Computer Science
Scientific paper
Oct 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996natur.383..517m&link_type=abstract
Nature, Volume 383, Issue 6600, pp. 517-520 (1996).
Computer Science
46
Scientific paper
THE elevated abundances of highly siderophile elements in the Earth's mantle, relative to what would be predicted from metal-silicate equilibrium, have often been cited as evidence for the accretion to the Earth of a 'late veneer' of chondritic material following core formation1. As rhenium and its decay-product osmium are both highly siderophile, the evolution of the Re-Os isotope system in a terrestrial reservoir provides a robust, time-averaged constraint on the siderophile abundances of the reservoir; thus, the broadly chondritic evolution of Os isotopes in the oceanic upper mantle provides strong support for the late accretion model2,3. But the Re-Os composition of the late veneer is still poorly defined, because the mantle has differentiated into 187Os-enriched and -depleted reservoirs4-7. Here we report a value for the Os isotopic composition of the modern 'primitive upper mantle' (PUM), a hypothetical undifferentiated upper-mantle reservoir. From suites of variably melt-depleted mantle xenoliths from three continents, we derive a minimum 187Os/188Os ratio for PUM of 0.1290 +/- 0.0009, by using a correlation between 187Os/188Os and geochemical indices of 'fertility' to extrapolate to the Os isotope ratio of undepleted mantle. Comparing this value to the 187Os/188Os ratios measured in different classes of chrondritic meteorite, we infer that the late veneer had siderophile element abundances similar to those of enstatite or ordinary chondrites (187Os/188Os = 0.1286 +/- 0.0010), rather than carbonaceous chondrites (0.1258 +/- 0.0005).
Meisel Th.
Morgan John W.
Walker Ray J.
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