¹Dian Ji, ¹Rajdeep Dasgupta, ¹Cin-Ty Lee
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.042]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, United States of America
Copyright Elsevier

The theory of the Moon’s formation via a giant impact, along with initial early sample analyses, suggested that the Moon is extremely volatile-depleted relative to the Earth. Yet, the petrologic studies of lunar melt inclusions and volcanic glasses over the last two decades suggested that water content in the lunar mantle is much higher (as high as 133 – 292 μg/g) than expected and is similar to the Earth’s shallow upper mantle. This high water concentration of the lunar mantle challenged prevailing models of the formation and early evolution history of the Moon, suggesting that not all volatiles were lost, or that impactors supplied additional volatiles. However, previous petrologic models of lunar primary melt water content reconstruction did not consider many key magma differentiation processes. Here, we model lunar magmatism taking into consideration the process of magmatic recharge and show that such a process can explain the anomalously high water abundances, along with other volatile elements such as S, F, and Cl, in Apollo sample 74220 basaltic melt inclusions, as well as the available volatile data of Apollo 79135 and 15597 basaltic to andesitic melt inclusions. Moreover, the model can also explain the MgO content and high-Ti nature of 74220 inclusions, since recharge results in ever-increasing incompatible element concentrations while buffering major element compositions. Therefore, other than deriving from a wet background mantle, we propose an alternative scenario that the water-rich lunar melts could originate from a water-poor (as low as 1–22 μg/g), primitive, magma ocean cumulate. The estimated extent of volatile depletion of the lunar interior varies with the vigor of the magmatic recharge process. Further studies are necessary to independently assess evidence of magmatic recharge, the melt replenishment frequency, and the impact of such a magma reservoir process in our understanding of lunar mantle-crust evolution.