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Constraints on Hadean zircon protoliths from oxygen isotopes, Ti-thermometry, and rare earth elements
Department of Geological Sciences and Center for Astrobiology, University of Colorado, Boulder, Colorado 80309-0399, USA
Department of Geological Sciences and Center for Astrobiology, University of Colorado, Boulder, Colorado 80309-0399, USA
Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
We report zircon oxygen isotope ratios and reconnaissance Ti-in-zircon concentrations, guided by cathodoluminescence image studies, for detrital zircons up to 4.34 Ga from the Narryer Gneiss Complex of Western Australia. Zircon oxygen isotope results bolster the view that some Hadean (>3.85 Ga) zircon source melts were enriched in heavy oxygen, a sensitive proxy for melt contamination by sediments altered in liquid water. Zircon crystallization temperatures calculated from Ti concentration in pre-3.8 Ga zircons yield values around 680°C in all cases except for one lower value in a 4.0 Ga grain. Elevated zircon δ 18O values reported here and elsewhere, combined with low minimum-melt crystallization temperatures, and analysis of zircon/melt partitioning of rare earth elements (REEs) provide mutually consistent lines of evidence that the Hadean Earth supported an evolved rock cycle which included formation of granitic water-saturated melts, extensive continental crust, hydrosphere-lithosphere interactions, and sediment recycling within the first 150 million years of planet formation.
Received 17 August 2006; accepted 15 March 2007; published 28 June 2007.
Citation: (2007), Constraints on Hadean zircon protoliths from oxygen isotopes, Ti-thermometry, and rare earth elements, Geochem. Geophys. Geosyst., 8, Q06014, doi:10.1029/2006GC001449.
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