Compositional Trends among Iid Rons; Their Possible Formation from the P- Rich Lower Magma in a Two-layer Core

Introduction. It was previously known that S contents were low in the two volatile depleted magmatic iron-meteorite groups IVA and IVB. Group IID, with 21 members, the fourth largest magmatic group, also has a low S content but has high contents of other volatiles. We suggest that this surprising juxtaposition is best understood by two episodes of core formation, with the IID irons forming from the high-temperature, high-P inner magma. We gathered INAA data for 19 IID irons, 18 of which were not previously studied by this technique. The data confirm previous studies showing that the IID irons formed by fractional crystallization. Evidence of a low S content in group IID. Two kinds of evidence indicate low S in the initial IID magma. 1) Buchwald [1] called attention to the low S contents observed in sections of IID irons. The observed amount of FeS in irons reflects a combination of the degree of melt trapping and the S content of the melt. If we assume that, on average, the degree of melt trapping is similar in the magmatic groups, then one can conclude that a group that has uniformly low modal FeS contents had a low S in the parental magma.