Figure 25. Nb/Y vs. Zr/Y diagram for Kerguelen Plateau basement basalt from Sites 738, 747, 749, 750, 1136, and 1137. The diagonal lines delimit the field of plume-derived Icela ndic lavas; MORB plots to the right of this field. Fitton et al. (1998) argue that melts derived by a varying extent of melting from a common peridotite source define trajectories nearly parallel to t hese boundary lines. Average MORB and oceanic island basalt (OIB) (Sun and Mc Donough, 1989), average lower and upper crust (LCC and UCC, respectively, Rudnick and Fountain, 1995), alkalic bas alts from Site 748 (recovered above basement), and the evolved rocks from Site 1137 are shown for r eference.

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Figure 25