Morton Gneiss

The Morton Gneiss is an Archean-age migmatitic gneiss found in the Minnesota River Valley of southwestern Minnesota. Zircon crystals from the gneiss have been dated to 3524 ± 9 Ma. Zircons from the Montevideo Gneiss from Chippewa County have an age of 3485 ± 10 Ma.[1]

Its type locality is in Morton, Minnesota where it is also known as "Rainbow Gneiss", and is quarried as a facing stone for buildings.[2]

The Morton Gneiss is the oldest rock unit in the United States.[3]

References

  1. ↑ M.E. Bickford, J.L. Wooden and R.L. Bauer, 2006 SHRIMP study of zircons from Early Archean rocks in the Minnesota River Valley: Implications for the tectonic history of the Superior Province, GSA Bulletin, v. 118 no. 1-2 p. 94-108
  2. ↑ Minnesota Geological Survey
  3. ↑ Emporia State University
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