Young volcanic flow deposits on the Moon are associated with a region enriched in potassium, rare earth elements, and phosphorous (KREEP) known as the Procellarum-KREEP-Terrane, a region known to have elevated temperatures due to the concentration of radioactive heat-producing elements such as uranium, thorium, and potassium. Ultraviolet and visible light spectra collected during the Clementine mission suggest that stratigraphically younger lava flows have lower olivine abundances than older flows. The Chang’e-5 mission recently returned samples of these younger lava flows, allowing for a more comprehensive analysis of their composition.
A team led by Yuqi Qian from the China University of Geosciences analyzed the chemical composition of young volcanic flows in the Procellarum-KREEP-Terrane and determined that they are compositionally distinct from older deposits in surrounding lunar nearside basins. After comparing remote sensing data, analysis done on the Moon by the Chang’e-3 rover, and samples returned from Chang’e-5, the team found that the younger lava flows only have 8.5±2.6% olivine, much less than the estimation of 50±10% from Clementine. Measurements of basalts taken by the Chang’e-3 spectrometer show significantly higher olivine abundances, although these are also lower than those reported through pure remote sensing studies. Combining data from Chang’e-3, Chang’e-5, and crater counting statistics, the team further determined the relative ages of several flow units: lava flows near Chang’e-3 have ages of approximately 1.4 billion years (Ga), whereas flows where the Chang’e-5 samples have older ages of 2 Ga.
The multifaceted approach of this study highlights the need for sample return missions to the Moon to facilitate more detailed compositional analysis than can be accomplished remotely.
Compositional differences between individual lava flows are too small-scale to be captured by orbital measurements but provide key information to further understand the history of lunar volcanism. READ MORE