Leg 183

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. The above basement lavas from ODP Site 748 are alkalic basalts. 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 post-magmatic alteration. As an extreme example, the solid triangle indicates 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 ODP Site 738. Data from Davies et al. (1989), Storey et al. (1992), and Mahoney et al. (1995).

(B) 143Nd/144Nd versus 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 ODP 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, and Ninetyeast Ridge (NER and NER DSDP Site 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.

(C) 208Pb/204Pb versus 206Pb/204Pb showing measured data points for basalts recovered from the Kerguelen Plateau and Broken Ridge. Shown for comparison are measured fields for SEIR MORB and lavas from St. Paul and Amsterdam Islands and initial ratios for lavas from the Kerguelen Archipelago and the Ninetyeast Ridge. The propoed field (Weis et al., 1993) for the plume is labeled "Southeast UMS." Data sources are as in Figure 5B.

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