Siderophile elements partitioning

Chondrite-normalized abundances of siderophile elements in the Earth s mantle. The measured concentrations do not match those expected from low-pressure metal-silicate partition coefficients determined by experiments. Modified from Tolstikhin and Kramers (2008). 

Nevertheless, we can make some general statements about the geochemistry of differentiated planets. The planetesimals from which they accreted had compositions determined largely by element volatility. Once assembled into a planet and heated, the partitioning of elements into cores and mantles was governed by their siderophile or lithophile affinities. Further differentiation of mantles to form crusts was controlled by the compatible or incompatible behavior of elements. 

Righter, K., Drake, M. J. and Yaxley, G. (1999) Prediction of siderophile element metal-silicate partition coefficients to 20 GPa and 2800 °C the effects of pressure, temperature, oxygen fugacity, and silicate and metallic melt compositions. Physics of the Earth and Planetary Interiors, 100, 115—134. 

Chabot N. L. and Jones J. H. (2003) The parameterization of solid metal-liquid metal partitioning of siderophile elements. Lunar Planet. Sci. XXXIV, 1004. The Lunar and Planetary Institute, Houston (CD-ROM). 

Righter K. and Drake M. J. (1999) Effect of water on metal-silicate partitioning of siderophile elements a higji pressure and temperature magma ocean and core formation. Earth Planet Sci. Lett. 171, 383—399. 

Although the abundances and partition coefficients of some of the elements used to test these models are not well established, sufficient knowledge exists to render all of them problematic. Model (vii) appears to work well for some moderately siderophile elements. Righter and Drake (1999) make the case that the fit of the... 

Walter M. J., Newsom H. E., Ertel W., and Holzheid A. (2000) Siderophile elements in the Earth and Moon Metal/silicate partitioning and implications for core formation. In Origin of the Earth and Moon (eds. R. M. Canup and K. Righter). University of Arizona Press, Tucson, pp. 265-289. 

RSEs comprise two groups of metals the HSEs—osmium, rhenium, ruthenium, iridium, platinum, and rhodium with metal/silicate partition coefficients >10" —and the two moderately siderophile elements—molybdenum and tungsten (Table 2). As the major fractions of these elements are in the core of the Earth, it is not possible to establish independently whether the iDulk Earth has chondritic ratios of RLE to RSE, i.e., whether ratios such as Ir/Sc or W/Hf are chondritic in the bulk Earth. Support for the similar behavior of RLE and RSE in chondritic meteorites is provided by Figure 9. The ratio of the RSE, Ir, to the nonrefractory siderophile element, Au, is plotted against the ratio of the RLE, Al, to the nonrefractory lithophile element, Si. Figure 9 demonstrates that RLEs and RSEs are correlated... 

Holzheid A., Sylvester P., O Neill H., St C., Ruble D. C., and Palme H. (1998) Late chondritic veneer as source of the highly siderophile elements in the Earth s mantle insights from high pressure-high temperature metal-silicate partition behavior of Pd. Nature 406, 396-399. 

Partitioning Behavior of Siderophile Elements Effects of P, T.fo, and Composition... 

Differentiation of terrestrial planets includes separation of a metallic core and possible later fractionation of mineral phases within either a solid or molten mantle (Figure 1). Lithophile and siderophile elements can be used to understand these two different physical processes, and ascertain whether they operated in the early Earth. The distribution of elements in planets can be understood by measuring the partition coefficient, D (ratio of concentrations of an element in different phases (minerals, metals, or melts)). 

Partitioning of siderophile elements between metal and silicate liquid can be understood in terms of simple equilibria such as... 

The behavior of some siderophile elements is controlled by the composition of the metal, and, in particular, the Fe/Ni ratio. Because the activity coefficient of a siderophile element, M, may be different in a nickel-rich metal than an iron-rich metal, an understanding of this effect is necessary before partition coefficients can be successfully applied to a natural system. A good example is tin, which has a low activity coefficient in iron-rich metal, and a high activity coefficient in nickel-rich metal (Figure 8 Capobianco et al., 1999). Metal composition can change as a function of/o, and this can then change the solubility in the silicate melt. In addition, the Fe/Ni ratio in metal is sometimes used to impose a specific/o on a system. These effects are linked and must be unraveled first in order to understand tin in planetary mantles (Righter and Drake, 2000). 

Fleet M. E., Liu M., and Crocket J. H. (1999) Partitioning of trace amounts of higjily siderophile elements in the Fe—Ni— S system and their fractionation in nature. Geochim. Cosmochim. Acta 63, 2611—2622. 

Hillgren V. J. (1993) Partitioning behavior of moderately siderophile elements in Ni-rich systems implications for the Earth and Moon. PhD Thesis, University of Arizona, 119p. 

Hillgren V. J., Drake M. J., and Rubie D. C. (1996) High pressure and higji temperature metal/siUcate partitioning of siderophile elements the importance of silicate liquid composition. Geochim. Cosmochim. Acta 60, 2257-2263. 

Jana D. and Walker D. (1997b) The influence of sulfur on partitioning of siderophile elements. Geochim. Cosmochim. Acta 61, 5255-5277. 

Righter K. (2003) Metal/silicate partitioning of siderophile elements and core formation in the early Earth. Ann. Rev. Earth Planet. Sci. 31, 135—174. 

Righter K., Drake M. J., and Yaxley G. (1997) Prediction of siderophile element metal—silicate partition coefficients to 20 GPa and 2,800 °C the effect of pressure, temperature,/o and silicate and metalhc melt composition. Phys. Earth... 

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