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Can a Continent Sink?

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Adam Hawthorne
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« on: April 08, 2007, 11:31:11 pm »

Orogeny
 
Orogeny (Greek for "mountain generating") is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within a time frame.


Orogenic events occur solely as a result of the processes of plate tectonics; the problems which were investigated and resolved by the study of orogenesis contributed greatly to the theory of plate tectonics, coupled with study of flora and fauna, geography and mid ocean ridges in the 1950s and 1960s.

The physical manifestations of orogenesis, the process of orogeny, are orogenic belts or orogens. An orogen is different from a mountain range in that an orogen may be completely eroded away, and only recognizable by studying (old) rocks that bear the traces of the orogeny. Orogens are usually long, thin, arcuate tracts of rocks which have a pronounced linear structure resulting in terranes or blocks of deformed rocks, separated generally by dipping thrust faults. These thrust faults carry relatively thin plates (which are called nappes, and differ from tectonic plates) of rock in from the margins of the compressing orogen to the core, and are intimately associated with folds and the development of metamorphism.

The topographic height of orogenic mountains is related to the principle of isostasy, where the gravitational force of the upthrust mountain range of light, continental crust material is balanced against its buoyancy relative to the dense mantle.

Erosion inevitably takes its course, removing much of the mountains, leaving the core or mountain roots, which may be exhumed by further isostatic events balancing out the loss of elevated mass. This is the final form of the majority of old orogenic belts, being a long arcuate strip of crystalline metamorphic rocks sequentially below younger sediments which are thrust atop them and dip away from the orogenic core.

http://en.wikipedia.org/wiki/Orogeny
« Last Edit: April 08, 2007, 11:34:08 pm by Adam » Report Spam   Logged


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