HR: 0800h
AN: U21B-0403    [Abstracts]
TI: The role of sulfur in the Earth's formation
AU: * javoy, m
EM: marc.javoy@wanadoo.fr
AF: Université Denis Diderot, 2 place jussieu, Paris Cedex 05, 75251, France, Metropolitan
AU: * javoy, m
EM: marc.javoy@wanadoo.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris Cedex 05, 75251, France, Metropolitan
AB: When sulfur is considered in the Earth's formation it is mostly because of its possible role in lowering the density of the Core. This, however, looks less and less likely as experimental studies of its effects on other physical properties of the Core progress. On the contrary it could have important effects on the relative concentrations of other elements, like the refractory lithophile elements (RLE). « Reference » Earth models have not basically changed for the last thirty years and they more or less rely on two basic assumptions : 1- One can, by a way or another, retrieve a « primitive » mantle composition from the composition of accessible peridotite samples. 2- In that primitive composition the ratios of RLE concentrations are equal to those in the CI chondrites (that is essentially one chondrite, Orgueil). These two hypotheses, when looking carefully at the sets of data from which they derive are somewhat conjectural and the best balanced discussion of their possible use still remains that of Hart and Zindler (1), more than 20 years ago. It appears more and more that the reducing phase through which the Earth-forming materials had to go to render possible the formation of the Core was characterized, among other things, by high sulfur fugacities. This does not mean necessarily that the final sulfur concentration of the Earth is high, because these high sulfur fugacities were probably labile at the million years' scale. But these sulfur fugacities induced a partitioning of elements between the sulfide phases, the metal and the silicates. Since the accretion of the Earth involved a somewhat random mixing of these three phases' categories, the partitioning of elements, and, for example the so called Refractory Lithophile Elements (RLE), depended largely on the relative stability of their sulfides. This is true for example of the Ca/Al ratio. Ca is very concentrated in the sulfides, whereas Al resides mainly in the silicates. Other elements will be similarly fractionated, wether they are refractory (eg U, some REE) or volatile (K vs Na) Hence, if part of the very limited and very biased sampling of the Earth's Mantle can somehow retrieve some of the chondritic RLE ratios, this is probably much more because of correcting effects of silicate partial melting during accretion, than by a magic stability of these ratios. (1) Hart S.R. & Zindler Chem. Geol. 57 247-267 1986
DE: 1000 GEOCHEMISTRY
SC: Union [U]
MN: 2007 Fall Meeting