Creation of a continent recorded in zircon zoning
- 1Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
- 2Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
- 3U.S. Geological Survey, Menlo Park, California 94305, USA
- 4Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA
- 5U.S. Geological Survey, Menlo Park, California 94305, USA
- 6Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA
Abstract
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 δ18O 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 δ18O (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.
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- Accepted 17 November 2007.
- Received 10 September 2007.
- Revision received 15 November 2007.
- The Geological Society of America, Inc.
