Fusible mantle cumulates trigger young mare volcanism on the cooling Moon

Long-term reduced lunar mantle revealed by Chang'e-5 basalt

The redox state of a planetary mantle affects its thermal evolution. The redox evolution of lunar mantle, however, remains unclear due to limited oxygen fugacity (fO2) constraints from young lunar samples. Here, we report vanadium (V) oxybarometers on olivine and spinel conducted on 27 Chang'e-5 basalt fragments from 2.0 billion years ago. These fragments yield an average fO2 of ΔIW -0.84 ± 0.65 (2σ), which closely aligns with the Apollo samples from 3.6-3.0 billion years ago. This temporal uniformity indicates the lunar mantle remained reduced. This observation reveals that the processes responsible for oxidizing mantles of Earth and Mars either did not occur or had negligible oxidizing effects on the Moon. The long-term reduced mantle may lead to a distinctive volatile degassing pathway for the Moon. It could also make the lunar mantle more difficult to melt, preventing internal heat dissipation and consequently resulting in a slow cooling rate.

Melting and Rapid Solidification of Lunar Regolith Particles Returned by Chang'E-5 Mission

Melting and solidification of lunar regolith are pivotal for comprehending the evolutionary dynamics of lunar volcanism, geology, and impact history. Additionally, insights gained from these processes can contribute to the advancement of in situ resource utilization technologies, for instance additive manufacturing and resource extraction systems. Herein, we conduct the direct observation of the melting and rapid solidification of lunar particles returned by the Chang'E 5 mission. The melting temperature and melting sequence were obtained. Bubble generation, growth, and release were clearly observed, with a maximum bubble diameter of 5 µm, which is supposed to be according to the release of volatiles that embedded in the particles. During the solidification process, evident crystallization occurred with incremental crystal growth rate approximately of 27 nm/s. Scanning electron microscopy and energy-dispersive x-ray spectroscopy results verified that the Fe-rich mineral crystalizes first. These results would improve the understanding of the evolution of lunar volcanism, geology, and impact history.

Returned samples indicate volcanism on the Moon 120 million years ago

There is extensive geologic evidence of ancient volcanic activity on the Moon, but it is unclear how long that volcanism persisted. Magma fountains produce volcanic glasses, which have previously been found in samples of the Moon's surface. We investigated ~3000 glass beads in lunar soil samples collected by the Chang'e-5 mission and identified three as having a volcanic origin on the basis of their textures, chemical compositions, and sulfur isotopes. Uranium-lead dating of the three volcanic glass beads shows that they formed 123 ± 15 million years ago. We measured high abundances of rare earth elements and thorium in these volcanic glass beads, which could indicate that such recent volcanism was related to local enrichment of heat-generating elements in the mantle sources of the magma.

Low Ni and Co olivine in Chang'E-5 basalts reveals the origin of the young volcanism on the Moon

Mare basalts returned by the Chang'E-5 (CE5) mission extend the duration of lunar volcanism almost one billion years longer than previously dated. Recent studies demonstrated that the young volcanism was related neither to radiogenic heating nor to hydrous melting. These findings beg the question of how the young lunar volcanism happened. Here we perform high-precision minor element analyses of olivine in the CE5 basalts, focusing on Ni and Co. Our results reveal that the CE5 basalt olivines have overall lower Ni and Co than those in the Apollo low-Ti basalts. The distinctive olivine chemistry with recently reported bulk-rock chemistry carries evidence for more late-stage clinopyroxene-ilmenite cumulates of the lunar magma ocean (LMO) in the CE5 mantle source. The involvement of these Fe-rich cumulates could lower the mantle melting temperature and produce low MgO magma, inhibiting Ni and Co partitioning into the magma during lunar mantle melting and forming low Ni and Co olivines for the CE5 basalts. Moreover, the CE5 olivines show a continuous decrease of Ni and Co with crystallization proceeding. Fractional crystallization modeling indicates that Co decreasing with crystallization resulted from CaO and TiO2 enrichment (with MgO and SiO2 depletion) in the CE5 primary magma. This further supports the significant contribution of late-stage LMO cumulates to the CE5 volcanic formation. We suggest that adding easily melted LMO components resulting in mantle melting point depression is a key pathway for driving prolonged lunar volcanism. This study highlights the usefulness of olivine for investigating magmatic processes on the Moon.

Surges in volcanic activity on the Moon about two billion years ago

The history of mare volcanism critically informs the thermal evolution of the Moon. However, young volcanic eruptions are poorly constrained by remote observations and limited samples, hindering an understanding of mare eruption flux over time. The Chang'e-5 mission returned the youngest lunar basalts thus far, offering a window into the Moon's late-stage evolution. Here, we investigate the mineralogy and geochemistry of 42 olivine and pyroxene crystals from the Chang'e-5 basalts. We find that almost all of them are normally zoned, suggesting limited magma recharge or shallow-level assimilation. Most olivine grains record a short timescale of cooling. Thermal modeling used to estimate the thickness and volume of the volcanism sampled by Chang'e-5 reveals enhanced magmatic flux ~2 billion years ago, suggesting that while overall lunar volcanic activity may decrease over time, episodic eruptions at the final stage could exhibit above average eruptive fluxes, thus revising models of lunar thermal evolution.