Figure F33. Nb/Y vs. Zr/Y diagram. This plot has been used to distinguish lavas derived from the Icelandic mantle plume from North Atlantic mid-ocean-ridge basalt (MORB) (Fitton et al., 1998). Shown for comparison are data for other Leg 183 sites and fields for basalts from Sites 738, 747, 749 and 750. Primitive mantle (PM) composition is located by the cross, and average oceanic island basalt (OIB) and MORB compositions are indicated by a black dot (data from Sun and McDonough, 1989). Site 1140 basalts plot within the plume-derived field. Units 1, 5, and 6 define a field that overlaps with Site 749 basalts, whereas Units 2 and 3 have higher ratios, comparable to those of Sites 1138 and 747 basalts. Data sources are the same as in Figure F27.