Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmmr43b1878c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #MR43B-1878
Mathematics
Logic
[1015] Geochemistry / Composition Of The Core
Scientific paper
Sulfur is an important component of protoplanetary cores, as indicated by the presence of sulfides in iron meteorites, as well as the trace element distributions within iron groups that indicate a fractional crystallization process between metal and coexisting sulfide melt. However, sulfur in the Earth’s core is expected to be limited to 2 percent or lower, as indicated by the volatility trend of elements in the bulk Earth (Dreibus and Palme, 1996; McDonough, 2003). This follows an assumption that the order of element volatilities determined in condensation calculations for the solar nebula is also appropriate to the devolatilization of planetary bodies such as the Earth, although planets may have devolatilized by non-nebular processes. The assumption can be evaluated by applying the same logic to the iron meteorites as has been applied to the Earth; the irons exhibit volatility depletions among trace siderophile elements that are similar or greater than the volatile depletions in Earth. Estimates of S content in parent metallic melts have been reported for the IIAB, IID, IIIAB, IVA, and IVB iron meteorite groups (e.g., Chabot, 2004; Wasson and Huber, 2006). Although there are discrepancies between some models, in most cases one finds that the cosmochemical estimates of S abundance in these protoplanetary cores are significantly higher than would be expected on the basis of their volatility trends. For example, CI-normalized S/Ge ratios exceed 100 in some cases. Unless the crystallization models applied to the iron meteorite groups are inaccurate, the assumptions behind the construction of the volatility trends appear to be violated for S in protoplanets (and by extension larger planets, including Earth). Hence, it remains plausible on cosmochemical grounds that Earth’s core is S-rich. Gas speciation and partial pressures in the impact plumes produced during planet formation are very different than those in the low-density, hydrogen-rich solar nebula, and should generate a different volatilization-condensation sequence.
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