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.
Undersaturation of quartz in the fluids results from drastic temperature changes in the range 450 350 [degree]C, and in most cases the K or Na metasomatism is controlled by the subsequent disequilibrium between fluids and host rocks (Cathelineau, 1986).
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.
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.
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.
Petrological studies show potassic metasomatism and localised hydrothermal alteration within the granitic host rocks.
2004) A Geologic Study of the Platreef at Potgietersrus Platinum Mine, with Emphasis on the Magmatic Processes, Contamination and Metasomatism.
Metasomatism in oceanic and continental lithospheric mantle.
Thus, the effects of hydride behavior at the contact between the mantle and carapace include all processes of global tectonics, volcanism, earthquakes, quiescent metasomatism, magmatism, isostatic adjustment, crustal heating, and polar wander.
A correction procedure for metasomatism in an Archean greenstone belt.
Several hypotheses have been put forward for the formation of migmatites, such as partial melting (Winkler 1961), injection of foreign magmas (Sederholm 1907), metamorphic differentiation (Ashworth & McLellan 1985), and metasomatism (Olsen 1984).
The origin of migmatites is the subject of many studies discussing different migmatite-forming processes: a) Injection of externally derived granitic melts (Sederholm 1913, Zoubek 1927), b) metasomatism (Misch 1968), c) metamorphic differentiation (Robin 1979, Ashworth and McLellan 1985), and partial melting of the host rocks (Mehnert 1968, Johannes 1988, Kriegsman 2001).