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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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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. However, many Archean rocks exhibit excesses of 182 W, the decay product of short-lived 182 Hf. The exact causes for these 182 W excesses, however, have remained ambiguous and it remains speculative, if the Archean 182 W anomalies and also 182 W 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 182 W isotope dataset for 3.22-3.55 Ga old rocks from the Kaapvaal Craton, Southern Africa. In expanding previous work, our study reveals widespread 182 W deficits in different rock units from the Kaapvaal Craton and also the very first discovery of a negative co-variation between short-lived 182 W and long-lived 176 Hf-143 Nd-138 Ce 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 182 Hf, i.e., the first 60 million years after solar system formation, thereby also providing lower bounds on the age of the Earth-Moon system. The striking isotopic similarity between recycled protocrust and the low 182 W endmember of modern OIBs might also be the missing link bridging 182 W 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