Siderophile elements temperature

Iron oxides present in coal are generally stable for the relatively short period of time that they are exposed to combustion temperatures. Therefore, siderophile elements (e.g., Ni, Co, Mo, Pt, Pd, Au) that are incorporated within iron oxides are also expected to remain stable, and escape any significant thermal transformation reactions (Bums 2003). Similarly, lithophile elements (e.g., Ba, B, Cr, Mn, Sr, V) that are initially found in association with silicates and aluminosilicates in coal are expected to be incorporated within the glassy fraction of coal ash upon thermal transformation of their parent minerals (Bums 2003). 

Two different kinds of metals are found in chondrites. Small nuggets composed of highly refractory siderophile elements (iridium, osmium, ruthenium, molybdenum, tungsten, rhenium) occur within CAIs. These refractory alloys are predicted to condense at temperatures above 1600 from a gas of solar composition. Except for tungsten, they are also the expected residues of CAI oxidation. 

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. 

Figure 1 The estimated composition of the silicate portion of the Earth as a function of condensation temperature normalized to Cl values in Anders and Grevesse (1989). Open circles lithophile elements shaded squares chalcophile elements shaded triangles moderately siderophile elements solid diamonds highly siderophile elements. The spread in concentration for a given temperature is thought to be due to core formation. The highly siderophile element abundances may reflect a volatile depleted late veneer. Condensation temperatures are from Newsom (1995).

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). 

The refractory component comprises the elements with the highest condensation temperatures. There are two groups of refractory elements the refractory lithophile elements (RLEs)—aluminum, calcium, titanium, beryllium, scandium, vanadium, strontium, yttrium, zirconium, niobium, barium, REE, hafnium, tantalum, thorium, uranium, plutonium—and the refractory siderophile elements (RSEs)—molybdenum, ruthenium, rhodium, tungsten, rhenium, iridium, platinum, osmium. The refractory component accounts for —5% of the total condensible matter. Variations in refractory element abundances of bulk meteorites reflect the incorporation of variable fractions of a refractory aluminum, calcium-rich component. Ratios among refractory lithophile elements are constant in all types of chondritic meteorites, at least to within —5%. 

Figure 15 Abundances of moderately volatile elements in the Earth s mantle versus condensation temperatures (a) lithophile elements define the volatility trend (b) siderophile elements have variable depletions reflecting the process of core formation and (c) chalcophile elements. The difference between siderophile and chalcophile elements is not well defined, except for S and Se. The large depletions of S, Se, and Te are noteworthy (see text) (after...

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. 

Capobianco C. J., Jones J. H., and Drake M. J. (1993) Metal/ silicate thermochemistry at high temperature magma oceans and the excess siderophile element problem of the Earth s Upper Mantle. J. Geophys. Res. 98, 5433-5443. 

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... 

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