Recent GLORIA surveys and dredging have discovered a large field of young alkalic flood basalts across the flexural arch north of the Hawaiian island chain. These rocks represent a significant and previously unknown part of Hawaiian volcanic history, and promise to advance greatly our understanding of hot-spot volcanism. Drs. Mahoney and Sinton will oversee isotopic and trace element analyses on 20-30 dredge samples from this region in order to determine mantle sources and gain insight into the magmatic history of this largery of this large flow field. Previous understanding of hotspot, mid-plate volcanic (like those of the Hawaiian islands) have identified three phases: 1) the major shield building episode of tholeitic composition; 2) a minor (<1% by volume) alkalic cap; and 3) a small outpouring of silica-poor, " rejuvenated" lavas after a few million years of quiesence. Initial studies by Clague (USGS, a not-cost collaborator on this request) show the arch volcanics are closest in character to this last, "rejuvenated" suite of MORB-like rocks. Mahoney and Sinton hope to gain better understanding of the nature and variability of probable mantle sources, and the respective roles of partial melting, magma mixing and fractional crystallization.
