Metasomatism


Also found in: Dictionary, Wikipedia.

metasomatism

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

Metasomatism

 

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.

REFERENCE

Korzhinskii, D. S. Teoriia metasomaticheskoi zonal’nosti Moscow, 1969.
References in periodicals archive ?
The potassic alteration metasomatism of mafic/ultramafic rocks can be indicated by F values ranging between 3 and 7 (green and orange anomalies imbedded in blue zone) as shown in figure 7d.
Part of the metaquartzite exhibited calcium metasomatism. The components of the kernstone exhibited vastly different mechanical properties under an external load; complex interactions occurred simultaneously among the components.
Barker (1965) interpreted the different alkalic rock types in the Litchfield pluton to have been produced by differentiation of an initial nepheline syenite magma; furthermore, he suggested that, in places, country rock assimilation and metasomatism resulted in the late-stage textural and mineralogical variety observed within individual phases.
Adakite-like lavas from Antisana volcano (Ecuador): evidence for slab melt metasomatism beneath the Andean northern volcanic zone.
According to Wikipedia, "Synonyms to the word metasomatism are metasomatose and metasomatic process.
Evolution of diamond resorption in a silicic aqueous fluid at 1-3GPA: Application to kimberlite emplacement and mantle metasomatism. Z.
Available isotopic data from the literature also suggest that mantle metasomatism beneath central Spain, before the end of the Variscan orogeny, is more likely caused by continental crust components, probably associated with delamination of dense crustal blocks from the thickened Variscan collisional belt.
Metasomatism accompanied by intrusions, and/or metamorphism, may be responsible for iron oxide mineralization in the Qatruyeh area.
These solutions during migration on the ground surface and through collision with limes, dolomites, or shales create the crystalline Magnesite reserves due to replacement metasomatism. The Magnesite composed through the above process is normally in coarse and crystalline form.
Original mineral assemblages and textures in the mine area have been altered, first by regional metamorphism to lower-greenschist facies, and then by dynamic metamorphism and metasomatism. Primary bedforms in the zone have been obliterated, except for small fragments of beds that lie sub-parallel to schistosity.