Editing Metamorphism (section)

{{Short description|Change of minerals in pre-existing rocks without melting into liquid magma}}
{{Other uses}}
[[Image:Metamorphic reaction EN.svg|thumb|upright=1.35|Schematic representation of a [[metamorphic reaction]]. Abbreviations of minerals: act = [[actinolite]]; chl = [[Chlorite group|chlorite]]; ep = [[epidote]]; gt = [[garnet]]; hbl = [[hornblende]]; plag = [[plagioclase]]. Two minerals represented in the figure do not participate in the reaction, they can be [[quartz]] and [[K-feldspar]]. This reaction takes place in nature when a [[mafic rock]] goes from [[amphibolite facies]] to [[greenschist facies]].]]

[[File:Thin section of garnet-mica-schist.jpg|thumb|upright=1.35| A [[Polarized light microscopy|cross-polarized]] [[thin section]] image of a [[garnet]]-[[mica]]-[[schist]] from [[Salangen Municipality]], Norway showing the strong strain fabric of schists. The black crystal is garnet, the pink-orange-yellow  colored strands are [[muscovite]] mica, and the brown crystals are [[biotite]] mica. The grey and white crystals are [[quartz]] and (limited) [[feldspar]].]]

'''Metamorphism''' is the transformation of existing [[Rock (geology)|rock]] (the [[protolith]]) to rock with a different [[mineral]] composition or [[Texture (geology)|texture]]. Metamorphism takes place at temperatures in excess of {{cvt|150|C||sigfig=1}}, and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation.{{sfn|Marshak|2009|p=177}} Metamorphism is distinct from [[weathering]] or [[diagenesis]], which are changes that take place at or just beneath Earth's surface.{{sfn|Vernon|2008|p=1}}

Various forms of metamorphism exist, including [[Regional metamorphism|regional]], [[Contact metamorphism|contact]], [[Hydrothermal metamorphism|hydrothermal]], [[Shock metamorphism|shock]], and [[Dynamic metamorphism|dynamic]] metamorphism. These differ in the characteristic temperatures, pressures, and rate at which they take place and in the extent to which reactive fluids are involved. Metamorphism occurring at increasing pressure and temperature conditions is known as ''prograde metamorphism'', while decreasing temperature and pressure characterize ''retrograde metamorphism''.

[[Metamorphic petrology]] is the study of metamorphism. Metamorphic petrologists rely heavily on [[statistical mechanics]] and [[experimental petrology]] to understand metamorphic processes.