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upright=1.6, 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 (geology)">window
A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent ma ...
. 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
low angle thrust faulting. 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 beneath the allochthon, the hole is called a "
window
A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent ma ...
" (or fenster). In generalized terms, the term is applied to any geologic units that originated at a distance from their present location.
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
Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
, a product of the Antler orogeny in the late Devonian period. Another is the Taconic allochthons found in
New York,
Massachusetts
Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...
and
Vermont
Vermont () is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, New Hampshire to the east, New York (state), New York to the west, and the Provinces and territories of Ca ...
formed from the collision of the Taconic magmatic arc with the super-continent
Laurentia in the late Cambrian period.
See also
*
Accretion (geology)
*
Continental collision
In geology, continental collision is a phenomenon of plate tectonics that occurs at Convergent boundary, convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroy ...
*
Orogeny
Orogeny () is a mountain-mountain formation, building process that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is tectonic uplift, u ...
References
Structural geology
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