Journal of Petrology | Volume 40 | Number 11 | Pages 1721-1744 | 1999
© Oxford University Press 1999
Evolution of Heterogeneous Lithospheric Mantle in a Plume Environment Beneath the Kerguelen Archipelago
1 DéPartement Des Sciences De La Terre Et De L'environnement, Université Libre De Bruxelles CP 160/02, AV. F. D. Roosevelt 50, B-1050 Brussels, Belgium
2 Geology and Geophysics, Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA
3 Laboratoire de GÉOLOGIE–CNRS UA10, Université Jean Monnet CNRS–UMR 6524, F- 42023 Saint-Etienne, France
Received October 1, 1998; Revised typescript accepted May 21, 1999
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Abstract |
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A combined petrographic, geochemical and Sr–Nd–Pb isotopic investigation of peridotite xenoliths from the Kerguelen Archipelago (southern Indian Ocean) provides new insights into melt migration mechanisms and the sources of heterogeneities in the mantle associated with the long-lived (
115 my) Kerguelen mantle plume. Large variations of trace element concentrations in clinopyroxenes and their isotopic compositions reflect the strong imprint of complex, multi-stage metasomatic episodes during evolution of the lithospheric mantle under the Kerguelen Archipelago. Two metasomatic agents have been identified that have interacted with the mantle peridotite matrix: (1) a basaltic melt, and (2) a carbonatitic melt that produced extremely high and variable incompatible element abundances in clinopyroxenes, which are attributed to chromatographic effects associated with metasomatic melt transport by porous flow through the mantle. Isotopic compositions of 12 peridotite xenoliths indicate that both types of metasomatic melts are related to the alkaline magmatism produced by the Kerguelen plume. In contrast, isotopic data from a single dunite xenolith indicate the strong influence of a continental lithospheric component, probably derived from Gondwanaland, that either forms part of the Kerguelen Plateau or was incorporated into the mantle beneath Kerguelen and mixed with plume-derivedmaterial. Our geochemical study of Kerguelen xenoliths testifiesto the importance of plumes as mechanisms for producing metasomatic melts with highly variable compositions and for entraining different components that may act as contaminants for eruptedlavas.
KEY WORDS: geochemistry; isotopes; Kerguelen plume; mantle chromatography; metasomatized xenoliths
* Corresponding author. Telephone: +32-2-650-22-69. Fax: +32-2-650-22-26. e-mail: nmattiel{at}ulb.ac.be
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