ELEMENTAL ABUNDANCES IN STONE METEORITES

Abundances of Na, Al, Sc, Cr, Mn, Fe, Co and Cu have been measured by instrumental neutron activation analyses of 103 chondrites and 17 achondrites. In many cases, analyses were made of replicate samples from the same meteorite. Various sources of error in the method, including sampling errors, are discussed in detail. Examination of the patterns of coherence of the elements we have determined suggests that we can perceive effects of fractionation during condensation from the solar nebula of matter parental to chondrites. Such effects seem to be exhibited both in the abundances of lithophilic elements, perhaps being related to varied temperatures of accretion and in the abundances of those elements which would be affected by metal-silicate fractionation in the solar nebula. Atomic abundances relative to Si vary little in carbonaceous chondrites, suggesting that efficient mixing processes operated on these meteorites prior to or during their formation. We suggest that at present, no single class of carbonaceous chondrites is clearly more primitive than another. Carbonaceous and unequilibrated ordinary chondrites may represent aggregates of material accreted from the solar nebula at relatively low temperatures, as many recent discussions of these meteorites would suggest. Our data support a model of equilibration and minor mobilization of non-volatile elements within small domains of chondrites after accretion. Such a model would be consistent with the petrologic types of Van Schmus and Wood (1967). Achondrites do not exhibit simple regularities in lithophilic elemental abundances as do chondrites. Models for the origins of achondrites surely must include effects of magmatic fractionation, but we do not at present have enough information to assess the plausibility of such models.