Figure F15. Total alkalis, Na2O + K2O, versus SiO2 (after Le Maitre et al., 1989). Data are plotted on a volatile-free basis for basalts, diabases, and basalt breccia from Holes U1309B and U1309D. Compilation of the compositions of Mid-Atlantic Ridge (MAR) glasses (PetDB, December 2004; www.petdb.org) is shown for comparison. The continuous line represents the alkalic/tholeiitic boundary of Irvine and Baragar (1971). Ol = normative olivine, Q = normative quartz.
Previous | Close | Next | Top of page