Evidence of Enriched, Hadean Mantle Reservoir from 4.2-4.0 Ga zircon xenocrysts from Paleoarchean TTGs of the Singhbhum Craton, Eastern India

Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb analyses of zircons from Paleoarchean (similar to 3.4 Ga) tonalite-gneiss called the Older Metamorphic Tonalitic Gneiss (OMTG) from the Champua area of the Singhbhum Craton, India, reveal 4.24-4.03 Ga xenocrystic zircons, suggesting that the OMTG records the hitherto unknown oldest precursor of Hadean age reported in India. Hf isotopic analyses of the Hadean xenocrysts yield unradiogenic Hf-176/H-177(finitial) compositions (0.27995 +/- 0.0009 to 0.28001 +/- 0.0007; epsilon Hf[t] = -2.5 to -5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated epsilon Hf[t] compositional array of the Hadean xenocrysts indicates a mafic protolith with Lu-176/Hf-177 ratio of similar to 0.019 that was reworked during similar to 4.2-4.0 Ga. This also suggests that separation of such an enriched reservoir from chondritic mantle took place at 4.5 +/- 0.19 Ga. However, more radiogenic yet subchondritic compositions of similar to 3.67 Ga (average Hf-176/H-177(finitial) 0.28024 +/- 0.00007) and similar to 3.4 Ga zircons (average Hf-176/H-177(finitial) = 0.28053 +/- 0.00003) from the same OMTG samples and two other Paleoarchean TTGs dated at similar to 3.4 Ga and similar to 3.3 Ga (average Hf-176/H-177(finitial) is 0.28057 +/- 0.00008 and 0.28060 +/- 0.00003), respectively, corroborate that the enriched Hadean reservoir subsequently underwent mixing with mantle-derived juvenile magma during the Eo-Paleoarchean.