A Raman Spectroscopic and Microimage Analysis Perspective of the Chang'e-5 Lunar Samples

The Chang'e-5 (CE-5) materials represent the youngest returned lunar samples. We performed a detailed Raman spectroscopic survey (1259-point Raman modal analysis) to evaluate the mineralogical characteristics of CE-5 soils, constraining the source materials and shock effects of these unique samples. The mineral chemistry (e.g., Mg#(3-)(60) for mafic minerals) and modal abundance (first distinguishing basaltic and feldspathic glasses) of CE-5 mare soils are different from those of Apollo high- and low-Ti basalts, possibly representing an intermediate-Ti mare basalt. The occurrence of minor Mg-rich materials (Mg# > 70) provides evidence of contamination from similar to 5% to 7% exogenous materials, possibly related to Mg-suite rocks. The microimage analyses suggest that the CE-5 soils are fine-grained, mature, and unimodal particle-size distribution, highlighting that micrometeorite reworking dominates the CE-5 regolith evolution with minor mixing from nonmare materials. The pressure-sensitive minerals (quartz and maskelynite) indicate that 17-25.8 GPa shock pressures might be the higher limit in a relatively young lunar terrain. Plain Language Summary The returned Chang'e-5 (CE-5) samples from one of the youngest mare units in northern Oceanus Procellarum on the Moon provide vital clues about late lunar thermal evolution and post deposition processes (e.g., space weathering and mixing effects) on the lunar surface, presenting quite different chemistry from typical Apollo soils. The mineralogy, geochemistry, and chorology of CE-5 samples have been done, while new knowledge on the noncrystalline and pressure-sensitive phases, as well as nonmare materials in the soils, is still insufficient. Here, we report the mineralogic characteristics of CE-5 soils using Raman spectroscopy. Our results suggest the closest affinities in composition and modal mineralogy among the CE-5 materials but distinct from Apollo mare soils, possibly representing a new type of mare basalt (intermediate-Ti) with a minor amount (similar to 5%-7%) of exogenous contribution. The intermediate-Ti CE-5 samples have similar mineralogy and composition to the Chang'e-3 basalts, erupting in the same volcanic episode and representing the latest lunar magmatism near 2.0 Ga in the Procellarum KREEP Terrane. We constrained relatively weaker shock pressures of the CE-5 samples than Apollo highland materials. The CE-5 soils can help establish a new "ground truth" for mineralogical and compositional investigations of the lunar global surface.