The Réunion Island mantle plume – isotopic constraints on core addition or ancient silicate component?

The geochemical composition of ocean island basalts (OIB) from Réunion Island has been controversially interpreted as recording either interaction between the mantle and Earth’s core [1] or the preservation of an ancient, Hadean silicate reservoir isolated since early Earth differentiation [2,3]. Resolving this debate bears directly on the nature of deep mantle heterogeneity, the longevity of early-formed reservoirs, and the efficiency of whole-mantle mixing through time. In particular, the extinct ¹⁸²Hf-¹⁸²W decay system provides a powerful tracer of both, core contribution due to the strong siderophile behaviour of W during core formation as well as early silicate differentiation processes because of the short half-life of ¹⁸²Hf.

Here we present new high-precision radiogenic W isotope data (μ¹⁸²W) for 39 basaltic lavas from Réunion Island, complemented by major and trace element compositions and long-lived radiogenic isotope ratios including ¹⁴³Nd/¹⁴⁴Nd, ⁸⁷Sr/⁸⁶Sr, and ^206,207,208Pb/²⁰⁴Pb. Measured μ¹⁸²W values range from 0 to –11, fully overlapping with the range reported in previous studies of Réunion and related plume products [1–3]. These results confirm that the Réunion mantle source is isotopically heterogeneous and requires the involvement of a geochemically distinct component not represented in depleted upper mantle reservoirs.

By integrating short-lived and long-lived isotope systematics with trace element constraints, we evaluate the origin of this component and its implications for deep Earth processes. In particular, we assess whether the observed μ¹⁸²W anomalies are more consistent with contributions from an early-formed silicate reservoir that avoided complete mantle homogenization, or with addition of core-derived material to the mantle plume source. Our dataset is discussed in the context of isotopic findings that provide compelling evidence for ongoing or episodic core–mantle chemical exchange recorded in OIB sources [4].

The combined data of Réunion basalts indicate that core addition is the most likely process to explain the chemical and isotopic observations. Our findings allow qualitative constraints on the mass exchange between the Earth’s core and mantel and highlight the importance of integrating multiple isotope systems to disentangle the complex history of mantle plume sources and their role in recording the mass exchange from core to surface on Earth.

References:

[1] Rizo et al. (2019) Geochemical Perspectives Letters, 6–11.

[2] Peters et al. (2018) Nature, 555, 89–93.

[3] Pakulla et al. (2025) Earth and Planetary Science Letters, 653.

[4] Messling et al. (2025) Nature, 642, 376–380.