Cretaceous-to-recent record of elevated He/He along the Hawaiian-Emperor volcanic chain

[1] Helium isotopes are a robust geochemical tracer of a primordial mantle component in hot spot volcanism. The high He/He (up to 35 RA, where RA is the atmospheric He/He ratio of 1.39 10 ) of some Hawaiian Island volcanism is perhaps the classic example. New results for picrites and basalts from the Hawaiian-Emperor seamount chain indicate that the hot spot has produced high He/He lavas for at least the last 76 million years. Picrites erupted at 76 Ma have He/He (10–14 RA), which is at the lower end of the range for the Hawaiian Islands but still above the range of modern mid-ocean ridge basalt (MORB; 6–10 RA). This was at a time when hot spot volcanism was occurring on thin lithosphere close to a spreading ridge and producing lava compositions otherwise nearly indistinguishable from MORB. After the hot spot and spreading center diverged during the Late Cretaceous, the hot spot produced lavas with significantly higher He/He (up to 24 RA). Although He/He ratios stabilized at relatively high values by 65 Ma, other chemical characteristics such as La/Yb and Sr/Sr did not reach and stabilize at HawaiianIsland-like values until 45 Ma. Our limited He/He record for the Hawaiian hot spot shows a poor correlation with plume flux estimates (calculated from bathymetry and residual gravity anomalies [Van Ark and Lin, 2004]). If He is a proxy for the quantity of primordial mantle material within the plume, then the lack of correlation between He/He and calculated plume flux suggests that variation in primordial mantle flux is not the primary factor controlling total plume flux.