KREEP-rich breccia in Chang'E-5 regolith and its implications

Lunar breccias provide crucial insights into the lithological diversity,shock processing and evolution of the lunar crust.Here,we report a unique regolith breccia(CE5C0000YJYX070GP,hereafter CE5C)returned from the Chang'E-5(CE-5)mission.CE5C is one of the largest CE-5 breccias with a wide variety of lithologies,dominated by basaltic and mineral fragments as well as impact-melted clasts(including mid-Ti glasses,high-Al glasses,and crystal-bearing impact melt clasts).A comprehensive study of petrology and mineralogy on several representative clasts was conducted by integrating Scanning Electron Microscopy(SEM),Tescan Integrated Mineral Analysis(TIMA),Electron Probe Microanalysis(EPMA)and Laser Ablation Inductively Coupled Plasma Mass Spectrometry(LA-ICP-MS)techniques.Evidence is sufficient that CE5C is a mixed mare-highland regolith breccia,with a high percentage of KREEPy material(>20 vol.%),which has not been previously reported in other CE-5 samples.The mid-Ti impact glasses are characterized by high FeO(24.0 wt.%)and intermediate TiO_(2)(5.5 wt.%)contents,while the high-Al impact glasses have a chemical composition compatible with KREEP.Integrated with the regional geological context of the CE-5 landing site,we propose that CE5C is likely derived from a mixed region between the P58/Em4 mare unit and its contiguous eastern highlands.Despite the difficulty in assessing the representativeness of CE5C,the substantial presence of KREEPy material may provide valuable clues to the provenance of exotic ejecta,including the identification of unrecognized source craters situated in the eastern periphery of the sampling unit.

Mineral chemistry and 3D tomography of a Chang’E 5 high-Ti basalt:implication for the lunar thermal evolution history

In December 2020, Chang’E-5(CE-5), China’s first lunar sample return mission, successfully collected samples totaling 1731 g from the northern Oceanus Procellarum. The landing site was located in a young mare plain, a great distance from those of Apollo and Luna missions. These young mare basalts bear critical scientific significance as they could shed light on the nature of the lunar interior(composition and structure) as well as the recent volcanism on the Moon. In this article, we investigated a CE-5 basalt sample(CE5 C0000 YJYX065) using a combination of state-of-art techniques, including high resolution X-ray tomographic microscopy(HR-XTM), energy dispersive X-ray spectroscopy(EDS)-based scanning electron microscope(SEM), and electron probe microanalysis(EPMA) to reveal its 3 D petrology and minerology.Our results show that this sample has a fine-to medium-grained subophitic texture, with sparse olivine phenocrysts setting in the groundmass of pyroxene, plagioclase, ilmenite and trace amounts of other phases. It has an extremely high ilmenite modal abundance(17.8 vol%) and contains a significant amount(0.5 vol%) of Ca-phosphate grains. The mineral chemistry is in excellent agreement with that of Apollo and Luna high-Ti basalts. The major phase pyroxenes also display strong chemical zoning with compositions following the trends observed in Apollo high-Ti basalts. Based on current data, we came to the conclusion that CE5 C0000 YJYX065 is a high-Ti mare basalt with a rare earth element(REE) enriched signature. This provides a rigid ground-truth for the geological context at the CE-5 landing site and clarifies the ambiguity inferred from remote sensing surveys.