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Contact metamorphism does not affect as large an area
as regional metamorphism. It is associated with areas around a magma
chamber as well as other smaller igneous structures like dikes or sills.
Contact metamorphism zones can be a few centimeters to several
kilometers, especially around large plutons. The rocks that are formed
will depend on the country rock that the intrusion invades.
There are other conditions that form metamorphic
rocks. Burial metamorphism is a special type of low grade
metamorphism with low temperatures and pressures. Cataclastic metamorphism
only occurs along fault zones, usually associated with subduction or
transform zones. Conditions include high pressures under lower
temperatures.
The formation of many metamorphic rocks is still
debated. Observation of extreme pressure and temperature inside the
crust and upper mantle and how they affect rocks is difficult. Some
rocks are only slightly metamorphosed and given the term meta-igneous or
meta-sedimentary.
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