North_america_basement_rocks.png


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Description

North American cratons and basement rocks.

As radiometric ages were determined for the shield-like rocks on the continents which were either exposed at the surface, underlay the flat rocks, or were within the interior of the mountain belts, patterns of age intervals were determined. These old rocks have been called the "basement". This has been interpreted to mean that the continents had somehow grown by development of rock assemblages with these characteristic age parameters. The expanding continental nuclei are part of the "craton" which consist of both exposed and buried basement rocks.
Date
Source http://rst.gsfc.nasa.gov/Sect2/14strprv.jpg or http://instruct.uwo.ca/earth-sci/300b-001/14strprv.gif English Wikipedia, original upload 22 April 2005 by Berkut Originally uploaded by User:SEWilco as Image:North america basement rocks.jpg. Replaced when this better version found.
Author USGS
Permission
( Reusing this file )
Public domain
This image is in the public domain in the United States because it only contains materials that originally came from the United States Geological Survey , an agency of the United States Department of the Interior . For more information, see the official USGS copyright policy .

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derivative works

Derivative works of this file: North america and scandinavia basement rocks.png

Captions

North American cratons and basement rocks

Items portrayed in this file

depicts

5 March 2015