Nature 379, 712 - 715 (22 February 1996); doi:10.1038/379712a0

Non-chondritic platinum-group element ratios in the Earth's mantle

L. Pattou, J. P. Lorand & M. Gros

Laboratoire de Minéralogie, Muséum National d'Histoire Naturelle, Unité Associée au CNRS 736, 61 Rue Buffon, 75005 Paris, France

THE Earth's upper mantle has an overabundance of highly siderophile elements (platinum-group elements, gold and rhenium), relative to what would be expected from equilibrium with the metallic core^1–3. This excess is now widely believed to have been introduced as a "late veneer" by meteorite bombardment during early Earth history, but after separation of the core⁴. Here we report high-precision analyses of platinum-group elements (PGEs) from fertile upper-mantle Iherzolites, which show variations in relative abundances that exceed those in the chondritic meteorites that are thought to have furnished the late veneer⁵. In particular, the Pd/Ir ratio, at about 1.76, is significantly greater than that of known chondritic meteorites⁶. Our results, combined with previous indications of both non-chondritic and nearly chondritic PGE ratios in the few other fertile mantle Iherzolites that have been analysed^2,3,7–11, strongly suggest that the mantle is heterogeneous in its PGE content on scales of 100 kilometres. If the observed PGE ratios can be reconciled with a plausible meteoritic source, the observed heterogeneity may reflect an original spatial variation in the late veneer; otherwise, an additional fractionation mechanism seems to be required.

References

1.	Jagoutz, E., et al. Proc. lunar planet. Sci. Conf. X, 2031−2050 (1979).
2.	Mitchell, R. H. & Keays, R. R. Geochim. cosmochim. Acta 45, 2425−2445 (1981). | Article | ISI | ChemPort |
3.	Morgan, J. W., Wandless, G. A., Petrie, R. K. & Irving, A. J. Tectonophysics 75, 47−67 (1981). | Article | ISI | ChemPort |
4.	Kimura, K., Lewis, R. S. & Anders, E. Geochim. cosmochim. Acta 38, 683−701 (1974). | Article | ISI | ChemPort |
5.	Morgan, J. W. J. geophys. Rev. 91, 12375−12387 (1986).
6.	Wasson, J. T. & Kallemeyn, G. W. Phil. Trans. R. Soc. Lond. A 325, 533−544 (1988).
7.	Hamlyn, P. H., Keays, R. R., Cameron, W. E., Crawford, A. J. & Waldron, H. M. Geochim. cosmochim. Acta 49, 1797−1811 (1985). | Article | ChemPort |
8.	Barnes, S. J., Naldrett, A. J. & Gorton, M. P. Chem. Geol. 53, 303−323 (1985). | Article | ChemPort |
9.	Garuti, G., Gorgoni, C. & Sighinolfi, G. P. Earth. planet. Sci. Lett. 70, 69−87 (1984). | Article | ChemPort |
10.	Page, N. J. & Talkington, R. W. Can. Mineral. 22, 137−149 (1984). | ChemPort |
11.	Govindaraju, M. Geostandard Newsletter (spec. iss.) VIII, July (1984).
12.	Spettel, B., Palme, H., Ionov, D. A. & Kogarko, L. N. Lunar planet. Sci. XXII, 1301−1302 (1991).
13.	Greenough, J. D. & Fryer, B. J. Proc. ODP Sci. Res. 115, 71−84 (1990).
14.	Dowling, S. E. & Hill, R. E. T. Aust. J. Earth Sci. 39, 349−363 (1992).
15.	Brügmann, G. et al. Geochim. cosmochim. Acta 57, 2001−2018 (1993).
16.	Barnes, S. J. & Picard, C. P. Geochim. cosmochim. Acta 57, 79−87 (1993). | Article | ChemPort |
17.	Fabriès, J., Lorand, J. P., Bodinier, J. L. & Dupuy, C. J. Petrology (spec. Iherzolite iss.) 55−76 (1991).
18.	Downes, H., Bodinier, J. L., Thirswall, M. F., Lorand, J. P. & Fabriès, J. J. Petrology (spec. Iherzolite iss.) 97−115 (1991).
19.	Bodinier, J. L., Dupuy, C. & Dostal, J. Geochim. cosmochim. Acta 52, 2893−2907 (1988). | Article | ChemPort |
20.	Reisberg, L. & Lorand, J. P. Nature 376, 159−162 (1995). | Article | ISI | ChemPort |
21.	Lorand, J. P., Bodinier, J. L., Dupuy, C. & Dostal, J. Geochim. cosmochim. Acta 53, 3085−3090 (1989). | Article | ChemPort |
22.	Barnes, S. J. & Francis, D. Econ. Geol. 90, 135−154 (1995). | ChemPort |
23.	Hall, G. E. M. & Pelchat, J. C. Chem. Geol. 115, 61−72 (1994). | Article | ChemPort |
24.	Keays, R. R. Lithos 34, 1−19 (1995). | Article | ChemPort |
25.	McDonougn, W. F. Lunar planet Sci. XXVI, 927−928 (1995).
26.	Hart, S. & Zindler, A. Chem. Geol. 57, 247−267 (1986). | Article | ChemPort |
27.	Lorand, J. P., Keays, R. R. & Bodinier, J. L. J. Petrology 34, 1111−1140 (1993). | ChemPort |
28.	Borisov, A., Palme, H. & Spettel, B. Geochim. cosmochim. Acta 58 705−716 (1994). | Article | ISI | ChemPort |
29.	Borisov, A. & Palme, H. Geochim. cosmochim. Acta 59, 481−487 (1995). | Article | ISI | ChemPort |
30.	Morgan, J. W., Walker, R. J. & Horan, M. F. Paper presented at Workshop on the Formation of the Earth's Core Mainz, 18−20 (April 1994).
31.	Hertogen, J., Janssens, M. J., Takahashi, H. & Anders, E. Geochim. cosmochim. Acta 47, 2241−2255 (1983). | Article | ISI | ChemPort |
32.	Morgan, J. W., Janssens, M. J., Takahashi, H., Hertogen, J. & Anders, E. J. Geochim. cosmochim. Acta 49, 247−259 (1985). | Article | ISI | ChemPort |
33.	Shirey, S. B. Mineralog. Mag. 58A, 833−844 (1994).
34.	Lorand, J. P. Earth planet. Sci. Lett. 93, 50−64 (1989). | Article | ChemPort |
35.	Anders, E. & Grevesse, N. Geochim. cosmochim. Acta 49, 197−214 (1989).