Mathematics – Logic
Scientific paper
Oct 1968
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1968gecoa..32.1087t&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 32, Issue 10, pp.1087-1109
Mathematics
Logic
14
Scientific paper
Replicate neutron-activation determinations of Ga, Ge, In and Ir have been carried out in 26 members of the L-group chondrites, including at least 6 members of each of the known petrologic types. Indium varies by a factor of 1000 within the suite, from a high of 55 ppb in Hallingeberg to a low of 0·048 ppb in Peace River. The indium concentrations are strongly correlated with those of primordial Ar 36 and Xe 132 , total C, and with the degree of inhomogeneity of the ferromagnesium silicates. These data cannot be explained by any of the current theories for the fractionation of volatile elements, though the addition of a third component to the Anders two-component model seems to provide a means for explaining the variations. Even so, the remarkable anti-correlation of In and the rare gases with evidence of metamorphism remains enigmatic. Concentrations of the siderophilic elements, Ga, Ge and Ir, are not correlated with petrologic type, nor with In or rare gas concentration. These elements are positively correlated with the Ni and metallic Fe contents of the meteorites, and negative correlations are found between the concentrations of Ga, Ir, Ni, and metallic Fe and the Fe/Fe + Mg ratios of the olivine. If data from 6 chondrites which may be members of the LL group are discarded, the strength of the correlations is greatly reduced, but the true situation is believed to be closer to that represented by the data as a whole. A model is proposed which accounts for the observations; according to this model a metal-silicate fractionation occurred in such a way that the final oxidation state of the silicate inversely correlated with the metal-silicate ratio, but Prior's rules do not hold in the quantitative sense. The metal-silicate fractionation is thought to have occurred during the accretion of the parent body, in which case a portion of the metal along with some reducing material may have represented an additional component of the primative solar nebula.
Tandon Shyam N.
Wasson John T.
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