Primitive mantle siderophile elements

The two elements calcium and aluminum are RLEs. The assumption is usually made that aU RLEs are present in the primitive mantle of the Earth in chondritic proportions. Chondritic (undifferentiated) meteorites show significant variations in the absolute abundances of refractory elements but have, with few exceptions discussed below, the same relative abundances of lithophile and siderophile refractory elements. By analogy, the Earth s mantle abundances of refractory lithophile elements are assumed to occur in chondritic relative proportions in the primitive mantle, which is thus characterized by a single RLE/Mg ratio. This ratio is often normalized to the Cl-chondrite ratio and the resulting ratio, written as (RLE/Mg)N, is a measure of the concentration level of the refractory component in the Earth. A single factor of (RLE/Mg) valid for all RLEs is a basic assumption in this procedure and will be calculated from mass balance considerations. 

Spettel B., Palme H., and Wanke H. (1990) Siderophile elements in the primitive upper mantle. Lunar Planet. Sci. XXI. Lunar and Planetary Institute, Houston, pp. 1184-1185. 

A compositional model for the primitive mantle and bulk Earth is described above, which indirectly prescribes a core composition, although it does not identify the proportion of siderophile and chalcophile elements in the core and mantle. The mantle abundance pattern for the lithophile elements shown in Figure 4 provides a reference... 

The inclusion of the subjects covered in Volume 1 of this Treatise illustrates the recognition that one critical avenue to understanding geo chemistry is to understand the solar environment in which Earth formed. Chapter 2.01 of this volume compares the composition of Earth with that of various primitive meteorite classes and with the spectroscopically determined composition of the Sun. Chemical variability in these meteorites reflects primarily two processes (i) volatility and (u) affinity for metal (the so-called siderophile elements) over silicate (lithophile elements). Perhaps the most surprising outcome of this comparison is that Earth s mantle has a bulk composition that is close to solar, at least for refractory lithophile elements. As detailed in Chapter 2.01, the mantle s most obvious departures from solar composition are its deficiencies in volatile and siderophile elements. The latter is easily understood in that Earth has a large metallic core that extracted the missing siderophile elements from the mantle (Chapter 2.15). 

Siderophile element concentrations in the Earth s mantle are depleted relative to chondrites (Figs. 2.12 and 2.13), most probably as a consequence of metal-silicate equilibration during core formation. Os-isotope ratios ascribed to the PUM are also different from ratios found in primitive carbonaceous chondrites (Meisel et al., 2001), also possibly a consequence of core formation. 

Becker, H., Horan, M.R, Walker, R.J., Gao, S., Lorand, J.-P., and Rudnick, R.L., 2006. Highly siderophile element composition of the primitive upper mantle Constraints from new data on peridotite massifs and xenoliths. Geochim. Cosmochim. Acta, 70, 4528-50. 

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