Allochthon

An allochthon, or an allochthonous block, is a large block of rock which has been moved from its original site of formation, usually by low angle thrust faulting.[1] An allochthon which is isolated from the rock that pushed it into position is called a klippe. If an allochthon has a "hole" in it so that one can view the autochthon beneath the allochthon, the hole is called a "window" (or Fenster). Etymology: Greek; 'allo' = other, and 'chthon' = earth. In generalized terms, the term is applied to any geologic units that originated at a distance from their present location [2] For comparison, see also Autochthon.

Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window. A klippe is a solitary outcrop of the nappe in the middle of autochthonous material.

In the United States there are three notable allochthons; all of which were displaced nearly 50 km (31 miles) along thrust faults. The Golconda and Robert Mountains allochthons are both found in Nevada, a product of the Antler Orogeny in the Late-Devonian period. The third is the Taconic allochthons found in New York, Massachusetts and Vermont formed from the collision of the Taconic magmatic arc with the super-continent Laurentia in the Late-Cambrian period. [3]

See also

References

  1. DiPietro, Joseph A. (December 21, 2012). Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Newnes. p. 343. ISBN 9780123978066. Retrieved 10 February 2016.
  2. Allaby, Michael. A Dictionary of Geology and Earth Sciences (Oxford Quick Reference) (p. 353). OUP Oxford. Kindle Edition.
  3. DiPietro, Joseph A. (December 21, 2012). Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Newnes. p. 416. ISBN 9780123978066. Retrieved 18 April 2021.
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