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

Trisrota Chaudhuri,Mingzhu Ma,Dunyi Liu,Yusheng Wan,Rajat Mazumder

doi:10.1038/s41598-018-25494-6

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; ɛHf[t] = −2.5 to −5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated ɛHf[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.

Highlights

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
The Paleoarchean (~3.4 Ga) Tonalite-Trondhjemite-Granodiorite gneisses (TTG), called the Older Metamorphic Tonalitic Gneiss (OMTG), of the Paleo-Mesoarchean Singhbhum Craton of Eastern India and confirm that the OMTG holds the hitherto oldest precursor rock recorded in India
According to Hofmann and Mazumder[28], the OMTG represents a suite of TTGs that formed over an extended period between 3.53-3.45 Ga, whereas the Older Metamorphic Group (OMG) represents a supracrustal assemblage that formed as a greenstone succession

Summary

Introduction

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. The Paleoarchean (~3.4 Ga) Tonalite-Trondhjemite-Granodiorite gneisses (TTG), called the Older Metamorphic Tonalitic Gneiss (OMTG), of the Paleo-Mesoarchean Singhbhum Craton of Eastern India and confirm that the OMTG holds the hitherto oldest precursor rock recorded in India. The oldest age obtained from the OMTG is a whole-rock Sm-Nd isochron age of 3775 ± 89 Ma34 This age was later questioned and subsequently amended by Moorbath et al.[35] to be closer to 3.4 Ga. other older ages recently reported from the OMTG include an age of 3664 ± 79 Ma, which was derived from a whole-rock Pb-Pb isochron[36], and a xenocrystic zircon core age of ~3.61 Ga (207Pb/206Pb in situ LA-ICP MS dating), which was found within a ~3.4 Ga zircon[37]. The ∼3.6 Ga xenocrysts from the OMTG37 and OMG quartzites[30] indicate that felsic crustal formation was initiated in the Singhbhum Craton well before the major phase of emplacement of the OMTG

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Conclusion