates after solidification from an initially molten state. Some of the Apollo mare basalts show evidence for the presence in their source of a late-stage radiogenic heat-producing incompatible element-rich layer, known for its enrichment in potassium, rare-earth elements, and phosphorus (KREEP). Here we show the most depleted lunar meteorite, Asuka-881757, and associated mare basalts, represent ancient (~3.9 Ga) partial melts of KREEP-free Fe-rich mantle. Petrological modeling demonstrates that these basalts were generated at lower temperatures and shallower depths than typical Apollo mare basalts. Calculated mantle potential temperatures of these rocks suggest a relatively cooler mantle source and lower surface heat flow than those associated with later-erupted mare basalts, suggesting a fundamental shift in melting regime in the Moon from ~3.9 to ~3.3 Ga.

Petrogenesis of Chang'E‐5 young mare low‐Ti basalts

“…Therefore, the low degree assimilation of KREEP‐bearing basaltic fragments in lunar regolith cannot alter the isotopic signatures of CE‐5 basalts inherited from the mantle source (e.g., Li et al., 2021; Tian et al., 2021; Zong et al., 2022). This late KREEP assimilation process is consistent with that the radioactive heat generated by KREEP may not be the mechanism to account for young volcanism on the Moon (Srivastava et al., 2022; Su et al., 2022). KREEP might play only a minor role in both early (e.g., Gross et al., 2020; Prissel & Gross, 2020) and late lunar mantle melting.…”

Lithologies and Chronologic Opportunities of Materials to Be Returned From the Artemis Exploration Zone

“…In addition to standard isochron chronology, coupled 146‐147 Sm‐ 142‐143 Nd isotope systematics can be used to assess the mantle closure ages (i.e., the duration of lunar magma ocean crystallization) for the sources of lunar basalts (Boyet & Carlson, 2007; Brandon et al., 2009; McLeod et al., 2014). Finally, the nature and compositions of lunar mantle source compositions and potential mixtures can be assessed using the Sm‐Nd system (Borg et al., 2009; Srivastava et al., 2022).…”