Compositional dispersions in lunar and terrestrial basalts

Abstract

The dispersions in composition observed among samples of terrestrial basalts with known field relationships are compared with those of various subgroups of lunar mare basalts. The comparison indicates that there are no substantial reasons based on trace-element data to require that large numbers of different basalts were sampled at each Apollo site. The Apollo 15 olivine and quartz normative basalts and the Apollo 12 ilmenite and olivine basalts show compositional variations which are no more pronounced than those found within single terrestrial flows, whose inhomogeneity in horizontal section has been demonstrated. The inhomogeneities of the parent rocks in the case of the Apollo 12 and 15 basalts on a scale of centimeters overshadow any differences which might exist among different general regions of the lava flows from which these samples might have derived.