Platinum group elements fractionation

Capobianco, C.H. Drake, M. 1990. Partitioning of ruthenium, rhodium, and palladium between spinel and silicate melt and implications for platinum-group element fractionation trends, Geochimica et Cosmochimica Acta, 54, 869-874. 

Pearson D. G., Irvine G. J., Ionov D. A., Boyd F. R., and Dreibus G. E. (2004) Re-Os isotope systematics and platinum group element fractionation during mantle melt extraction a study of massif and xenolith peridotite suites. Chem. Geol. (special volume) Highley Siderophile Elements (in press). 

Fig. 7. Platinum group element fractions (Pd/Ir)n v. bulk-rock AI2O3 for selected cratonic and circum-cratonic peridotites. Also plotted are the two melt-depletion curves from Fig. 3. It should be noted that some peridotites from Table 1 plot close to the theoretical melting trends (FRB1181 40-21) or on an extension of the trends, at very low Pd/Ir, following complete removal of sulphide. These samples have Tro and Tma ages in reasonably close agreement. Other samples are dispersed away from the trends (see text for details).

Chen, J. H., Papanastassiou, D.A. and Wasserburg, G. J. (1998) Re-Os systematics in chondrites and the fractionation of the platinum group elements in the early solar system. Geochimica et Cosmochimica Acta, 62, 3379—3392. 

Lorand J.-P., Patton L., and Gros M. (1999) Fractionation of platinum-group elements and gold in the upper mantle a detailed smdy in Pyrenean orogenic Iherzohtes. J. Petrol. 40, 957-981. 

Fleet, M. E., and W. E. Stone, Partitioning of platinum-group elements in the Fe-Ni-S system and their fractionation in nature, Geochim. Cosmochim. Acta, 55, 245-253, 1991. 

Figure 7.7 Cause-effect or fishbone diagram for the isotope dilution determination of the mass fraction of a platinum group element (Os) in geological reference materials [7]. The most important influence quantities are marked with a box. It takes into account natural variations in the Os/ Os ratio, which can contribute significantly to the total uncertainty in the Os concentration. R represents the isotope ratio (the artificially enriched isotope divided by the isotope used for normalization) for the blend (B), the spike (y) and the naturally occurring element (x). Masses of sample and spike are represented by m and are expressed in grams. and ZR,, are the sum of all isotope ratios for the spike and the sample, respectively k represents the amount contents in mol g .

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%. 

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... 

---