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Creation of a continent recorded in zircon zoning

¹ Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
² Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
³ U.S. Geological Survey, Menlo Park, California 94305, USA
⁴ Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA
⁵ U.S. Geological Survey, Menlo Park, California 94305, USA
⁶ Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA

We have discovered a robust microcrystalline record of the early genesis of North American lithosphere preserved in the U-Pb age and oxygen isotope zoning of zircons from a lower crustal paragneiss in the Neoarchean Superior province. Detrital igneous zircon cores with ¹⁸O values of 5.1–7.1 record creation of primitive to increasingly evolved crust from 2.85 ± 0.02 Ga to 2.67 ± 0.02 Ga. Sharp chemical unconformity between cores and higher ¹⁸O (8.4–10.4) metamorphic overgrowths as old as 2.66 ± 0.01 Ga dictates a rapid sequence of arc unroofing, burial of detrital zircons in hydrosphere-altered sediment, and transport to lower crust late in upper plate assembly. The period to 2.58 ± 0.01 Ga included 80 m.y. of high-temperature (700–650 °C), nearly continuous overgrowth events reflecting stages in maturation of the subjacent mantle root. Huronian continental rifting is recorded by the youngest zircon tip growth at 2512 ± 8 Ma ( 600 °C) signaling magma intraplating and the onset of rigid plate behavior. This >150 m.y. microscopic isotope record in single crystals demonstrates the sluggish volume diffusion of U, Pb, and O in zircon throughout protracted regional metamorphism, and the consequent advances now possible in reconstructing planetary dynamics with zircon zoning.

Key Words: zircon • U-Pb • oxygen isotopes • ion probe • lower crust • Kapuskasing • Archean

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