Non-chondritic platinum-group element ratios in oceanic mantle lithosphere; petrogenetic signature of melt percolation?

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doi: 10.1016/S0012-821X(99)00193-4
Authors:Rehkämper, Mark; Halliday, A. N.; Alt, J.; Fitton, J. G.; Zipfel, J.; Takazawa, E.
Author Affiliations:Primary:
University of Michigan, Department of Geological Sciences, Ann Arbor, MI, United States
Other:
University of Edinburgh, United Kingdom
Max-Planck-Institut für Chemie, Federal Republic of Germany
Niigata University, Japan
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 172(1-2), p.65-81. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1999
Note:In English. 50 refs.; illus., incl. 4 tables
Summary:The concentrations of the platinum-group elements (PGE) Ir, Ru, Pt and Pd were determined in 11 abyssal peridotites from ODP Sites 895 and 920, as well in six ultramafic rocks from the Horoman peridotite body, Japan, which is generally thought to represent former asthenospheric mantle. Individual oceanic peridotites from ODP drill cores are characterized by variable absolute and relative PGE abundances, but the average PGE concentrations of both ODP suites are very similar. This indicates that the distribution of the noble metals in the mantle is characterized by small-scale heterogeneity and large-scale homogeneity. The mean Ru/Ir and Pt/Ir ratios of all ODP peridotites are within 15% and 3%, respectively, of CI-chondritic values. These results are consistent with models that advocate that a late veneer of chondritic material provided the present PGE budget of the silicate Earth. The data are not reconcilable with the addition of a significant amount of differentiated outer core material to the upper mantle. Furthermore, the results of petrogenetic model calculations indicate that the addition of sulfides derived from percolating magmas may be responsible for the variable and generally suprachondritic Pd/Ir ratios observed in abyssal peridotites. Ultramafic rocks from the Horoman peridotite have PGE signatures distinct from abyssal peridotites: Pt/Ir and Pd/Ir are correlated with lithophile element concentrations such that the most fertile lherzolites are characterized by non-primitive PGE ratios. This indicates that processes more complex than simple in-situ melt extraction are required to produce the geochemical systematics, if the Horoman peridotite formed from asthenospheric mantle with chondritic relative PGE abundances. In this case, the PGE results can be explained by melt depletion accompanied or followed by mixing of depleted residues with sulfides, with or without the addition of basaltic melt. Abstract Copyright (1999) Elsevier, B.V.
Sections:Geochemistry
Subsections:Igneous rocks
Subjects:Chemical composition; Concentration; Cores; Crust; Dunite; Emplacement; Genesis; Geochemistry; Hydrology; Igneous rocks; Lithosphere; Major elements; Mantle; Metals; Models; Ocean Drilling Program; Oceanic crust; Percolation; Peridotites; Petrography; Platinum group; Plutonic rocks; Trace elements; Ultramafics; Asia; East Pacific; Equatorial Pacific; Far East; Hess Deep; Hokkaido; Horoman Complex; Japan; Leg 147; Leg 153; North Pacific; Northeast Pacific; ODP Site 895; ODP Site 920; Pacific Ocean
Coordinates:N021637 N021654 W1012645 W1012648
N232018 N232019 W0450102 W0450103
Abstract Numbers:00M/2937
Record ID:2000014024
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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