ESN 303

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Metamorphism is the process leading to changes in the mineralogy and/or

structure and/or chemical composition in a rock. These changes are due to

physical and/or chemical conditions that differ from those normally occurring

in the zone of weathering, cementation and diagenesis. They may include partial

melting as long as the bulk of the rock remains in a solid state. If change in bulk

composition is the dominant metamorphic process, the term metasomatism is

applied.

Regional metamorphism is used here as a general term for metamorphism

occurring over a wide area, as opposed to local metamorphism, and includes

orogenic, burial and ocean-floor metamorphism.