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Platinum-group element contents of Karelian kimberlites : implications for the PGE budget of the sub-continental lithospheric mantle

Maier Wolfgang D., O'Brien Hugh, Peltonen Petri et Barnes Sarah-Jane. (2017). Platinum-group element contents of Karelian kimberlites : implications for the PGE budget of the sub-continental lithospheric mantle. Geochimica et Cosmochimica Acta, 216, p. 358-371.

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We present high-precision isotope dilution data for Os, Ir, Ru, Pt, Pd and Re in Group I and Group II kimberlites from the Karelian craton, as well as 2 samples of the Premier Group I kimberlite pipe from the Kaapvaal craton. The samples have, on average, 1.38 ppb Pt and 1.33 ppb Pd, with Pt/Pd around unity. These PGE levels are markedly lower, by as much as 80%, than those reported previously for kimberlites from South Africa, Brazil and India, but overlap with PGE results reported recently from Canadian kimberlites. Primitive-mantle-normalised chalcophile element patterns are relatively flat from Os to Pt, but Cu, Ni and, somewhat less so, Au are enriched relative to the PGE (e.g., Cu/Pd > 25.000). Pd/Ir ratios are 3,6 on average, lower than in most other mantle melts. The PGE systematics can be largely explained by two components, (i) harzburgite/lherzolite detritus of the SCLM with relatively high IPGE (Os-Ir-Ru)/PPGE (Rh-Pt-Pd) ratios, and (ii) a melt component that has high PPGE/IPGE ratios. By using the concentrations of iridium in the kimberlites as a proxy for the proportion of mantle detritus in the magma, we estimate that the analysed kimberlites contain 3–27% entrained and partially dissolved detritus from the sub-continental lithospheric mantle, consistent with previous estimates of kimberlites elsewhere (Tappe S. et al., 2016, Chem. Geol. The other major component in the samples is melt, modelled to contain an average of 0.85 ppb Pt and 1.09 ppb Pd. Assuming that Group II kimberlites are derived from relatively metasomatised SCLM, our data suggest that the metasomatised Karelian SCLM is relatively poor in Pt and Pd. If our data are representative of other Group II kimberlites elsewhere, this result could imply that the PGE enrichment in certain continental large igneous provinces, including Bushveld, is not derived from melting of metasomatised SCLM.

Type de document:Article publié dans une revue avec comité d'évaluation
Pages:p. 358-371
Version évaluée par les pairs:Oui
Date:1 Novembre 2017
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:Kimberlite, Platinum-group elements, Sub-continental lithospheric mantle, Finland, Karelian craton, Kaapvaal craton, Premier kimberlite pipe, Kaavi kimberlite, éléments du groupe du platine, manteau lithosphérique subcontinental, Finlande, craton du Carélie, craton du Kaapvaal, pipe de kimberlite de Premier, kimberlite de Kaavi
Déposé le:16 nov. 2017 22:49
Dernière modification:10 févr. 2023 21:32
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