From Magma-Ocean Cumulates to Melt Inclusions: Constraints on Lunar Mantle Water

Kurzfassung

Water in the Moon’s interior exerts a primary control on the generation of mare basalts and pyroclastic deposits by lowering the mantle solidus and enhancing melt productivity. These volcanic products represent localized melting of the lunar mantle, and their occurrence depends on the distribution of water in the mantle. However, estimates of lunar mantle water contents span multiple orders of magnitude, from as little as ~64 ppb [1] to as much as ~260 ppm H2O [2]. Such a wide range implies markedly different magmatic evolutions for the Moon, from limited, episodic volcanism to fluxes nearing those of terrestrial upper mantle contains ~50–200 ppm H2O [3].

The wide range of inferred lunar mantle water contents reflects uncertainties in the initial water budget of the lunar magma ocean (MO) and its crystallization history. Additional controls include redox conditions, volatile loss during MO degassing, and the partitioning of water into nominally anhydrous minerals (NAMs) that constitute the mantle cumulates. Among these factors, the mineral–melt partition coefficients (or D) for H2O in orthopyroxene and clinopyroxene are particularly important, as these phases dominate much of the lunar upper mantle [4]. Yet, existing constraints on D for NAMs are sparse for Fe-rich compositions and reducing conditions relevant to lunar MO crystallization. This study aims to experimentally constrain pyroxene D values for lunar MO conditions and link mantle cumulate H2O contents to source regions of basalts via batch melting.