Figure F4. SiO2 vs. K2O. The line at 0.2 wt% K2O is a lower boundary of enriched mid-ocean-ridge basalt (E-MORB) (Cushman et al., 2004). Open diamond = normal mid-ocean-ridge basalt as average basaltic glass from Atlantic, Pacific, and Indian Ocean spreading centers, open square = E-MORB as average basalt from vicinity of Galapagos hotspot on the Galapagos spreading axis (from table 8-1 in McBirney, 1993).

Figure F4. SiO₂ vs. K₂O. The line at 0.2 wt% K₂O is a lower boundary of enriched mid-ocean-ridge basalt (E-MORB) (Cushman et al., 2004). Open diamond = normal mid-ocean-ridge basalt as average basaltic glass from Atlantic, Pacific, and Indian Ocean spreading centers, open square = E-MORB as average basalt from vicinity of Galapagos hotspot on the Galapagos spreading axis (from table 8-1 in McBirney, 1993).