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

ABSTRACT: Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb analyses of zircons from Paleoarchean (~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 176Hf/177Hfinitial compositions (0.27995?±?0.0009 to 0.28001?±?0.0007; ?Hf[t]?=?-2.5 to -5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated ?Hf[t] compositional array of the Hadean xenocrysts indicates a mafic protolith with 176Lu/177Hf ratio of ?0.019 that was reworked during ?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 ?3.67 Ga (average 176Hf/177Hfinitial 0.28024?±?0.00007) and ~3.4 Ga zircons (average 176Hf/177Hfinitial?=?0.28053?±?0.00003) from the same OMTG samples and two other Paleoarchean TTGs dated at ~3.4 Ga and ~3.3 Ga (average 176Hf/177Hfinitial 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.

SUBMITTER: Chaudhuri T 

PROVIDER: S-EPMC5935743 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature