Remote sensing observations have shown that the far side of the Moon (lunar farside) has different geology and rock composition to those of the nearside, including the abundances of potassium, rare earth elements, and phosphorus (collectively known as KREEP). The Chang’e-6 (CE-6) spacecraft collected samples from the South Pole–Aitken (SPA) basin on the farside and brought them to Earth. We used lead-lead and rubidium-strontium isotope systems to date low-titanium basalt in a CE-6 sample, finding a consistent age of 2830 (±5) million years. We interpret this as the date of volcanism in SPA and incorporate it into lunar crater chronology. Strontium, neodymium, and lead isotopes indicate that the volcanic magma was from a lunar mantle source depleted in incompatible elements and containing almost no KREEP component.

Whether arc mantle is more oxidized than oceanic mantle is persistently debated. The behavior of multivalent vanadium (V) is oxygen fugacity (fO₂) sensitive, and the ratios of V to a homovalent element (e.g., Sc, Ti, or Yb) in basalts were commonly used as fO₂ proxies. Similar ratios, such as V/Sc, between arc basalts and mid‐ocean ridge basalts were previously taken as evidence for similar fO₂s in their mantle sources. However, this claim may be problematic because elemental ratios are primarily controlled by partition coefficients (D values), which are further affected by various factors. Here we determined D values of V and other transition elements between mantle minerals and basaltic melts at typical arc T–P‐H₂O conditions and variable fO₂s. Combining experimental results with published data, the effects of fO₂, T, P, and phase compositions on D_V, D_Sc, and D_Ti for olivine, orthopyroxene (opx), clinopyroxene (cpx), and spinel were evaluated using multiple linear regressions. The results show that D_V values for these four minerals all increase with decreasing fO₂ and temperature, leading to higher D_V/D_Sc and D_V/D_Ti ratios at low temperatures than those at high temperatures given a certain fO₂. Thus, similar V/Sc and V/Ti ratios between arc basalts and mid‐ocean ridge basalts reflect a relatively oxidized arc mantle due to its lower melting temperatures. In light of the highly incompatible behavior of Ti during mantle melting, V‐Ti systematics are regarded to be more superior than V‐Sc systematics in the fO₂ estimation. Partial melting modelling results using V‐Ti systematics reveal that arc mantle is, on average, ~0.9 log units higher in fO₂ than oceanic mantle.

The combined study of Ce and Nd stable isotopes is promising because Ce and Nd behave similarly in geological processes and distinctively in redox reactions. However, the sequential purification of Ce and Nd from other REEs is particularly challenging because of their similar physicochemical properties. In this contribution, we present a novel two-stage ion-exchange chromatography method to purify Ce and then Nd using Bio-Rad AG50W-X12 (200–400 mesh) and Eichrom TODGA resin (50–100 μm). The yields of Ce and Nd are both typically more than 99.3% after measurements of natural materials. The potential influence of the HCl content and rock type were thoroughly evaluated. Stable Ce and Nd isotopic ratios were measured by MC-ICPMS and calibrated with Sm and Eu internal standards, respectively. The long-term external reproducibility was better than ±0.04‰ (2SD) for δ^142/140Ce and ±0.03‰ (2SD) for δ^146/144Nd. The stable Ce and Nd isotopic ratios of ten commercially accessible geological rocks were measured here. The δ^142/140Ce values of four geological rocks were presented for the first time. Other results are in good accordance with reported values within analytical uncertainties. The similarity in the degree of Ce and Nd isotopic fractionation may be induced by diagenetic processes, whereas the difference may be accused by redox reactions. In addition, our method using a single sample aliquot can help to minimize the consumptions and heterogeneities of the samples. This procedure for a two-stage isolation of Ce and Nd and high-precision analysis of their isotopic ratios has important advantages in the study of Ce and Nd isotope geochemistry.