Siderophile elements pressure

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). 

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. 

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. 

The major problem presented by the Earth s chemical composition and core formation models is providing mechanisms that predict correctly the siderophile element abundances in the Earth s upper mantle. It long has been recognized that siderophile elements are more abundant in the mantle than expected if the sihcate Earth and the core were segregated under low-pressure and moderate-temperature equilibrium conditions (Chou, 1978 Jagoutz et al, 1979). Several explanations for this siderophile excess have been proposed, including ... 

The geochemical models of Wanke and Dreibus (1988), Lodders and Fegley (1997), and Sanloup et al. (1999) suggest that the core comprises 20.6-23.0% of the mass of Mars. All these model cores are sulfur rich, but differ significantly in core mass and sulfur abundance (Table 5). Measured siderophile element abundances in martian meteorites are consistent with equilibrium between sulfur-bearing metal and silicate at high temperature and pressure (Righter and Drake, 1996). 

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. 

The effect of oxygen pressure on the solubihties of siderophile elements in silicate melt has been understood for many years due to metallurgical interest, and has been known to the geological community since early work of Newsom and Drake (1982, 1983) on tungsten and phosphorus. Although there was a brief exploration of the possibility of zero valence dissolution of nickel and possibly cobalt at low /o (Colson, 1992 ... 

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. 

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... 

However, when calculations are made to compare the measured siderophile element depletion in the mantle with the expected values, there is a mismatch. Using metal-silicate partition coefficients measured at low pressures and temperatures, it was found that the depletion is not as great as is expected (Fig. 2.13). For some elements the depletion is several orders of magnitude less than that expected after core formation. This problem, first noted by Ringwood (1966) for the elements Ni and Co, and subsequently extended to other siderophile elements, has become known as the "excess siderophile problem."... 

FIGURE 2.13 Chondrite normalized concentrations of siderophile elements in the Earth s mantle relative to those expected in the mantle if all the iron in the Earth s core had equilibrated with silicate at low pressures and temperature. The siderophile elements are arranged such that their siderophile nature increases from left to right (after Rama Murthy and Karato, 1997). 

Currently, the favored solution to the siderophile element problem, and the most popular model of core formation, is that silicate-metal equilibration took place at high pressures, in a deep magma ocean. Support for this model comes from very high pressure experimental studies of trace element partitioning, which show that metal-silicate partition... 

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