ISOTOPE SOURCES OF ALKALINE MAGMATISM IN THE CLARION FRACTURE-ZONE, PACIFIC-OCEAN

The Pb-Sr-Nd isotope compositions of alkaline basalts from the Clarion Fracture Zone provide evidence for the lateral heterogeneity of the u nderlying mantle. The contributions of a variety of mantle reservoirs (DM, EM1, and HiMu) were estimated using alkaline basalts from discret e portions of the fracture zone. The mantle source of basalts in its e astern sector was formed by the interaction of depleted mantle materia l and a mantle plume. The isotope signatures of basalts from the centr al sector indicate that the depleted mantle source (like DM) was mixed with approximately 0.15-1% pelagic sediments. The mantle Pb-Sr-Nd sig natures of basalts from the western sector differ from the respective signatures of lavas from the nearby Hawaiian Islands, but an similar t o those of oceanic-island lavas from the South Pacific.