Origin of depleted components in basalt related to the Hawaiian hot spot: Evidence from isotopic and incompatible element ratios

Abstract

The radiogenic isotopic ratios of Sr, Nd, Hf, and Pb in basaltic lavas associated with major hot spots, such as Hawaii, document the geochemical heterogeneity of their mantle source. What processes created such heterogeneity? For Hawaiian lavas there has been extensive discussion of geochemically enriched source components, but relatively little attention has been given to the origin of depleted source components, that is, components with the lowest 87Sr/86Sr and highest 143Nd/144Nd and 176Hf/177Hf. The surprisingly important role of a depleted component in the source of the incompatible element‐enriched, rejuvenated‐stage Hawaiian lavas is well known. A depleted component also contributed significantly to the ∼76–81 Ma lavas erupted at Detroit Seamount in the Emperor Seamount Chain. In both cases, major involvement of MORB‐related depleted asthenosphere or lithosphere has been proposed. Detroit Seamount and rejuvenated‐stage lavas, however, have important isotopic differences from most Pacific MORB. Specifically, they define trends to relatively unradiogenic Pb isotope ratios, and most Emperor Seamount lavas define a steep trend of 176Hf/177Hf versus 143Nd/144Nd. In addition, lavas from Detroit Seamount and recent rejuvenated‐stage lavas have relatively high Ba/Th, a characteristic of lavas associated with the Hawaiian hot spot. It is possible that a depleted component, intrinsic to the hot spot, has contributed to these young and old lavas related to the Hawaiian hot spot. The persistence of such a component over 80 Myr is consistent with a long‐lived source, i.e., a plume.