Lunar Solid-type and Liquid-type Materials and Rare-earth Abundances

Abstract

CHEMICAL analyses of lunar samples have revealed that the chondrite-normalized rare-earth patterns are quite different in materials from Mare Tranquillitatis and Oceanus Procellarum (and the Fra Mauro region). The purpose of this communication is to point out that such a difference in the rare-earth (RE) pattern is closely associated with the overall evolution of lunar material and provides a clue to the genetic relationship or nature of the samples returned from the areas mentioned. Such an apparent difference in RE pattern does not represent the mutually unrelated aspects, but represents, so to speak, both sides of the same coin. (It is quite difficult to obtain such a clue from trace elements other than the RE elements.) One important aspect of RE geochemistry is that it allows a discussion of the relationship of co-existing liquid and solid by a mathematically strict but simple treatment, namely division by certain defined coefficients. The situation is, however, sometimes complicated a little by a uniform enrichment effect that applies to all RE.