Figure 1. Map of the eastern Indian Ocean showing major physiographic features. Large black dots = DSDP and ODP drill sites, from which igneous basement was obtained on the Ninetyeast Ridge and Kerguelen Plateau; small black dots = dredge sites. Igneous basement was not obtained at ODP Sites 748 (gray shaded circle) and 752 (open circle).
Figure 2. Bathymetry of the Kerguelen Plateau (Fisher et al., pers. comm., 1996). Filled stars = previous ODP drill sites that recovered igneous basement; open stars = sites that bottomed in sediment. Closed circles = primary proposed drill sites (KIP) for Leg 183; open circles = alternate proposed drill sites. Seismic lines used to select the sites = black lines with cruise identifiers (GA = Gallieni; MD = Marion Dufresne; RS = rig seismic). Contour interval is 500 m.
Figure 3. Bathymetry of Broken Ridge (GEBCO, 1984). Filled stars = previous DSDP and ODP drill sites that recovered igneous basement; open stars = sites that bottomed in sediment. Black squares = dredge locations (DR-X) that recovered igneous basement. Open and closed circles = proposed drill sites (KIP-9B and 9C) for Leg 183 as in Figure 2. The seismic line used to select these sites = a black line with cruise identifier (C = Robert Conrad). Contour interval is 500 m.
Figure 4. Satellite-derived gravity field for the Kerguelen Plateau (Sandwell and Smith, 1997) showing important morphotectonic components of the plateau, location of previous ODP drill sites (black stars = sites where igneous basement was recovered), locations of the MD dredge sites (black squares) that recovered basaltic basement, and the proposed drill sites (KIP) for Leg 183. Bathymetric contours (1000 m interval) are from Fisher (pers. comm., 1996).
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. C. 208Pb/204Pb vs. 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 proposed field (Weis et al., 1993) for the plume is labeled "Southeast UMS." Data sources are as in Figure 5B.
To Table 1 : Primary Site Time Estimates
To 183 Table of Contents