World Library  
Flag as Inappropriate
Email this Article

Tectonic phase

Article Id: WHEBN0019906478
Reproduction Date:

Title: Tectonic phase  
Author: World Heritage Encyclopedia
Language: English
Subject:
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Tectonic phase

A tectonic phase or deformation phase is in structural geology and petrology a phase in which tectonic movement or metamorphism took place. Tectonic phases can be extensional or compressional in nature.

When numerous subsequent compressional tectonic phases share the same geodynamic cause (usually some plate tectonic mechanism) this is called an orogeny. During an orogeny tectonic phases lead to mountain building, which causes deformation and metamorphism of rocks. In most Phanerozoic orogenies many tectonic phases are distinguished.

Tectonic phases in basin geology and sedimentary rocks

According to Steno's principle of original horizontality, sedimentary rocks are normally deposited as horizontal layers. When tectonic movement occurs sedimentary layers can be tilted. under such circumstances, the sedimentary planes will have a dip (an angle with a horizontal reference plane). When new sedimentary layers are deposited on top of tilted ones, they will have an angle with the older ones, a structure which is called an angular unconformity. Any angular unconformity is prove that a tectonic phase took place between the deposition of the layers below and on top of it.

It is important to know if the tectonic phase was a longer event or if it was local or regional. Tectonic phases can be important events that affected large areas. The Alleghenian orogeny in North America (during the Carboniferous period) for example can be found as an angular unconformity between rock layers in large parts of that continent.

When a tectonic phase occurred while sedimentation of new sediments continued, every new layer will have a slightly different dip from the one below. The result is a sequence of sediments that wedges out in one direction. This is usually the case on the margins of geologic basins.

Tectonic phases in metamorphic rocks

In petrology, metamorphic phases can be distinguished by analysis of minerals and microstructures (petrography) in metamorphic rocks. By analysing the sequence in which the minerals and structures were formed, more than one phase can be found in most metamorphic rocks (this is called polymetamorphism). By radiometric dating the absolute age of the different phases of mineral growth can be determined, showing when the rock was under certain pressure-temperature conditions. The obtained age is not necessarily the age of a tectonic phase, but can show when the tectonic phase ended and crystallisation of new minerals occurred.

See also

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.