Evolution of heterogeneous lithospheric mantle in a plume environment beneath the Kerguelen Archipelago

A combined petrographic, geochemical and Sr-Nd-Pb, isotopic investigation o f peridotite xenoliths from the Kerguelen Archipelago (southern Indian Ocea n) provides new insights into melt migration mechanisms and the sources of heterogeneities in the mantle associated with the long-lived (similar to 11 5 my) Kerguelen mantle plume. Large variations of trace element concentrati ons in clinopyroxenes and their isotopic compositions reflect the strong im print of complex, multistage metasomatic episodes during evolution of the l ithospheric 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 an attributed to chromatographic effects associated with metasomatic melt t ransport by porous flow through the mantle. Isotopic compositions of 12 per idotite xenoliths indicate that both types of metasomatic melts are related to the alkaline magmatism produced by the Kerguelen plume. In contrast, is otopic data from a single dunite xenolith indicate the strong influence of a continental lithospheric component, probably derived from Gondwanaland, t hat either forms part of the Kerguelen Plateau or was incorporated into rit e mantle beneath Kerguelen and mixed with plume-derived material. Our geoch emical study of Kerguelen xenoliths testifies to the importance of plumes a s mechanisms for producing metasomatic melts with highly variable compositi ons and for entraining different components that may act as contaminants fo r erupted lavas.