Figure 31. Nb/Y vs. Zr/Y has been proposed as a discriminant for contamination of mantle plume derived melts, which fall within the two sloping, parallel lines defined by unco ntaminated basalts from the Iceland plume (Fitton et al., 1996). The Sun and McDonough (1989) primi tive mantle composition is located by the cross. Continental crustal material typically plot s to the right of the right line. Site 1138 basalt compositions are most similar to Site 747 compositions an d trend from the mantle array toward Site 1137 basalts (modest continental crustal assimilation). However, this trend most probably resulted from crystal fractionation of clinopyroxene.

To 183 Figure 32

To 183 Table of Contents

Figure 31