Abstract
In order to investigate the genetic nature of the polymict breccia howardite Melrose-b, a whole-rock sample was separated into four fractions after pulverization and the rare earth element (REE) abundances were precisely determined by isotopic dilution in those fractions. Such an investigation shows that the three precipitated fine-particle fractions are depleted in Ce by the same factor (0.62 ∼ 0.64) in spite of differences in mineralogy, while the corresponding factor of Ce depletion for the suspended-matter fraction is 0.462; the smaller value indicates a greater depletion in Ce. The weight fraction values of four fractions calculated from the REE abundances are in satisfactory agreement with the actual values. The concentration ratios between plagioclase and mainly pigeonite fractions accord with those observed in similar phases of the Juvinas eucrite [1]. Moreover, the bulk pattern synthesized from the three fine-particle fractions is similar in absolute level to that for the Zmenj howardite [1]. It is concluded that the negative Ce anomaly reflects the effect predating the igneous activity in the parent planetary body.
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