Metasomatism, metasomatism (from μετά (Greek) ... and σώμα (Greek) - the body) is a natural process of substitution of mineral complexes that occurs under the influence of endogenous solutions and proceeds with a change in the chemical composition of the rock at a constant volume, at which the dissolution of old minerals and the deposition of new ones occurs almost simultaneously, so that during the substitution process, the mineral complexes always maintain a solid state.
Content
Mechanism
Metasomatism occurs during reactions between solids ( minerals ) and solutions or fluids . It manifests itself in the earth's crust both locally (regionally, on a microscale), and in large (tens and hundreds of meters) bodies of metasomatites. It can occur both at high temperatures and pressures, and in the conditions of the earth's surface.
Types of Metasomatic Processes
Depending on the method of moving the substance in solutions, diffusion and infiltration metasomatism are distinguished. Diffusion metasomatic processes include those in which the transfer of components is carried out by diffusion in an aqueous solution. In infiltration metasomatism, the movement of matter is carried out by the course of the solution due to filtration and seepage through the rocks. Under natural conditions, only infiltration or only diffusion metasomatism is extremely rare, usually there is a predominance of one or another method of substance transfer, manifested in the scale and structure of metasomatic bodies.
Depending on the geological position, metasomatism can be divided into auto-metasomatosis , contact , okolozhilnoe and regional .
- Auto metasomatosis is associated with early post-magmatic processes and usually manifests itself in the upper parts of magmatic bodies and associated vein formations. Auto-metasomatic processes include, for example, albitization in granites and serpentinization in ultrabasic rocks.
- Contact metasomatism develops in the zone of contact of the intrusion with host sedimentary rocks, as a rule. The most prominent representatives are skarn formations that develop in the early post-magmatic stage at the contact of the intrusion with the host carbonate rock (usually the contact of granites or diorites with limestone or dolomites). Contact metasomatites also include “contact leaching” processes, greisens, and secondary quartzites.
- Okolizhny metasomatosis (it is sometimes called near-ore) is associated with the formation of vein and stockwork deposits. The sedimentary metasomatites can form in a wide temperature range, but are always associated with the acid stage of the post-magmatic process.
- Regional (areal) metasomatism can occur in various geological settings, often in conditions of great depths.
Flint, alkaline, acid, and other metasomatism are distinguished depending on the chemical composition.
See also
- Metasoma
- Metasomatic rocks
- Metasomatic deposits
Literature
- Small mountain encyclopedia . In 3 t. = Mala gіrnicha encyclopedia / (In Ukrainian). Ed. V.S. Beletsky . - Donetsk: Donbass, 2004. - ISBN 966-7804-14-3 .
- Metasomatism and metasomatic breeds. Repl. Ed .: V.A. Zharikov, V.L. Rusinov. - M.: Scientific World, 1998. ISBN 5-89176-038-X .
Links
- Metasomatism // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
- Metasomatism // "Geological Dictionary" in 2 volumes, M, 1978.
- GeoWiki article