Geochemical Characteristics of Mantle Sources of North Arch Alkalic Volcanism, Hawaii

The North Arch volcanic field is located on the seafloor between 100 and 390 km north of Oahu, and has an estimated total volume between 1000 and 1250 km³ (Clague et al., 1990, 2000, 2001). The alkalic volcanism is located far from the axis of Hawaiian volcanism and is characterized by eruption of primitive, low-silica, alkali-rich magmas (Clague et al., 1990). We present new Pb and Sr isotope compositions and major and trace element contents of 17 North Arch alkalic lava samples collected from volcanic cones, sheet flows, and a pitcrater at water depths in excess of 4 km during two Shinkai 6500 dives. ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb isotope compositions of the samples vary from 0.70297 to 0.70313 and from 18.02 to 18.28, respectively, and show linear covariance. The samples have isotopic signatures similar to those reported for four North Arch lava samples and for Hawaiian rejuvenated stage lavas (Frey et al., 2000). Some of our new analyses extend lower in both Sr and Pb isotopes than previous North Arch analyses. The range of Sr and Pb isotope data suggest that the North Arch alkali lavas are derived from a mixed source consisting of depleted mantle and an enriched Hawaiian plume component. HFS element concentrations confirm that at least two mantle components are involved in North Arch volcanism.