Condensation and the composition of iron meteorites |
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| Authors: | DW Sears |
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| Institution: | Department of Metallurgy, The University of Manchester, Manchester U.K. |
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| Abstract: | The pressure-temperature conditions in the primordial nebula which could produce the observed Ni, Ga and Ge abundances in the major iron meteorite groups have been calculated assuming equilibrium condensation. Included in these calculations are the effect on the metal composition of Fe oxidation and sulphide formation during accretion, GeS and GaCl in the nebula gases and pressure variations in the nebula. It was found that the IIAB irons had their abundances of these elements fixed at the low-pressure extreme of the range which gives the IAB irons, but at 50 ± 10K higher temperatures. IIIAB and IVA formed over the same temperature range as IAB (600–670?40+60 K) in regions where the pressure was lower by a factor of 20 and 104 respectively. Group IVB accreted soon after condensation of the metal and at pressures of less than 10?3 atmosphere. The distribution of sulphur and carbon are consistent with this. The abundance of carbon in group IAB suggests that this and group IIAB accreted at about 10?4 atmosphere, so that IIIAB and IVA accreted where the pressure was 5 × 10?6 and 10?8 atmosphere, respectively. |
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