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USGS CMG InfoBank: Vermont Garnets

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Comment: 23:33 - 25:07 (01:34)
Source: Annenberg/CPB Resources - Earth Revealed - 18. Metamorphic Rocks
Keywords: "John Rosenfeld", Vermont, garnet, "geologic time", continent, Eurasia, Africa, America, supercontinent, Pangea, "convergent plate", "Appalachian Mountains", "North American Continent", fold, nappe, burial, crystal, "snowball garnet", "geologic time", "plate tectonics"

Our transcription: The Vermont garnets began growing about 380 million years ago as the continents of Eurasia and Africa drifted toward the Americas to form the supercontinent of Pangea.
The convergence of the plates gradually heaved up the rocks of Northeastern North America to create the Appalachian Mountain range pushing the rocks into huge flat lying folds called "nappes."
Buried deep inside these giant folds of rock tiny garnet crystals echo the twisting and contorting going on around them, rotating and spiraling between 20 and 30 degrees every million years.
The beauty about the garnets in Vermont is that these are, the ones we measured were snowball garnets, and so we get some other useful information from the garnets studied in Vermont.
That information tells us how fast the rocks were deforming, and in other words, how fast the garnets were rotating.
That tells us how fast the rocks in the surroundings around the garnets were causing that rotation were deforming, and that is something that has never been measured before.
That's a considerable interest for people studying tectonism because we're actually measuring the rates at which the rocks get folded.
And that's another factor we're interested in.

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