Figure 5. A. Total alkalis vs. SiO₂ plot (wt% with FeO adjusted to 85% of total iron) for classifying tholeiitic and alkalic basalts. Lavas from Kerguelen Plateau ODP Sites 747, 749, and 750 are tholeiitic basalts. Lavas from ODP Site 748 are alkalic basalts that were recovered 200 m above basement. The lavas dredged from the central Kerguelen Plateau (open circles) and ODP Site 738 straddle the boundary line, largely because the alkali contents of these lavas were increased during postmagmatic alteration. As an extreme example, the solid triangle = a highly altered sample (Hole 750B-19R-1, 47-50 cm) from ODP Site 750. Lavas from Dredges 9 and 10 on Broken Ridge are also tholeiitic, whereas lavas from Dredge 8 overlap with the field for Site 738. Data from Davies et al. (1989), Storey et al. (1992), and Mahoney et al. (1995). B. ¹⁴³Nd/¹⁴⁴Nd vs. ⁸⁷Sr/⁸⁶Sr showing data points for basalts recovered from the Kerguelen Plateau and Broken Ridge. The Broken Ridge samples are measured data corrected to an eruption age of 88 Ma, the dredged Kerguelen Plateau samples are measured data corrected to an eruption age of 115 Ma. The effects of age correction are shown by the two fields (measured and age corrected) for Site 738 on the southern Kerguelen Plateau. Data for other ODP sites are not age corrected because parent/daughter abundance ratios are not available. Data for Kerguelen Plateau and Broken Ridge samples are from Weis et al. (1989), Salters et al. (1992), and Mahoney et al. (1995). Shown for comparison are fields for SEIR MORB, St. Paul and Heard Islands (Heard data = trajectory of solid line from Barling et al., 1994), and Ninetyeast Ridge (gray-shaded fields labeled NER and NER 216), the entire Kerguelen Archipelago with subfields indicated for the youngest archipelago lavas (Mt. Ross and Southeast UMS), which Weis et al. (1993, 1997) interpret as representative of the Kerguelen Plume

To Figure 5 continued

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