Constraints on the Geochemical Variations and Evolution of the Lunar Crust and Mantle as Revealed

Introduction: Basaltic volcanism is a fundamental process that has occurred on most terrestrial planets like Earth, Moon, and Mars. As partial melts of planetary interiors, basalts have compositions that reflect the planet’s bulk composition, its oxidation state, and the size and composition of its core. Several previous studies have compared bulk-rock major-, minor-, and traceelement compositions of basalts to understand differences among the terrestrial planets [1,2]. Other studies have recognized that minor and major element compositions of silicate phases in basalts reflects the chemical and physical conditions of the melt from which they crystallized, and can be used to differentiate distinct origin and settings [e.g., 3-5]. In particular the Fe/Mn ratios of basalts and their minerals do not change much during basalt genesis and fractionation. Therefore, it is not surprising that this ratio is used to categorize the basaltic source compositions (i.e. mantles) and is used as a discriminant among particular planetary bodies, e.g. Moon vs. Earth vs. Mars [5-7].