Figure 13. Ti/Zr vs. MgO (in weight percent) for basalts from Broken Ridge and the Kerguelen Plateau. The four Kerguelen Plateau basement drill sites, 738, 747, 749, and 750 , have distinctive values ranging from unusually high to low ratios; the primitive mantle and norma l MORB ratios are 116 and 103, respectively (Sun and McDonough, 1989). Kerguelen Plateau basalts f rom Site 738, which have an obvious continental crustal component, also have anomalously low T i/Zr. Site 747 lavas also have relatively low Ti/Zr and high 87Sr/86Sr (Fig. 7). In many continental flood basalts, relatively low Ti/Zr results from contamination with continental crust. Abundances of Ti and Zr are precisely determined by the shipboard XRF analyses; therefore, Ti/Zr is a useful ratio for shipboard assessment of the role of continental crust in the Kerguelen Plateau and Broken Ridge basalts.

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Figure 13