Element correlations and the bulk composition of the Moon

Abstract

A great number of element correlations have been observed in lunar samples. It is known from theoretical and experimental studies that in the solar nebula the elements condensed in groups according to their condensation temperatures and chemical affinities. One of these groups - the refractory elements - is represented by the early condensates or high temperature condensates (h.t.c.). From element correlations and group relations we estimate the bulk Moon to contain about 50 % of h.t.c.; the other 50%, the non-refractory portion, consists mainly of (Mg, Fe)-silicates and minor phases of about chondritic composition. Recently we have found strong evidence that most of the lunar highland samples represent mechanical mixtures of a differentiated (feldspathic) lunar component and a primary component from the last accretion stage of the Moon. The contribution of the h.t.c. in this primary material is estimated to 21 %. Hence, an inhomogeneous accretion of the Moon is indicated. After the formation of a highly refractory core relatively more and more non-refractory material was added until the Moon reached its final mass. The composition of the primary matter observed in the lunar highlands gives us an important clue to the composition of the non-refractory portion of the Moon and thus leads to a more reliable estimation of the lunar bulk composition.