Figure F18. Total alkali content (Na2O + K2O) vs. SiO2 classification plot for lava flows from Nintoku Seamount. The solid diagonal line is the alkalic-tholeiitic dividing line for Hawaiian basalt (Macdonald and Katsura, 1964). Only two lava units (Subunits 18b and 19b) at Site 1205 are composed of tholeiitic basalt. All other flow units at Site 1205 and nearby DSDP Site 432 (data from Kirkpatrick et al., 1980; M. Regelous et al., unpubl. data) are alkalic basalt. At both sites, conglomerates overlying igneous basement contain hawaiite clasts, which are distinguished by their high total alkali (>6 wt%) and relatively high SiO2 content. Shown for comparison are data for Suiko Seamount (Site 433), which is dominantly tholeiitic basalt (Kirkpatrick et al., 1980; M. Regelous et al., unpubl. data).

Figure F18. Total alkali content (Na₂O + K₂O) vs. SiO₂ classification plot for lava flows from Nintoku Seamount. The solid diagonal line is the alkalic-tholeiitic dividing line for Hawaiian basalt (Macdonald and Katsura, 1964). Only two lava units (Subunits 18b and 19b) at Site 1205 are composed of tholeiitic basalt. All other flow units at Site 1205 and nearby DSDP Site 432 (data from Kirkpatrick et al., 1980; M. Regelous et al., unpubl. data) are alkalic basalt. At both sites, conglomerates overlying igneous basement contain hawaiite clasts, which are distinguished by their high total alkali (>6 wt%) and relatively high SiO₂ content. Shown for comparison are data for Suiko Seamount (Site 433), which is dominantly tholeiitic basalt (Kirkpatrick et al., 1980; M. Regelous et al., unpubl. data).