Figure F25. Nb/Y vs. Zr/Y for Kerguelen Plateau basement basalt from Sites 738, 747, 749, 750, 1136, and 1137. The two diagonal lines delimit the field of plume-derived Icelandic lavas; MORB plots to the right of this field as do plume-derived basalts that have been contaminated by upper continental crust. Fitton et al. (1997) argue that melts derived by a varying extent of melting from a common peridotite source define trajectories nearly parallel to these boundary lines. Average MORB and oceanic island basalt (OIB) (Sun and McDonough, 1989), average lower and upper continental crust (LCC and UCC, respectively, Rudnick and Fountain, 1995), alkalic basalts from Site 748 (recovered above basement), and the evolved rocks from Site 1137 are shown for reference.