When rocks undergo high temperatures and pressures that are different from how they were originally formed, they change.

Change agents for metamorphism are heat, pressure and fluids.

There two basic types of metamorphism: Regional and Contact.

Regional metamorphism takes place over large areas. When tectonic plates move, tremendous pressure is applied to the rocks over a wide area. It is the kind of pressure that builds mountains. This pressure makes profound changes in the rocks. Granite to gneiss is an example of this type of metamorphism. The layers in the metamorphosed rocks show the intense folding from the pressure applied to them.

Contact metamorphism is just what it says -- rocks are changed when they come into contact with a change agent, like heat or heated liquid. When magma intrudes into rock, the rock bakes and changes. An example of contact metamorphism is the metamorphic rock marble. Limestone subjected to intense heat becomes marble. Obviously contact metamorphism takes place over a smaller area than regional metamorphism.

Look at the links below for more detail about the way rocks undergo metamorphism.


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