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USGS CMG InfoBank: Regional Metamorphism

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Comment: 14:52 - 15:42 (00:50)
Source: Annenberg/CPB Resources - Earth Revealed - 18. Metamorphic Rocks
Keywords: "James Sadd", "regional metamorphism", amphibolite, layering, quartzite, "mica schist", "aluminum silicate", sillimanite, "sedimentary bed", biotite, "directed stress", shear

Our transcription: This is a good example of a well-layered rock produced by regional metamorphism in a so-called amphibolite facies.
It contains of alternating layers, the light, of quartzite, and of dark, a mica schist bearing the aluminum silicate mineral sillimanite.
At first thing you would think these are relic sedimentary beds, but they are not; they've been structurally transposed from sedimentary beds into tectonically bounded layers.
Here you can see two of the biotite-rich layers coming together to constitute a single layer, so there has been a great deal of directed shearer pressure through this rock that is produced as well-layered aspect to it.

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