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USGS CMG InfoBank: Ancient Heart of North America

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Comment: 02:44 - 03:48 (01:04)
Source: Annenberg/CPB Resources - Earth Revealed - 7. Mountain Building
Keywords: "Canadian Shield", "Superior Province", craton, granulite, greenstone, "metamorphic rock", erosion, "volcanic rock", "sedimentary rock", "island arc"

Our transcription: This is the Canadian Shield, and within it is a vast region, the Superior Province, over 1,500 kilometers across.
Here the rock ranges from 2.6 billion to 4 billion years old, the ancient heart of North America.
Cratons this ancient are significant for they hold clues to the birth of continents.
The typical rocks of the Superior Province are granulite and greenstone.
"Granulite" is a high grade metamorphic rock and makes up most of the landscape.
It is too severely metamorphosed to provide much information about the past, though its exposure at the surface indicates that the crust has been deeply eroded.
Scattered throughout the granulite are intricate belts of volcanic and sedimentary rocks called "greenstones. "
Geologists interpret these as the remnants of numerous small island arcs, which have been closely packed together.

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Page Last Modified: Thu Oct 31 04:25:54 PDT 2013  (chd)