Evolution of tungsten isotope systematics in the Mauna Kea volcano provides new constraints on anomalous µ182W and high 3He/4He in the mantle

Highly siderophile element abundances and ¹⁸²W/¹⁸⁴W and ¹⁸⁷Os/¹⁸⁸Os were determined for a suite of Mauna Kea lavas from the Hawaiian Scientific Drilling Project phase 2 drill core. The new analyses, combined with previous measurements, compose the largest database for µ¹⁸²W (the parts-per-million deviation of ¹⁸²W/¹⁸⁴W from a terrestrial standard) for a single volcano (n = 16). Although most lavas analyzed are characterized by negative µ¹⁸²W values, lavas with values similar to the modern bulk silicate Earth are found throughout the entire stratigraphic column. This suggests that components with normal µ¹⁸²W are collocated with components that host µ¹⁸²W deficits in the plume. Negative µ¹⁸²W values are associated with elevated ³He/⁴He, as well as elevated Ti and Nb. These correlations may link µ¹⁸²W anomalies to ancient deep mantle crystal-liquid fractionation processes. Consistent with previously measured ³He/⁴He (R/R_A) in the drill core, the magnitude of negative µ¹⁸²W values was greatest when Mauna Kea was close to the plume axis then generally decreased over the ∼400 kyr captured by the stratigraphic section. The component with anomalous µ¹⁸²W was either concentrated near the plume axis, or was more effectively sampled by melting near the plume axis where the temperature excess was greatest, suggesting it was less fusible than the dominant plume components. The process leading to the generation of a mantle component with a negative µ¹⁸²W anomaly could either be related to some form of core-mantle isotopic equilibration, or early-Earth fractionation within the silicate Earth. At present each possibility remains viable.