High-pressure phase equilibria of a high-magnesia basalt and the genesis of primary oceanic basalts

High-P phase equilibria studies on a high-MgO basalt from the Tortuga ophiolite complex indicate that olivine + orthopyroxene + clinopyroxene + garnet are its liquidus phases at 25 kbar. The data are combined with results obtained on other tholeiitic basalt compositions, and are used to construct pseudoliquidus phase diagrams for evaluating and predicting the nature of primary magmas and melting of the mantle at high P.