page_title: Metasomatism
hierarchical_section_title: Metasomatism
caption_attribution_description: Zones of alteration in a metagranite. This image detailes pneumatolytic or metasomatic alteration of the metagranite at Stone Mountain which manifests as sodic plagioclase, amphibole and tourmaline rich bands. Location: Stone Mountain, Georgia, U.S.A.
context_page_description: Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid.
  Synonyms to the word metasomatism are metasomatose and metasomatic process. The word metasomatose can also be used as a name for specific varieties of metasomatism.
  Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source.
  In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact metamorphic aureole adjacent to an intrusive rock mass. In the metamorphic environment, metasomatism is created by mass transfer from a volume of metamorphic rock at higher stress and temperature into a zone with lower stress and temperature, with metamorphic hydrothermal solutions acting as a solvent.
context_section_description: Metasomatism (from the Greek μετά (change) and σῶμα (body)) is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid.
  Synonyms to the word metasomatism are metasomatose  and metasomatic process. The word metasomatose can also be used as a name for specific varieties of metasomatism (for example Mg-metasomatose and Na-metasomatose).
  
  Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source.  
   In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact metamorphic aureole adjacent to an intrusive rock mass.  In the metamorphic environment, metasomatism is created by mass transfer from a volume of metamorphic rock at higher stress and temperature into a zone with lower stress and temperature, with metamorphic hydrothermal solutions acting as a solvent. This can be envisaged as the metamorphic rocks within the deep crust losing fluids and dissolved mineral components as hydrous minerals break down, with this fluid percolating up into the shallow levels of the crust to chemically change and alter these rocks.
  This mechanism implies that metasomatism is open system behaviour, which is different from classical metamorphism which is the in-situ mineralogical change of a rock without appreciable change in the chemistry of the rock. Because metamorphism usually requires water in order to facilitate metamorphic reactions, metamorphism nearly always occurs with metasomatism.
  Further, because metasomatism is a mass transfer process, it is not restricted to the rocks which are changed by addition of chemical elements and minerals or hydrous compounds. In all cases, to produce a metasomatic rock some other rock is also metasomatised, if only by dehydration reactions with minimal chemical change. This is best illustrated by gold ore deposits which are the product of focused concentration of fluids derived from many cubic kilometres of dehydrated crust into thin, often highly metasomatised and altered shear zones and lodes. The source region is often largely chemically unaffected compared to the highly hydrated, altered shear zones, but both must have undergone complementary metasomatism.
  Metasomatism is more complicated in the Earth's mantle, because the composition of peridotite at high temperatures can be changed by infiltration of carbonate and silicate melts and by carbon dioxide-rich and water-rich fluids, as discussed by Luth (2003). Metasomatism is thought to be particularly important in changing the composition of mantle peridotite below island arcs as water is driven out of ocean lithosphere during subduction. Metasomatism has also been considered critical for enriching source regions of some silica-undersaturated magmas. Carbonatite melts are often considered to have been responsible for enrichment of mantle peridotite in incompatible elements.
caption: Metasomatic albite + hornblende + tourmaline alteration of metamorphosed granite, Stone Mountain, Atlanta
exif: {"Image ImageDescription": "", "Image Make": "RICOH", "Image Model": "Caplio R40", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2006:07:13 12:08:09", "Image YCbCrPositioning": "Co-sited", "Image Copyright": "(C) by Caplio R40 User", "Image ExifOffset": "312", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 51, 48, 48, 0, 0, 0, 14, 0, 1, 0, 20, ... ]", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "19993", "Thumbnail JPEGInterchangeFormatLength": "5196", "EXIF ExposureTime": "1/2000", "EXIF FNumber": "5", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "400", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2006:07:13 12:08:09", "EXIF DateTimeDigitized": "2006:07:13 12:08:09", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "14/5", "EXIF ApertureValue": "23/5", "EXIF BrightnessValue": "37/5", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "33/10", "EXIF MeteringMode": "CenterWeightedAverage", "EXIF LightSource": "Cloudy weather", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "23/5", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "1600", "EXIF ExifImageLength": "1200", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "19616", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Manual", "EXIF SceneCaptureType": "Standard", "EXIF Sharpness": "Normal"}