Pb, Hf, Nd, and Sr Isotopic Variations of Hualalai Shield Stage Tholeiites from the Submarine North Kona Region

We present the isotope and trace element compositions of tholeiitic lavas collected from deep submarine portions of North Kona region, the west flank of Hualalai volcano. The samples were collected from the lower section of the North Kona bench (dives K218 and K219), a submarine section at Hualalai volcano's northwest rift zone (dive S690), and an elongate ridge below the central section of the bench (dive S692) during 2001 and 2002 JAMSTEC Hawaii cruises. Hualalai volcano is presently in the post-shield alkalic stage and most of its subaerial surface is covered by alkalic basalt. All analyzed samples of the pillow lavas are tholeiites that erupted during Hualalai shield stage. It is important to identify source materials involved in the volumetrically dominant stage of Hualalai volcano in order to provide constraints for the size and distribution of compositional heterogeneities of Hawaiian plume. The isotopic compositions of the submarine North Kona tholeiites are similar to the data previously reported for Mauna Loa tholeiites. The data trends define clear mixing relationships that require at least three mantle source components. The mixing is dominated by a Koolau-like enriched component and a Kea-like depleted component. The K219 data trend toward higher epsilon Hf and 87Sr/86Sr relative to the K218, S690, and S692 arrays, requiring another component similar to that observed in post-shield lavas of Hualalai volcano. Pb isotopic compositions for samples from dive K218 and K219 form distinct non-overlapping Pb-Pb arrays suggesting further source heterogeneity. Samples from dive S690 and S692 plot on both of these trends. These findings suggest small-scale compositional heterogeneity in the source regions that can be attributed to anomalous irregular 'blobs' involved in late shield stage magmatism of Mauna Loa reported in previous works.