/met'euh mawr"fiz euhm/, n.1. Geol. a change in the structure or constitution of a rock due to natural agencies, as pressure and heat, esp. when the rock becomes harder and more completely crystalline.2. Archaic. metamorphosis.[1835-45; META- + -MORPHISM]
* * *Mineralogic and structural changes in solid rocks caused by physical conditions different from those under which the rocks originally formed.Changes produced by surface conditions such as compaction are usually excluded. The most important agents of metamorphism are temperature (from 300°–2,200°F, or 150°–1200°C), pressure (from 10 to several hundred kilobars, or 150,000 to several million lbs. per sq in.), and stress. Dynamic metamorphism results from mechanical deformation with little long-term temperature change. Contact metamorphism results from increases in temperature with minor differential stress, is highly localized, and may occur relatively quickly. Regional metamorphism results from the general increase, usually correlated, of temperature and pressure over a large area and a long period of time, as in mountain-building processes. See also metamorphic rock.
* * *▪ geologymineralogical and structural adjustments of solid rocks to physical and chemical conditions differing from those under which the rocks originally formed. Changes produced by surface conditions such as compaction are usually excluded. The most important agents of metamorphism include temperature, pressure, and fluids. Equally as significant are changes in chemical environment that result in two metamorphic processes: (1) mechanical dislocation where a rock is deformed, especially as a consequence of differential stress; and (2) chemical recrystallization where a mineral assemblage becomes out of equilibrium due to temperature and pressure changes and a new mineral assemblage forms.Three types of metamorphism may occur depending on the relative effect of mechanical and chemical changes. Dynamic metamorphism, or cataclasis, results mainly from mechanical deformation with little long-term temperature change. Textures produced by such adjustments range from breccias composed of angular, shattered rock fragments to very fine-grained, granulated or powdered rocks with obvious foliation and lineation. Large, pre-existing mineral grains may be deformed as a result of stress. Contact metamorphism occurs primarily as a consequence of increases in temperature when differential stress is minor. A common phenomenon is the effect produced adjacent to igneous intrusions where several metamorphic zones represented by changing mineral assemblages reflect the temperature gradient from the high-temperature intrusion to the low-temperature host rocks; these zones are concentric to the intrusion. Because the volume affected is small, the pressure is near constant. Resulting rocks have equidimensional grains because of a lack of stress and are usually fine-grained due to the short duration of metamorphism. Regional metamorphism results from the general increase, usually correlated, of temperature and pressure over a large area. Grades or intensities of metamorphism are represented by different mineral assemblages that either give relative values of temperature or absolute values when calibrated against laboratory experiments. Regional metamorphism can be subdivided into different pressure-temperature conditions based on observed sequences of mineral assemblages. It may include an extreme condition, where partial melting occurs, called anatexis.Other types of metamorphism can occur. They are retrograde metamorphism, the response of mineral assemblages to decreasing temperature and pressure; metasomatism, the metamorphism that includes the addition or subtraction of components from the original assemblage; poly-metamorphism, the effect of more than one metamorphic event; and hydrothermal metamorphism, the changes that occur in the presence of water at high temperature and pressure which affect the resulting mineralogy and rate of reaction.
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См. также в других словарях:
Metamorphism — Met a*mor phism, n. (Geol.) The state or quality of being metamorphic; the process by which the material of rock masses has been more or less recrystallized by heat, pressure, etc., as in the change of sedimentary limestone to marble. Murchison.… … The Collaborative International Dictionary of English
metamorphism — (n.) 1837, from METAMORPHIC (Cf. metamorphic) + ISM (Cf. ism) … Etymology dictionary
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metamorphism — GLOSSARY OF VOLCANIC TERMS In the stricktest sense (isochemical metamorphism), the process by which consolidated rocks undergo textural and mineralogical changes brought about by changes in temperature and/or pressure. The textural and/or… … Glossary of volcanic terms
metamorphism — metamorfizmas statusas T sritis chemija apibrėžtis Uolienų struktūros, tekstūros, cheminės ir mineralinės sudėties kitimas daugiausia dėl temperatūros ir slėgio poveikio. atitikmenys: angl. metamorphism rus. метаморфизм … Chemijos terminų aiškinamasis žodynas
metamorphism — metamorphic ► ADJECTIVE ▪ (of rock) having undergone transformation by heat, pressure, or other natural agencies. DERIVATIVES metamorphism noun … English terms dictionary
metamorphism — noun Date: 1845 a change in the constitution of rock; specifically a pronounced change effected by pressure, heat, and water that results in a more compact and more highly crystalline condition … New Collegiate Dictionary
metamorphism — noun a) The process by which rocks are changed into other forms by the application of heat and/or pressure. b) The process by which insects development through life stages as, for example, those of embryo, larva, pupa and imago. The life cycle of … Wiktionary
metamorphism — metÉ™ mÉ”rfÉªzm n. metamorphosis; change in form or structure due to natural agencies (Geology) … English contemporary dictionary