Figure 13. Plot of Nb vs. relative depth for basalts recovered from the 63ºN transect, Southeast Greenland margin, during Legs 152 and 163. Nb reflects the excess or deficiency of Nb, using the lower bound of the Iceland array (Fig. 12) as a reference line: Nb = 1.74 + log(Nb/Y) - 1.92 · log(Zr/Y) (Fitton et al., 1997). Uncontaminated samples with a negative value for Nb imply a derivation from the depleted (MORB) upper mantle, whereas samples with positive Nb imply a derivation from an Icelandic mantle source. Depth scale is relative (e.g., the Site 917 Middle Series is omitted, as are the gaps between the different sites, and the basalts from Site 990 may be younger than those from Site 989). Data sources for Leg 163 are this paper and Larsen et al. (Chap. 7, this volume); Leg 152, Fitton et al. (1998b).