The influence of primary magma composition, H2O and pressure on mid-ocean ridge basalt differentiation

MORB suites display variations in their chemical differentiation trends which are closely related to the incompatible element enrichment of the basalts. We examine suites of primitive to evolved basalts from the Pacific-Nazca Ridge at 28° S (mostly depleted); from the Juan Fernandez microplate region (depleted) and from the Explorer Ridge, northeast Pacific (mostly enriched). Trends for incompatible element enriched MORBs consistently show less depletion of Al2O3 and less enrichment of FeO when plotted on MgO variation diagrams.