Nature of the Earth's earliest crust from hafnium isotopes in single detrital zircons

Yuri Amelin (), Lee Der-Chuen, Alex N. Halliday and Robert T. Pidgeon
Additional contact information
Yuri Amelin: Royal Ontario Museum
Lee Der-Chuen: Department of Geological Sciences University of Michigan
Alex N. Halliday: ETH
Robert T. Pidgeon: School of Applied Geology, Curtin University of Technology

Nature, 1999, vol. 399, issue 6733, 252-255

Abstract: Abstract Continental crust forms from, and thus chemically depletes, the Earth's mantle. Evidence that the Earth's mantle was already chemically depleted by melting before the formation of today's oldest surviving crust has been presented in the form of Sm–Nd isotope studies of 3.8–4.0 billion years old rocks from Greenland1,2,3,4,5 and Canada5,6,7. But this interpretation has been questioned because of the possibility that subsequent perturbations may have re-equilibrated the neodymium-isotope compositions of these rocks8. Independent and more robust evidence for the origin of the earliest crust and depletion of the Archaean mantle can potentially be provided by hafnium-isotope compositions of zircon, a mineral whose age can be precisely determined by U–Pb dating, and which can survive metamorphisms4. But the amounts of hafnium in single zircon grains are too small for the isotopic composition to be precisely analysed by conventional methods. Here we report hafnium-isotope data, obtained using the new technique of multiple-collector plasma-source mass spectrometry9, for 37 individual grains of the oldest known terrestrial zircons (from the Narryer Gneiss Complex, Australia, with U–Pb ages of up to 4.14 Gyr (10–13). We find that none of the grains has a depleted mantle signature, but that many were derived from a source with a hafnium-isotope composition similar to that of chondritic meteorites. Furthermore, more than half of the analysed grains seem to have formed by remelting of significantly older crust, indicating that crustal preservation and subsequent reworking might have been important processes from earliest times.

Date: 1999
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DOI: 10.1038/20426

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