Figure F61. A. Site 1138 igneous rock compositions represented by total alkalis (Na₂O + K₂O) vs. SiO₂. Unit 1 cobbles are dacites, whereas the pumice-rich portion of the Unit 2 breccia has a trachytic composition (large solid squares). Units 3-22 are tholeiitic to transitional basalts (diamonds). B. Alkalic and tholeiitic basalt fields are distinguished by the Macdonald-Katsura (1964) line. Site 1138 basalts are poorer in silica than those from Sites 1136 and 1137. Solid diamonds = upper series lavas; shaded diamonds = lower series lavas. Open symbols = samples determined from petrography and loss on ignition to have been affected by low-temperature alteration. Compositions for basalts from other southern and central Kerguelen Plateau locations are shown as fields for drilling Sites 738, 747, 749, and 750 and dredge locations reported by Davies et al. (1989) and Weis et al. (1989).