Early mantle processes inferred from high-precision 182W-142Nd isotope systematics of igneous rocks from the Singhbhum Craton, India

The scarcity of well-preserved exposed Precambrian rocks as well as post-emplacement metamorphism and alteration hamper a detailed understanding of mantle differentiation processes on the early Earth. This issue can be overcome by powerful tools such as the short-lived isotope decay series such as ¹⁸²Hf-¹⁸²W and ¹⁴⁶Sm-¹⁴²Nd isotope systems that only record radiogenic ingrowth during the Hadean Eon.

This study focuses on high-precision measurements of ¹⁸²W/¹⁸⁴W and¹⁴²Nd/¹⁴⁴Nd isotope compositions using MC-ICP-MS ([1], [2]) of ultramafic, mafic and felsic rocks from the Singhbhum Craton (India) that range in their crystallization age from 3.5 to 1.6 Ga. Due to the susceptibility of W to secondary fluid-rock interactions, the rock samples that were chosen were initially tested for mobility of W by a comparison of W with other equally incompatible elements such as Th, Ta, U [3] that were obtained by ICP-MS with a focus on precise measurements of High Field Strength Element concentrations (<6% uncertainty). Preliminary ¹⁸²W isotope data that ranges from µ¹⁸²W= -1.6 to -0.7 (±2-3 ppm; 95% CI) shows a slight tendency to negative values that are unresolvable from the modern mantle value. This data, in combination with robust ¹⁴²Nd isotope constraints can give fresh insights into early mantle differentiation of the Singhbhum Craton and access the timescales of homogenization of the ambient mantle with late accreted material.

[1] Tusch et al. (2022), PNAS 119

[2] Hasenstab-Dübeler et al. (2022), Chem. Geo. 614

[3] König et al. (2011), Geochim. Cosmochim. Acta 75