HF, ND, SR, PB ISOTOPE SYSTEMATICS OF REJUVENATED LAVAS FROM THE NORTH ARCH VOLCANIC FIELD

The North Arch Volcanic field falls along a transect defined by the Kaula, Niihau, Kauai islands that cuts across the Hawaiian plume chain. The alkali lavas erupting along this transect allow us to investigate the spatial heterogeneity of the rejuvenated component in the Hawaiian mantle plume. The North Arch lavas have relatively radiogenic ¹⁴³Nd/¹⁴⁴Nd, ranging from 0.513070 to 0.513102, and relatively unradiogenic ⁸⁷Sr/⁸⁶Sr, ranging from 0.70301 to 0.70317. The analyzed lavas extend to lower ²⁰⁸Pb/²⁰⁴Pb ratios than previously reported for the North Arch, ranging from 37.70 to 37.83, and the ¹⁷⁶Hf/¹⁷⁷Hf varies from 0.283147 to 0.283188. In εHf versus εNd isotope space the North Arch lavas define a steep array with a slope of 3 that is steeper than the mantle array and the Hawaiian shield stage lavas. The steep North Arch array is similar to other rejuvenated magma sources defined by the pyroxenite xenoliths in Kaula and Salt Lake Crater, Oahu, but it is offset to more radiogenic Nd than those. The radiogenic Hf and Nd isotopes and steep Hf-Nd arrays defined by the other rejuvenated magma sources is consistent with a depleted component with relatively radiogenic Hf for a given Nd, that is different than Pacific MORB. The Nd isotopes of magmas at the edges of the Kaula-North Arch transect extend to more radiogenic ratios than in the center, implying greater contribution of a depleted component at the periphery of the plume than along the plume track. Yet, the non-overlapping arrays in Hf-Nd space of the North Arch and Kaula pyroxenites also suggest that this depleted component may also be heterogeneous within the Hawaiian plume.