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 Hole U1309B and basalts and diabases from Hole U1309D. A compilation of the compositions of Mid-Atlantic Ridge glasses (open diamonds) downloaded from PetDB in December 2004 (online at beta.www.petdb.org) is shown for comparison. The continuous line represents the alkalic-tholeiitic boundary of Irvine and Baragar (1971). Ol = olivine.

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