Editing Allochthon (section)

{{Short description|Large block of rock which has been moved from its original site of formation}}
{{for|the Dutch demographical term|Allochtoon}}
[[image:thrust system en.jpg|thumb|right|upright=1.6|Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a [[nappe]]. If an [[erosion]]al hole is created in the nappe that is called a [[window (geology)|window]]. A [[klippe]] is a solitary outcrop of the nappe in the middle of autochthonous material.]]

An '''allochthon''', or an allochthonous block, is a large block of rock which has been moved from its original site of formation, usually by [[thrust fault|low angle thrust faulting]].<ref>{{cite book|last1=DiPietro|first1=Joseph A.|title=Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History|date=December 21, 2012|publisher=Newnes|isbn=9780123978066|page=343|url=https://books.google.com/books?id=vZWWAA-USoUC&pg=PA343|access-date=10 February 2016}}</ref> The term is derived from Greek: ''allo'', meaning other, and ''chthon'', meaning earth. For other possible mechanisms see [[obduction]]. 

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 (geology)|autochthon]] beneath the allochthon, the hole is called a "[[window (geology)|window]]" (or fenster). In generalized terms, the term is applied to any geologic units that originated at a distance from their present location.<ref>Allaby, Michael. A Dictionary of Geology and Earth Sciences (Oxford Quick Reference) (p. 353). OUP Oxford. Kindle Edition.</ref>

In the United States there are three notable allochthons, all of which were displaced nearly 50 km (31 miles) along thrust faults. The [[Golconda_Thrust|Golconda]] and Robert Mountains allochthons are both found in [[Nevada]], a product of the Antler orogeny in the late Devonian period. Another is the Taconic allochthons found in [[New York (state)|New York]], [[Massachusetts]] and [[Vermont]] formed from the collision of the Taconic magmatic arc with the super-continent [[Laurentia]] in the late Cambrian period.<ref>{{cite book|last1=DiPietro|first1=Joseph A.|title=Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History|date=December 21, 2012|publisher=Newnes|isbn=9780123978066|page=416|url=https://books.google.com/books?id=vZWWAA-USoUC&pg=PA416|access-date=18 April 2021}}</ref>