Platinum-group element abundance patterns in different mantle environments

Science

Volumn 278, Issue 5343, 1997, Pages 1595-1598

  Rehkämper, Mark ^a   Halliday, Alex N ^a   Barfod, Dan ^a   Fitton, J Godfrey ^b   Dawson, J Barry ^b  

^a UNIVERSITY OF MICHIGAN   (United States)

^b UNIVERSITY OF EDINBURGH   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

PLATINUM;

LHENZOLOITE; LITHOSPHERE; PERIDOTITE; PGE; UPPER MANTLE; ZENOLITH;

ANALYTIC METHOD; ARTICLE; CAMEROON; ENVIRONMENT; GEOLOGY; PRIORITY JOURNAL; ROCK; SURFACE PROPERTY; TANZANIA;

CAMEROON; TANZANIA;

EID: 0037674444     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.278.5343.1595     Document Type: Article

References (65)

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47. Spinels from fertile western Australian Iherzolites, for example, are characterized by superchondritic Pd/Ir ratios (2), as are chromitites from stratiform chromite deposits [C. McLaren and J. P. R. De Villiers, Econ. Geol. 77, 1348 (1982); S. J. Perry, Chem. Geol. 43, 115 (1984)]. Furthermore, a large proportion of the PGE budget of fertile peridotite xenoliths appears to be contained in acid-leachable, intergranular sulfide phases, whereas spinel is only a minor host for the PGEs (2) [S. R. Hart and G. E. Ravizza, in Earth Processes: Reading the Isotopic Code, A. Basu and S. R. Hart, Eds. (American Geophysical Union, Washington, DC, 1996), pp. 123-134]. Although chromitites from ophiolite complexes are characterized by high PGE abundances, a number of detailed studies demonstrate that the PGEs are not incorporated into the lattice of the chromites but are concentrated in sulfide and alloy inclusions; the chromites themselves have no bearing on the fractionation of the PGEs [for example, H. W. Stockmann and P. F. Hlava, Econ. Geol. 79, 491 (1984); R. W. Talkington, D. H. Watkinson, P. J. Whittaker, P. C. Jones, Tschermaks Mineral. Petrogr. Mitt. 32, 285 (1984); R. J. Walker, E. Hanski, J. Vuollo, J. Liipo, Earth Planet. Sci. Lett. 141, 161 (1996)].
48. Spinels from fertile western Australian Iherzolites, for example, are characterized by superchondritic Pd/Ir ratios (2), as are chromitites from stratiform chromite deposits [C. McLaren and J. P. R. De Villiers, Econ. Geol. 77, 1348 (1982); S. J. Perry, Chem. Geol. 43, 115 (1984)]. Furthermore, a large proportion of the PGE budget of fertile peridotite xenoliths appears to be contained in acid-leachable, intergranular sulfide phases, whereas spinel is only a minor host for the PGEs (2) [S. R. Hart and G. E. Ravizza, in Earth Processes: Reading the Isotopic Code, A. Basu and S. R. Hart, Eds. (American Geophysical Union, Washington, DC, 1996), pp. 123-134]. Although chromitites from ophiolite complexes are characterized by high PGE abundances, a number of detailed studies demonstrate that the PGEs are not incorporated into the lattice of the chromites but are concentrated in sulfide and alloy inclusions; the chromites themselves have no bearing on the fractionation of the PGEs [for example, H. W. Stockmann and P. F. Hlava, Econ. Geol. 79, 491 (1984); R. W. Talkington, D. H. Watkinson, P. J. Whittaker, P. C. Jones, Tschermaks Mineral. Petrogr. Mitt. 32, 285 (1984); R. J. Walker, E. Hanski, J. Vuollo, J. Liipo, Earth Planet. Sci. Lett. 141, 161 (1996)].
49. Spinels from fertile western Australian Iherzolites, for example, are characterized by superchondritic Pd/Ir ratios (2), as are chromitites from stratiform chromite deposits [C. McLaren and J. P. R. De Villiers, Econ. Geol. 77, 1348 (1982); S. J. Perry, Chem. Geol. 43, 115 (1984)]. Furthermore, a large proportion of the PGE budget of fertile peridotite xenoliths appears to be contained in acid-leachable, intergranular sulfide phases, whereas spinel is only a minor host for the PGEs (2) [S. R. Hart and G. E. Ravizza, in Earth Processes: Reading the Isotopic Code, A. Basu and S. R. Hart, Eds. (American Geophysical Union, Washington, DC, 1996), pp. 123-134]. Although chromitites from ophiolite complexes are characterized by high PGE abundances, a number of detailed studies demonstrate that the PGEs are not incorporated into the lattice of the chromites but are concentrated in sulfide and alloy inclusions; the chromites themselves have no bearing on the fractionation of the PGEs [for example, H. W. Stockmann and P. F. Hlava, Econ. Geol. 79, 491 (1984); R. W. Talkington, D. H. Watkinson, P. J. Whittaker, P. C. Jones, Tschermaks Mineral. Petrogr. Mitt. 32, 285 (1984); R. J. Walker, E. Hanski, J. Vuollo, J. Liipo, Earth Planet. Sci. Lett. 141, 161 (1996)].
50. Spinels from fertile western Australian Iherzolites, for example, are characterized by superchondritic Pd/Ir ratios (2), as are chromitites from stratiform chromite deposits [C. McLaren and J. P. R. De Villiers, Econ. Geol. 77, 1348 (1982); S. J. Perry, Chem. Geol. 43, 115 (1984)]. Furthermore, a large proportion of the PGE budget of fertile peridotite xenoliths appears to be contained in acid-leachable, intergranular sulfide phases, whereas spinel is only a minor host for the PGEs (2) [S. R. Hart and G. E. Ravizza, in Earth Processes: Reading the Isotopic Code, A. Basu and S. R. Hart, Eds. (American Geophysical Union, Washington, DC, 1996), pp. 123-134]. Although chromitites from ophiolite complexes are characterized by high PGE abundances, a number of detailed studies demonstrate that the PGEs are not incorporated into the lattice of the chromites but are concentrated in sulfide and alloy inclusions; the chromites themselves have no bearing on the fractionation of the PGEs [for example, H. W. Stockmann and P. F. Hlava, Econ. Geol. 79, 491 (1984); R. W. Talkington, D. H. Watkinson, P. J. Whittaker, P. C. Jones, Tschermaks Mineral. Petrogr. Mitt. 32, 285 (1984); R. J. Walker, E. Hanski, J. Vuollo, J. Liipo, Earth Planet. Sci. Lett. 141, 161 (1996)].
51. Spinels from fertile western Australian Iherzolites, for example, are characterized by superchondritic Pd/Ir ratios (2), as are chromitites from stratiform chromite deposits [C. McLaren and J. P. R. De Villiers, Econ. Geol. 77, 1348 (1982); S. J. Perry, Chem. Geol. 43, 115 (1984)]. Furthermore, a large proportion of the PGE budget of fertile peridotite xenoliths appears to be contained in acid-leachable, intergranular sulfide phases, whereas spinel is only a minor host for the PGEs (2) [S. R. Hart and G. E. Ravizza, in Earth Processes: Reading the Isotopic Code, A. Basu and S. R. Hart, Eds. (American Geophysical Union, Washington, DC, 1996), pp. 123-134]. Although chromitites from ophiolite complexes are characterized by high PGE abundances, a number of detailed studies demonstrate that the PGEs are not incorporated into the lattice of the chromites but are concentrated in sulfide and alloy inclusions; the chromites themselves have no bearing on the fractionation of the PGEs [for example, H. W. Stockmann and P. F. Hlava, Econ. Geol. 79, 491 (1984); R. W. Talkington, D. H. Watkinson, P. J. Whittaker, P. C. Jones, Tschermaks Mineral. Petrogr. Mitt. 32, 285 (1984); R. J. Walker, E. Hanski, J. Vuollo, J. Liipo, Earth Planet. Sci. Lett. 141, 161 (1996)].
52. Three abyssal harzburgites from the MARK area (Mid-Atlantic Ridge, Kane Fracture Zone) with <1.0% CaO are characterized by suprachondritic Pd/Ir ratios and Pt/Ru ratios that are only marginally subchondritic (M. Rehkämper et al., in preparation). Two harzburgites from the Horomann peridotite (CaO < 0.5%), generally considered to represent former suboceanic mantle lithosphere, have Pd/Ir ratios of 0.15 to 0.20 but higher-than-chondritic ratios of Pt/Ir and R/Ru (E. Takazawa, thesis, MIT (1996); M. Rehkämper et al., in preparation]. These characteristics are remarkably similar to the results for harzburgite sample N12 from the Cameroon Line (this study). Six harzburgites and dunites from the Ronda and Beni Bousera massifs with 0.3 to 1% CaO display a wide range of Pd/Ir ratios (0.24 to 1.44) and R/Ru ratios (0.31 to 2.40) (6). These values are significantly larger, by at least a factor of 5, than the minimum ratios recorded for the northern Tanzanian xenoliths.
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65. We thank M. Johnson, D.-C. Lee, J. Christensen, C. Hall, D. Teagle, and the other members of the RIGL team for help in keeping the P54 running smoothly and for many fruitful discussions; C. Paslick for field assistance; D. Bugocki and W. Yi for vital assistance during sample preparation; and S. Mukasa and J. Zipfel for helpful comments. Three anonymous referees provided very thorough and helpful reviews. This research was supported by NSF grants EAR 94-06248 and EAR 96-14457 and by DOE grant DE-FG02-94ER14412.