Datensatz

Zusammenfassung

Ocean island basalts (OIB) show variable ¹⁸²W deficits that have been attributed to either early differentiation of the mantle or core-mantle interaction. However, ¹⁸²W variations may also reflect nucleosynthetic isotope heterogeneity inherited from Earth's building material, which would be evident from correlated ¹⁸²W and ¹⁸³W anomalies. Some datasets for OIB indeed show hints for such correlated variations, meaning that a nucleosynthetic origin of W isotope anomalies in OIB cannot be excluded. We report high-precision W isotope data for OIB from Samoa and Hawaii, which confirm previously reported ¹⁸²W deficits for these samples, but also demonstrate that none of these samples have resolvable ¹⁸³W anomalies. These data therefore rule out a nucleosynthetic origin of the ¹⁸²W deficits in OIB, which most likely reflect the entrainment of either core material or an overabundance of late-accreted materials within OIB mantle sources. If these processes occurred over Earth's history, they may have also been responsible for shifting the ¹⁸²W composition of the bulk mantle to its modern-day value. We also report Mo isotope data for some Hawaiian OIB, which reveal no resolved nucleosynthetic Mo isotopic anomalies. This is consistent with inheritance of ¹⁸²W deficits in OIB from the addition of either core or late-accreted material, but only if these materials have a non-carbonaceous (NC) meteorite-like heritage. As such, these data rule out significant contributions of carbonaceous chondrite (CC)-like materials to either Earth's core or late accretion.