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.

Stepped-up development of accelerator mass spectrometry method for the detection of ^(60)Fe with the HI-13 tandem accelerator

The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae.Lunar samples retain valuable information from these events,via detectable long-lived“fingerprint”radionuclides such as^(60)Fe.In this work,we stepped up the development of an accelerator mass spectrometry(AMS)method for detecting^(60)Fe using the HI-13tandem accelerator at the China Institute of Atomic Energy(CIAE).Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph,a Wien filter with a maximum voltage of±60 kV and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide^(60)Fe.A 1μm thick Si_(3)N_(4) foil was installed in front of the Q3D as an energy degrader.For particle detection,a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph.Finally,an^(60)Fe sample with an abundance of 1.125×10^(-10)was used to test the new AMS system.These results indicate that^(60)Fe can be clearly distinguished from the isobar^(60)Ni.The sensitivity was assessed to be better than 4.3×10^(-14)based on blank sample measurements lasting 5.8 h,and the sensitivity could,in principle,be expected to be approximately 2.5×10^(-15)when the data were accumulated for 100 h,which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.

Chang’e-5 samples reveal two-billion-year-old volcanic activity on the Moon and its source characteristics

The Chang’e-5 mission returned new lunar samples after the last sample mission of the Moon 44 years ago,and is also the first mission that China has completed the sampling of extraterrestrial bodies.Recently,independent teams from the Institute of Geology,Chinese Academy of Geological Sciences,and the National Astronomical Observatories and the Institute of Geology and Geophysics,Chinese Academy of Sciences reported the first batch of results of Chang’e-5 lunar samples.The basic physical properties of the Chang’e-5 soil are within the range of the Apollo and Luna samples though the Chang’e-5 soil is finer-grained,better sorted,and has a slightly lower true density than the mare basalt previosuly reported.The Pb-Pb dating of U-rich minerals in the Chang’e-5 basalt clasts indicated that they formed at about 2.0 Ga,800 million years younger than the youngest lunar sample recovered previously(2.8 Ga),confirming that lunar volcanic activity can last at least until 2 Ga.In-situ Sr-Nd isotope analyses suggested that the Chang’e-5 basalt originated from a depleted mantle source.The contribution of the KREEP component is less than 5%,which excluded the hypothesis that KREEP-rich sources provide an additional heat source for mantle melting.In addition,water contents and H isotopes of apatite and melt inclusions of the Chang’e-5 basalt suggested that the source region is not rich in water which can lower the melting point.Therefore,the reason why lunar volcanic activity can last so long is still unclear,which is a new direction for future lunar exploration and research.