Figure F27. A. Site 1140 igneous rock compositions represented by total alkalis (Na₂O + K₂O) vs. SiO₂ (fields from Le Bas et al., 1986). All sampled lavas from Site 1140 are tholeiitic basalts. B. Alkalic and tholeiitic basalt fields are distinguished by the Macdonald-Katsura (1964) dashed line. Site 1140 basalts are poorer in alkalis than lavas from all other locations on the Kerguelen Plateau, except Site 750. The two samples that have slightly higher alkali contents correspond to lavas from Units 2 and 3. Compositions of basalts from southern and central Kerguelen Plateau locations are shown as fields for Sites 738, 747, 749, and 750 (Alibert, 1991; Mehl et al., 1991; Salters et al., 1992; Storey et al., 1992) and dredge samples (Davies et al., 1989; Weis et al., 1989). Open circles and diamond indicate highly altered samples from Sites 1137 and 1138, respectively.