A clue to the genesis of lunar anorthositic rocks: “Non-anorthitic” silica as a geochemical indicator

Abstract

A new quantity, non-anorthitic silica (nasa), is defined in this paper. Empirically, there is a logarithmically linear relationship between RE and nasa for Apollo 16 samples including typical anorthosites. Extension of this line appears to pass through KREEP. Mare basalts form a different series in this diagram. Based on RE patterns, in particular, Ce anomaly and on the oldest age of Apollo 16 anorthositic complexes, it is suggested that we had better reserve the speculation that anorthosites originated mostly from the anorthositic planetesimals which formed from the gases derived from the earth's silicate surface. Furthermore, it might be imagined that the earth's surface material had been more or less fractionated at the time of evaporation. The RE data on 60015 and 15016 are presented. For 60015, both main inner part (anorthosite) and dark coating were investigated.