Archean to Proterozoic siliciclastic rocks display bulk silicate Earth-like µ182W and µ142Nd compositions

Short-lived isotope systems such as ¹⁸²Hf-¹⁸²W (t_1/2 = 8.9Ma) and ¹⁴⁶Sm-¹⁴²Nd (t_1/2 ≈ 100 Ma) are pivotal tools in understanding Hadean and early Archean geodynamic processes, including core formation, silicate differentiation, and crust formation. However, there is no consensus on the average crustal composition of ¹⁸²W and ¹⁴²Nd, because excesses, deficits, and bulk silicate Earth (BSE)-like µ¹⁸²W and µ¹⁴²Nd values have been interpreted as regional rather than global average crustal compositions [1, 2].

To resolve this discrepancy, we analysed the µ¹⁸²W and µ¹⁴²Nd composition of Archean to Proterozoic (3.2 Ga to 1.2 Ga) siliciclastic rocks from the Kaapvaal Craton (South Africa) and the Yangtze Block (South China). These sedimentary rocks, integrating isotope signals from broad source regions, best represent the average upper continental crust composition. Trace element ratios (e.g., W/Th, La/Yb, Th/Sc) and long-lived radiogenic isotope compositions (¹⁴³Nd/¹⁴⁴Nd, ¹⁷⁶Hf/¹⁷⁷Hf) infer a mixture of dominantly felsic, but also mafic juvenile igneous source rocks. Except for one shale with ¹⁸²W deficits, all samples exhibit BSE-like µ¹⁸²W and µ¹⁴²Nd values. Consequently, our µ¹⁸²W and µ¹⁴²Nd data set represents the best current estimate for the composition of the upper continental crust between 3.2 and 1.2 Ga. The absence of resolvable µ¹⁸²W and µ¹⁴²Nd anomalies also constrains the corresponding mantle source compositions. This suggests that anomalous µ¹⁸²W and µ¹⁴²Nd compositions [1,3] likely originated from locally restricted and isolated mantle sources.

[1] Mundl et al. 2018; Chem.Geol.

[2] Boyet et al. 2021; GCA

[3] Willbold et al. 2011; Nature