Once subducted oceanic crustal material has been processed in the subduction zone environment (see the preceding paragraph), it is likely subducted into the deeper, convecting mantle as eclogite, the high-pressure form of basalt. Eventually this material may be incorporated into the mantle source regions of some erupted magmas. For example the geochemistry of some oceanic island basalts has been interpreted to suggest that discrete bodies of eclogite or pyroxenite in peridotite-dominated mantle, partially melted at high pressures and contributed to the lavas that erupted at the surface.
We are using techniques of high pressure experimental petrology and microbeam analysis of experimental products combined with studies of natural peridotite and eclogite samples from Norway, to investigate the conditions under which eclogite and pyroxenite partially melt in the upper mantle, the nature of the liquids they produce, and how these liquids would interact with and refertilise surrounding peridotite wall-rock. This will enable us to assess the importance of recycled crustal materials in genesis of basaltic and other magmas, and in the geochemical evolution of the earth.