Figure F68. Nb/Y vs. Zr/Y has been proposed as a discriminant between MORB and mantle plume-derived melts. In Iceland, plume-derived melts fall within the two sloping, parallel lines (Fitton et al., 1997, 1998). Fields for compositions from other southern and central Kerguelen Plateau drilling sites are discussed in Figure F32 in the "Leg 183 Summary" chapter. The Sun and McDonough (1989) primitive mantle composition is represented by the cross. Continental crustal material typically plots to the right of the plume field. Site 1138 basalt compositions are most similar to those from Site 747 and trend from the mantle array toward Site 1137 basalt compositions, which may contain a continental crust component (see "Igneous Petrology" in the "Site 1137" chapter). However, the Site 1138 basalts may reflect crystal fractionation of clinopyroxene.