The spatio-temporal evolution of 182W and 142Nd in the Deccan-La Réunion plume

• New µ 182 W and µ 142 Nd data for La Réunion and Deccan LIP. • No µ 142 Nd anomalies were detected in basalts from Deccan and La Réunion. • No correlation between µ 182 W and µ 142 Nd for La Réunion lavas. • Deccan basalts differ in µ 182 W from La Réunion basalts. • A likely origin of 182 W deficits from ancient silicate reservoirs. Variations of the short-lived decay products 182 W and 142 Nd that formed approximately during the first 60 and 500 million years after solar system formation are pivotal in our understanding of Hadean processes and homogenization of Earth's mantle. For example, a coupling of 142 Nd and 182 W anomalies for the Deccan-La Réunion plume has been previously suggested to mirror a combined involvement of core-mantle interaction and Hadean silicate material, possibly stored in Large Low Shear Wave Velocity Provinces (LLSVPs). However, the limited availability of such short-lived isotope data for basalts from the Deccan Volcanic Province (DVP) made it difficult to assess this model closely. In this study, we provide new combined µ 142 Nd and µ 182 W data for ten selected samples of the DVP and one TTG from the Dharwar Craton basement, now covering different mantle endmembers of the DVP. Additionally, we provide new µ 142 Nd data for six volcanic rocks from La Réunion that were previously analyzed for 182 W. We do not find evidence for a correlation between µ 142 Nd and µ 182 W in contrast to previous suggestions. Our data show that the involvement of mantle lithosphere and crustal components influences the µ 182 W compositions of the DVP samples. Values of µ 182 W (-4.2 ± 3.0) of such contaminated DVP samples overlap with the compositional field of volcanic rocks from La Réunion (-4.9 ± 1.5). The asthenospheric endmember of the DVP displays resolvable larger µ 182 W deficits as low as -12.0 ± 2.3. Additionally, the asthenospheric DVP endmember also displays more unradiogenic 206 Pb/ 204 Pb ratios and low Δ 207 Pb/ 206 Pb compared to La Réunion lavas and DVP lavas that assimilated lithospheric material. With regards to the two endmember models previously proposed for W isotope anomalies in mantle plumes, neither core-derived W nor an ancient silicate component with anomalous 182 W can be completely ruled out at this stage. However, due to the covariation of Pb and W isotopes and lower W/Th ratios in asthenosphere-derived DVP lavas, we currently favour a recycled mafic restite component of Hadean age as a source for the 182 W deficits in the Deccan-La Réunion plume.