Evidence for a late chondritic veneer in the Earths mantle from high-pressure partitioning of palladium and platinum
Date
2000
Authors
Holzheid, A
Sylvester, Paul
O'Neill, Hugh
Rubie, David
Palme, Herbert
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Macmillan Publishers Ltd
Abstract
The high-pressure solubility in silicate liquids of moderately siderophile 'iron-loving' elements (such as nickel and cobalt) has been used to suggest that, in the early Earth, an equilibrium between core-forming metals and the silicate mantle was established at the bottom of a magma ocean. But observed concentrations of the highly siderophile elements - such as the platinum-group elements platinum, palladium, rhenium, iridium, ruthenium and osmium - in the Earth's upper mantle can be explained by such a model only if their metal-silicate partition coefficients at high pressure are orders of magnitude lower than those determined experimentally at one atmosphere (refs 3-8). Here we present an experimental determination of the solubility of palladium and platinum in silicate melts as a function of pressure to 16 GPa (corresponding to about 500 km depth in the Earth). We find that both the palladium and platinum metal-silicate partition coefficients, derived from solubility, do not decrease with pressure - that is, palladium and platinum retain a strong preference for the metal phase even at high pressures. Consequently the observed abundances of palladium and platinum in the upper mantle seem to be best explained by a 'late veneer' addition of chondritic material to the upper mantle following the cessation of core formation.
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Keywords: cobalt; iridium; nickel; osmium; palladium; platinum; rhenium; ruthenium; chondrite; high pressure; mantle chemistry; palladium; partitioning; platinum; article; partition coefficient; physical chemistry; priority journal; solubility; temperature
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Nature
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Journal article
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2037-12-31