HIGH MAGNESIA LIQUIDS AS THE PARENTAL MAGMA FOR OCEAN-FLOOR BASALTS

The primary melt segregating from the upper mantle beneath an oceanic ridge is shown to contain ~18% MgO. Whereas these primary liquids are capable of generating the petrological features of the oceanic crust, this is not possible for tholeiitic basalts with 9-11% MgO which are highly fractionated. Compositions of liquids ranging from primary melts to high calcium picrites from the Tortuga ophiolite complex, Chile, are reported. © 1979 Nature Publishing Group.