Geochemistry, petrography and least-squares fractionation at DSDP Leg 64 Holes

Major-element, trace-element, and mineralogic data from basalts drilled during Leg 64 indicate that a wide spectrum of N-type MORB have been erupted in the Gulf of California. Leg 64 basalts have chemical and mineralogical characteristics broadly similar to those from the East Pacific Rise and Nazca Plate. They are not nearly so evolved as basaltic lavas recovered from the Galapagos Spreading Center. Trace-element data suggest that several N-type mantle sources or a spatially heterogeneous mantle were partially melted to generate the spectrum of basalts recovered during Leg 64. However, simple, closed-system crystal fractionation does not adequately explain all of the observed chemical and mineralogical features. Mixing of primitive magmas, with observed An-rich Plagioclase xenocrysts and fractionating magmatic liquids, is a plausible mechanism which can help to explain the evolution of basaltic magmas in the Gulf of California.