Constraints on the Source Components Involved in the Magmatism of North Arch Volcanic Field and South Arch Volcanic Field, Hawaii

Numerous Tertiary/Quaternary lava flows obscure the cretaceous sea floor at water depths in excess of 4 km along the arch crest of a broad swell surrounding the Hawaiian Islands chain. North Arch Volcanic Field (NAVF) is located downstream-side of the mantle plume and 500 - 600 km north of Kilauea which is believed to be the center of the plume. The South Arch volcanic field (SAVF) is located upstream-side of the mantle plume and 200 km south of Kilauea. These arch-type lavas are highly alkalic and compositionally similar to the rejuvenated-stage Hawaiian lavas. The arch lavas and rejuvenated-stage lavas have incompatible element-enriched characteristics, and their Sr and Nd isotopic ratios are intermediate between those of Pacific MORB and shield tholeiites. Sr and Nd isotopic signatures of NAVF, SAVF and rejuvenated stage lavas are consistent with mixing between the Hawaiian plume and the depleted component related to MORB. Comparative study of NAVF and SAVF can place constraints on possible contamination of the uppermost mantle during the dispersal of the Hawaiian mantle plume component that accompanies the moving lithospheric plate. We present the comprehensive study on Hf, Pb, Nd, and Sr isotope compositions and trace element contents for alkalic basalts collected from NAVF and SAVF. Involvement of MORB related depleted asthenosphere or lithosphere has been proposed. We examine the idea that the depleted source materials represent metasomatized old or ancient depleted oceanic lithosphere. Our results show that the South Arch and the North Arch lavas define individual steep negative trends in epsilon Hf versus 206Pb/204Pb, reflecting distinct differences between the depleted components involved in SAVF and NAVF, which suggests that the lithospheric mantle beneath Hawaii hotspot is heterogeneous.