Abstract: Initally, the elevated delta-37 Cl values of lunar materials were attributed to volcanic degassing[1]. However, chlorine isotope ratios of apatite in lunarmare basalts appear to reflect mixing between two reservoirs.One component, with elevated delta-37 Cl is greater than or equal to + (25%) ([2] may represent the urKREEP–the final product of the crystallization of the lunar magma ocean. The second component, with delta-37 Cl is approximately (0%), is inferred to represent either a mare bas…