Archean crustal evolution in the Bundelkhand Craton, India: Constraints from whole rock Sr-Nd and zircon U−Pb/Hf isotopes

The formation and reworking of the continental crust is of great importance for understanding the early evolution of the Earth. Combining U−Pb/Hf isotopes in zircons with whole rock geochemical and Sr-Nd isotopic data can provide new insights on petrogenetic mechanisms, timing of magmatic events, crust-mantle interactions and magma sources for crustal material. Here we present a combined dataset of in situ zircon U−Pb and Hf as well as whole-rock Sr and Nd analyses for Archean TTGs and geochemically variable high-K granitoids from the Bundelkhand Craton, India. U−Pb zircon ages reveal that the TTGs were emplaced at 3.42 Ga, 3.33 Ga and 2.72 Ga, while the high-K granites, including sanukitoids, were emplaced between 2.57 Ga and 2.54 Ga. The high-K granitoids have higher initial ⁸⁷Sr/⁸⁶Sr isotope ratios than the TTGs. They also display a lower range in initial εNd and εHf values (from -8 to -1 and -8.9 to +0.4, respectively) compared with the TTGs (from -4 to -1.2 and -1.6 to +4.4, respectively). The Hf depleted mantle model ages calculated for high-K granitoids are 3.19−2.86 Ga and for TTGs 3.71−3.48 Ga. The U−Pb ages and chondritic to superchondritic εHf values of the TTGs provide evidence for a long-term episodic growth of juvenile crust from depleted mantle reservoirs between 3.4 and 2.7 Ga. The strongly negative εNd and εHf values of the high-K granitoids, together with geochemical features (variable compatible and incompatible elements) indicate that they were a result of multi-stage reworking of the Paleo- to Neoarchean crust and mixing with magmas extracted from an enriched mantle source during a relatively short-lived tectonic event at the end of the Archean.