When continents collide (A) or ocean crust subducts (B), rocks are altered by regional metamorphism.
Sometimes rocks are metamorphosed over large areas that are the size of many states or even several countries. This is called regional metamorphism.
How could this happen? What force has the power to squish all those rocks until the crystals change? The answer is MOVING ROCKS! Usually regional metamorphism happens as the rocky surface of the Earth moves by plate tectonics! Whenever the pieces of the Earth's surface smash into each other, metamorphic rocks form deep within the Earth.
Last modified June 20, 2003 by Lisa Gardiner.
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