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Long-term preservation of Hadean protocrust in Earth's mantle
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  • Jonas Tusch,
  • Elis Hoffmann,
  • Eric Hasenstab,
  • Carsten Münker,
  • Mario Fischer-Gödde,
  • Chris S. Marien
Jonas Tusch
Universität zu Köln, Universität zu Köln

Corresponding Author:[email protected]

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Elis Hoffmann
Freie Universität Berlin, Freie Universität Berlin
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Eric Hasenstab
Universität zu Köln, Universität zu Köln
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Carsten Münker
Universität zu Köln, Universität zu Köln
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Mario Fischer-Gödde
Universitiy of Cologne
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Chris S. Marien
Universität zu Köln
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Abstract

With plate tectonics operating on Earth, the preservation potential for mantle reservoirs from the Hadean Eon (>4.0 Ga) has been regarded as very small. The quest for such early remnants has been spurred by the observation that many Archean rocks exhibit excesses of 182W, the decay product of short-lived 182Hf. However, it remains speculative, if Archean 182W anomalies and also 182W deficits found in many young ocean island basalts (OIBs) mirror primordial Hadean mantle differentiation or just variable contributions from older meteorite building blocks delivered to the growing Earth. Here, we present a high-precision 182W isotope dataset for 3.22-3.55 Ga old rocks from the Kaapvaal Craton, southern Africa. In expanding previous work, our study reveals widespread 182W deficits in different rock units from the Kaapvaal Craton and also the very first discovery of a negative co-variation between short-lived 182W and long-lived 176Hf-143Nd-138Ce patterns, a trend of global significance. Amongst different models, these distinct patterns can be best explained by the presence of recycled mafic restites from Hadean protocrust in the ancient mantle beneath the Kaapvaal Craton. Further, the data provide unambiguous evidence for the operation of silicate differentiation processes on Earth during the lifetime of 182Hf, i.e., the first 60 million years after solar system formation. The striking isotopic similarity between recycled protocrust and the low 182W endmember of modern OIBs might also constitute the missing link bridging 182W isotope systematics in Archean and young mantle-derived rocks.
03 May 2022Published in Proceedings of the National Academy of Sciences volume 119 issue 18. 10.1073/pnas.2120241119