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USGS CMG InfoBank: Deformation of Rocks

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Comment: 13:14 - 14:50 (01:36)
Source: Annenberg/CPB Resources - Earth Revealed - 6. Plate Dynamics
Keywords: "Scott Paterson", deformation, strain, rock, "distortion rate", fracture, stress, fold, flow, mantle, temperature, "geologic time", "plate tectonics"

Our transcription: We can use silly putty as an analogy for rocks, particularly if we're interested to see the effects of the rate of distorting or straining the rock.
I can give you several examples.
I've got three different piles here of the exact same material.
In one case I can take the silly putty, and if I apply a very fast rate of deformation to it, we can just make it fracture.
This might be a good analogy for what would happen near the surface of the Earth where our rocks are cold, and if we deform them quickly, they would fracture like that.
We could take the same material, and I could again apply stress to it, but if I do it at a much slower rate, essentially I have a slower strain rate, then we can see that my material will flow instead of fracture.
This might be a good analogy to what would happen at depth where the rocks are hotter and we're deforming at very slow long term rates, and we could get folds and things like that.
We can even go to a more extreme case, and we'll again take the same material, and I can just place it on my block right here, and we'll essentially let gravity be the only stress operating on that silly putty.
In this case, we'll see with time that the rock will still flow although at a much slower rate than we saw in the previous example.
In the same way mantle rocks can deform plastically because of their high temperature when stressed over very long time periods.

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