Also found in: Dictionary, Wikipedia.


[‚med·ə′sō·mə‚ tiz·əm]
A variety of metamorphism in which one mineral or a mineral assemblage is replaced by another of different composition without melting.



the replacement of certain minerals by others with substantial change in the chemical composition of the rock, occurring under the influence of solutions with high reactivity; the volume and solid state of the rock is usually preserved. A distinction is made between metasomatism of the magmatic stage that accompanies the intrusion of igneous rocks (for example, in connection with granitization) and postmagmatic metasomatism of the period when the rocks are cooling. Ore formation is associated with postmagmatic metasomatism. The chemical affinity of the solutions that cause metasomatism changes as the solutions cool. The following stages are distinguished in this process: the high-temperature alkaline stage (formation of skarn rocks, alkaline metasomatism), the acid stage (development of greisen and silicification), and the low-temperature alkaline stage (the development of calcareous, listvenite, beresite, and gumbeite rocks, alkaline metasomatism).

Infiltration metasomatism results from the transport of chemical components by a stream of solutions that filter through the rocks; diffusion metasomatism is associated with the diffusion of components in a relatively immobile solution that saturates the rock. At the boundary between two media that differ sharply in chemical affinity (limestones and quartzites, granites and ultrabasic rocks, and the like) there is counterdiffusion of different components (bimetasomatism).

Characteristic of the processes of metasomatism is the development of metasomatic zonation (with distinct borders between zones) resulting from the differential mobility of the components transported by the solutions. As the intensity of metasomatism grows, an increasing number of components become mobile and the number of minerals in the products of metasomatism decreases to the point where monomineralic rocks form.


Korzhinskii, D. S. Teoriia metasomaticheskoi zonal’nosti Moscow, 1969.
References in periodicals archive ?
Dykes have sometimes maintained their original combination due to hydrothermal, metasomatism and tectonic processes and contain micro-gabbro to gabbro composition, and sometimes the diabase dykes have transformed into hydrothermal metamorphic gabbros [12].
The final section covers metasomatism at the edges of the continental plates.
The effects of hydride behavior include all processes of global tectonics, volcanism, earthquakes, quiescent metasomatism, isostatic adjustment, polar wander, and generation of crustal heat, all being forms of tectonism that originates in the transition from the hydrogen-pervaded mantle to the oxygen-dominated outer Earth.
The large amount of scatter evident in the diagram may be due in part to sodium metasomatism, although the mafic rocks are fairly fresh.
gabbro, diabase and basalt) that had undergone pervasive CO2, K and S hydrothermal metasomatism (Ash 2001).
Metasomatism in the subcontinental mantle beneath the eastern Carpathians (Romania): new evidence from trace element geochemistry.
Skuppesavon Deposit - Mineralisation is associated with stratabound fracturing and sodium metasomatism and desilication, in north trending, steep westerly dipping, part skarnified acid meta-volcanics.
The settings where magnesite-rich rocks are affected by contact metamorphism or metasomatism are, therefore, truly rare.
This second style of mineralization, associated with intense metasomatism in the paragneisses, consists of wide-spread alteration and mineralization in outcrops and intervening frost-heaved float and sub-outcrop material occupying a 5.
These data indicate that the mantle source may have suffered extensive and long-term metasomatism.
The REE mineralization is probably epigenetic and may correspond to an episode of metasomatism associated with the emplacement of the Kimber alkaline intrusions (Labbe et al.
Metasomatism may also occur long before magma genesis.