Figure F27. Zr/Ti, Nb/Zr, and Nb/Ce ratios vs. Zr/Y ratio or Zr content. These ratios are sensitive to the presence of a component from the continental crust and have been normalized to primitive mantle values. Note that basalts from Site 738, which are thought to contain a continental component (Mahoney et al., 1995), have the lowest Nb/Ce and Nb/Zr and highest Zr/Ti values. Basalts from Site 1136 most closely resemble the upper compositional group from Site 749. Subscript "N" indicates that ratios are normalized to primitive mantle abundances of Sun and McDonough (1989). Open symbols = samples from Unit 1; solid symbols = samples from Unit 2; circles = fresh samples; open square = Sample 183-1136A-15R-2 (Piece 2, 69-71 cm) (altered basalt); solid square = Sample 183-1136A-18R-4 (Piece 2, 89-92 cm) (vesicle-rich segregation). Data sources are Davies et al. (1989), Weis et al. (1989), Alibert (1991), Mehl et al. (1991), Salters et al. (1992), Storey et al. (1992), and Mahoney et al. (1995).