Figure 12. Downhole variation for MgO (A) and Zr (B), demonstrating the magmatic trends of increasing MgO and decreasing Zr toward more primitive liquids upsection. In addition, smaller scale variation is observed within the various core divisions. The alkaline suite in the sequence above the upper hydrothermal unit (upper shaded area) is identified by enrichment in Zr relative to the tholeiites. The Zr/Y diagram demonstrates that the Hole 801C basalts are normal MORB comparable in chemistry to modern East Pacific Rise (EPR) tholeiites (Leg 185). MAR = Mid-Atlantic Ridge.

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