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Figure F14. FeOT (Total Fe expressed as FeO) vs. MgO for the basement at Site 1256, compared with analyses of northern East Pacific Rise (EPR) (outline, Langmuir et al., 1986). Dashed lines show constant Mg#. Possible primary mantle melt compositions should have Mg# of 70–78 and MgO of 9–14 wt%. All flows and dikes, and most gabbros, are too evolved to be candidates for primary magmas.

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